Merge remote-tracking branch 'origin/master' into text

Assets/UIWidgets/Tests/RenderEditable.cs

             public override void jumpTo(double pixels) {
             }
 
-            public override IPromise<object> animateTo(double to, TimeSpan duration, Curve curve) {
-                return Promise<object>.Resolved(null);
+            public override IPromise animateTo(double to, TimeSpan duration, Curve curve) {
+                return Promise.Resolved();
             }
 
             public override ScrollDirection userScrollDirection {

Assets/UIWidgets/foundation/change_notifier.cs

             this._listeners = null;
         }
 
-        protected void notifyListeners() {
+        protected virtual void notifyListeners() {
             D.assert(this._debugAssertNotDisposed());
             if (this._listeners != null) {
                 var localListeners = new List<VoidCallback>(this._listeners);

Assets/UIWidgets/foundation/debug.cs

 
         public static bool debugPrintGestureArenaDiagnostics = true;
 
-        public static bool debugPrintHitTestResults = true;
+        public static bool debugPrintHitTestResults = false;
-        public static bool debugPrintRecognizerCallbacksTrace = true;
+        public static bool debugPrintRecognizerCallbacksTrace = false;
-        public static bool debugPrintBeginFrameBanner = true;
+        public static bool debugPrintBeginFrameBanner = false;
-        public static bool debugPrintEndFrameBanner = true;
+        public static bool debugPrintEndFrameBanner = false;
-        public static bool debugPrintScheduleFrameStacks = true;
+        public static bool debugPrintScheduleFrameStacks = false;
     }
 
     [Serializable]

Assets/UIWidgets/foundation/diagnostics.cs

         }
     }
 
+    public abstract class _NumProperty<T> : DiagnosticsProperty<T> {
+        internal _NumProperty(string name,
+            T value,
+            string ifNull = null,
+            string unit = null,
+            bool showName = true,
+            Object defaultValue = null,
+            string tooltip = null,
+            DiagnosticLevel level = DiagnosticLevel.info
+        ) : base(
+            name,
+            value,
+            ifNull: ifNull,
+            showName: showName,
+            defaultValue: defaultValue,
+            tooltip: tooltip,
+            level: level
+        ) {
+            this.unit = unit;
+        }
+
+        internal _NumProperty(string name,
+            ComputePropertyValueCallback<T> computeValue,
+            string ifNull = null,
+            string unit = null,
+            bool showName = true,
+            object defaultValue = null,
+            string tooltip = null,
+            DiagnosticLevel level = DiagnosticLevel.info
+        ) : base(
+            name,
+            computeValue,
+            ifNull: ifNull,
+            showName: showName,
+            defaultValue: defaultValue,
+            tooltip: tooltip,
+            level: level
+        ) {
+            this.unit = unit;
+        }
+
+        public override Dictionary<string, object> toJsonMap() {
+            var json = base.toJsonMap();
+            if (this.unit != null) {
+                json["unit"] = this.unit;
+            }
+
+            json["numberToString"] = this.numberToString();
+            return json;
+        }
+
+        public readonly string unit;
+
+        protected abstract string numberToString();
+
+        protected override string valueToString(TextTreeConfiguration parentConfiguration = null) {
+            if (this.value == null) {
+                return "null";
+            }
+
+            return this.unit != null ? this.numberToString() + this.unit : this.numberToString();
+        }
+    }
+
+    public class DoubleProperty : _NumProperty<double?> {
+        public DoubleProperty(string name, double? value,
+            string ifNull = null,
+            string unit = null,
+            string tooltip = null,
+            object defaultValue = null,
+            bool showName = true,
+            DiagnosticLevel level = DiagnosticLevel.info
+        ) : base(
+            name,
+            value,
+            ifNull: ifNull,
+            unit: unit,
+            tooltip: tooltip,
+            defaultValue: defaultValue,
+            showName: showName,
+            level: level
+        ) {
+        }
+
+        private DoubleProperty(
+            string name,
+            ComputePropertyValueCallback<double?> computeValue,
+            string ifNull = null,
+            bool showName = true,
+            string unit = null,
+            string tooltip = null,
+            object defaultValue = null,
+            DiagnosticLevel level = DiagnosticLevel.info
+        ) : base(
+            name,
+            computeValue,
+            showName: showName,
+            ifNull: ifNull,
+            unit: unit,
+            tooltip: tooltip,
+            defaultValue: defaultValue,
+            level: level
+        ) {
+        }
+
+        public static DoubleProperty lazy(
+            string name,
+            ComputePropertyValueCallback<double?> computeValue,
+            string ifNull = null,
+            bool showName = true,
+            string unit = null,
+            string tooltip = null,
+            object defaultValue = null,
+            DiagnosticLevel level = DiagnosticLevel.info
+        ) {
+            return new DoubleProperty(
+                name,
+                computeValue,
+                showName: showName,
+                ifNull: ifNull,
+                unit: unit,
+                tooltip: tooltip,
+                defaultValue: defaultValue,
+                level: level
+            );
+        }
+
+        protected override string numberToString() {
+            if (this.value != null) {
+                return this.value.Value.ToString("F1");
+            }
+
+            return "null";
+        }
+    }
+
+
     public class FlagProperty : DiagnosticsProperty<bool> {
         public FlagProperty(String name,
             bool value,
             this.missingIfNull = missingIfNull;
         }
 
-        private DiagnosticsProperty(
+        internal DiagnosticsProperty(
             string name,
             ComputePropertyValueCallback<T> computeValue,
             string description = null,

Assets/UIWidgets/gestures/constants.cs

         public static readonly TimeSpan kPressTimeout = new TimeSpan(0, 0, 0, 0, 100);
         
         public static readonly TimeSpan kDoubleTapTimeout = new TimeSpan(0, 0, 0, 0, 300);
+        
+        public static readonly TimeSpan kLongPressTimeout = new TimeSpan(0, 0, 0, 0, 500);
 
         public const double kMinFlingVelocity = 50.0;
 

Assets/UIWidgets/gestures/converter.cs

                     }
                         break;
                     case PointerChange.move: {
+                        bool alreadyAdded = _pointers.ContainsKey(datum.device);
+                        if (!alreadyAdded) {
+                            break;
+                        }
+                        
+                        if (!state.down) {
+                            break;
+                        }
+                        
                         Offset offset = position - state.lastPosition;
                         state.lastPosition = position;
                         yield return new PointerMoveEvent(

Assets/UIWidgets/gestures/monodrag.cs

     }
 
     public class VerticalDragGestureRecognizer : DragGestureRecognizer {
-        public VerticalDragGestureRecognizer(GestureBinding binding, Object debugOwner = null)
+        public VerticalDragGestureRecognizer(GestureBinding binding = null, Object debugOwner = null)
             : base(binding: binding, debugOwner: debugOwner) {
         }
 
     }
 
     public class HorizontalDragGestureRecognizer : DragGestureRecognizer {
-        public HorizontalDragGestureRecognizer(GestureBinding binding, Object debugOwner = null)
+        public HorizontalDragGestureRecognizer(GestureBinding binding = null, Object debugOwner = null)
             : base(binding: binding, debugOwner: debugOwner) {
         }
 
     }
 
     public class PanGestureRecognizer : DragGestureRecognizer {
-        public PanGestureRecognizer(GestureBinding binding, Object debugOwner = null)
+        public PanGestureRecognizer(GestureBinding binding = null, Object debugOwner = null)
             : base(binding: binding, debugOwner: debugOwner) {
         }
 

Assets/UIWidgets/gestures/tap.cs

     public delegate void GestureTapCancelCallback();
 
     public class TapGestureRecognizer : PrimaryPointerGestureRecognizer {
-        public TapGestureRecognizer(GestureBinding binding, object debugOwner = null)
+        public TapGestureRecognizer(GestureBinding binding = null, object debugOwner = null)
             : base(deadline: Constants.kPressTimeout, binding: binding, debugOwner: debugOwner) {
         }
 

Assets/UIWidgets/painting/basic_types.cs

 using System;
 using System.ComponentModel;
+using UIWidgets.foundation;
+using UIWidgets.widgets;
 
 namespace UIWidgets.painting {
     public enum AxisDirection {
 
             throw new Exception("unknown axisDirection");
         }
+
+        public static AxisDirection getAxisDirectionFromAxisReverseAndDirectionality(
+            BuildContext context,
+            Axis axis,
+            bool reverse
+        ) {
+            switch (axis) {
+                case Axis.horizontal:
+                    D.assert(WidgetsD.debugCheckHasDirectionality(context));
+                    TextDirection textDirection = Directionality.of(context);
+                    AxisDirection axisDirection = textDirectionToAxisDirection(textDirection);
+                    return reverse ? flipAxisDirection(axisDirection) : axisDirection;
+                case Axis.vertical:
+                    return reverse ? AxisDirection.up : AxisDirection.down;
+            }
+
+            throw new Exception("unknown axisDirection");
+        }
-    public enum RenderComparison
-    {
+    public enum RenderComparison {
         identical,
         metadata,
         paint,

Assets/UIWidgets/physics/utils.cs

 
 namespace UIWidgets.physics {
     public class PhysicsUtils {
-        public static bool nearEqual(double a, double b, double epsilon) {
+        public static bool nearEqual(double? a, double? b, double epsilon) {
+            if (a == null || b == null) {
+                return a == b;
+            }
+
-        public static bool nearZero(double a, double epsilon) {
+        public static bool nearZero(double? a, double epsilon) {
             return nearEqual(a, 0.0, epsilon);
         }
     }

Assets/UIWidgets/rendering/object.cs

 
         public List<RenderObject> _nodesNeedingLayout = new List<RenderObject>();
 
+        public bool debugDoingLayout {
+            get { return this._debugDoingLayout; }
+        }
+
+        bool _debugDoingLayout = false;
+
         public void flushLayout() {
             while (this._nodesNeedingLayout.Count > 0) {
                 var dirtyNodes = this._nodesNeedingLayout;
     }
 
     public interface RenderObjectWithChildMixin {
-        bool debugValidateChild(RenderObject child);            
+        bool debugValidateChild(RenderObject child);
-    
+
     public interface ContainerParentDataMixin<ChildType> where ChildType : RenderObject {
         ChildType previousSibling { get; set; }
         ChildType nextSibling { get; set; }

Assets/UIWidgets/rendering/proxy_box.cs

                 if (didNeedCompositing != alwaysNeedsCompositing) {
                     markNeedsCompositingBitsUpdate();
                 }
+
                 markNeedsPaint();
             }
         }
                 context.paintChild(child, offset);
                 return;
             }
+
-        
+    }
+
+    public class RenderIgnorePointer : RenderProxyBox {
+        public RenderIgnorePointer(
+            RenderBox child = null,
+            bool ignoring = true
+        ) : base(child) {
+            this._ignoring = ignoring;
+        }
+
+        public bool ignoring {
+            get { return this._ignoring; }
+            set {
+                if (value == this._ignoring) {
+                    return;
+                }
+
+                this._ignoring = value;
+            }
+        }
+
+        bool _ignoring;
+
+        public override bool hitTest(HitTestResult result, Offset position = null) {
+            return this.ignoring ? false : base.hitTest(result, position: position);
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new DiagnosticsProperty<bool>("ignoring", this.ignoring));
+        }
     }
 }

Assets/UIWidgets/rendering/viewpoint.cs

             AxisDirection axisDirection = AxisDirection.down,
             AxisDirection crossAxisDirection = AxisDirection.right,
             ViewportOffset offset = null,
-            double cacheExtent = RenderAbstractViewportUtils.defaultCacheExtent
+            double? cacheExtent = null
-            this._cacheExtent = cacheExtent;
+            this._cacheExtent = cacheExtent ?? RenderAbstractViewportUtils.defaultCacheExtent;
         }
 
         public AxisDirection axisDirection {
             double anchor = 0.0,
             List<RenderSliver> children = null,
             RenderSliver center = null,
-            double cacheExtent = RenderAbstractViewportUtils.defaultCacheExtent
+            double? cacheExtent = null
         ) : base(axisDirection, crossAxisDirection, offset, cacheExtent) {
             this.addAll(children);
             if (center == null && this.firstChild != null) {

Assets/UIWidgets/rendering/viewport_offset.cs

         public abstract void correctBy(double correction);
         public abstract void jumpTo(double pixels);
 
-        public abstract IPromise<object> animateTo(double to, TimeSpan duration, Curve curve);
+        public abstract IPromise animateTo(double to, TimeSpan duration, Curve curve);
 
         public abstract ScrollDirection userScrollDirection { get; }
 
         public override void jumpTo(double pixels) {
         }
 
-        public override IPromise<object> animateTo(double to, TimeSpan duration, Curve curve) {
-            return Promise<object>.Resolved(null);
+        public override IPromise animateTo(double to, TimeSpan duration, Curve curve) {
+            return Promise.Resolved();
         }
 
         public override ScrollDirection userScrollDirection {

Assets/UIWidgets/scheduler/ticker.cs

                 this._debugCreationStack = new StackTrace();
                 return true;
             });
+            D.assert(binding != null);
 
             this._binding = binding;
             this._onTick = onTick;

Assets/UIWidgets/widgets/basic.cs

+using System.Collections.Generic;
 using UIWidgets.foundation;
 using UIWidgets.painting;
 using UIWidgets.rendering;
         public Offset origin;
         public Alignment alignment;
         public bool transformHitTests;
-        
+
         public override RenderObject createRenderObject(BuildContext context) {
             return new RenderTransform(
                 transform: transform,
                 this.alignment
             );
         }
-        
+
         public override void updateRenderObject(BuildContext context, RenderObject renderObject) {
             ((RenderImage) renderObject).image = this.image;
             ((RenderImage) renderObject).width = this.width;
             ((RenderImage) renderObject).repeat = this.repeat;
             ((RenderImage) renderObject).centerSlice = this.centerSlice;
             ((RenderImage) renderObject).alignment = this.alignment;
-        } 
+        }
 
         public ui.Image image;
         public double width;
         public Alignment alignment;
         public ImageRepeat repeat;
         public Rect centerSlice;
+    }
+
+    public class Listener : SingleChildRenderObjectWidget {
+        public Listener(
+            Key key = null,
+            PointerDownEventListener onPointerDown = null,
+            PointerMoveEventListener onPointerMove = null,
+            PointerUpEventListener onPointerUp = null,
+            PointerCancelEventListener onPointerCancel = null,
+            HitTestBehavior behavior = HitTestBehavior.deferToChild,
+            Widget child = null
+        ) : base(key: key, child: child) {
+            this.onPointerDown = onPointerDown;
+            this.onPointerMove = onPointerMove;
+            this.onPointerUp = onPointerUp;
+            this.onPointerCancel = onPointerCancel;
+            this.behavior = behavior;
+        }
+
+        public readonly PointerDownEventListener onPointerDown;
+
+        public readonly PointerMoveEventListener onPointerMove;
+
+        public readonly PointerUpEventListener onPointerUp;
+
+        public readonly PointerCancelEventListener onPointerCancel;
+
+        public readonly HitTestBehavior behavior;
+
+        public override RenderObject createRenderObject(BuildContext context) {
+            return new RenderPointerListener(
+                onPointerDown: this.onPointerDown,
+                onPointerMove: this.onPointerMove,
+                onPointerUp: this.onPointerUp,
+                onPointerCancel: this.onPointerCancel,
+                behavior: this.behavior
+            );
+        }
+
+        public override void updateRenderObject(BuildContext context, RenderObject renderObjectRaw) {
+            var renderObject = (RenderPointerListener) renderObjectRaw;
+            renderObject.onPointerDown = this.onPointerDown;
+            renderObject.onPointerMove = this.onPointerMove;
+            renderObject.onPointerUp = this.onPointerUp;
+            renderObject.onPointerCancel = this.onPointerCancel;
+            renderObject.behavior = this.behavior;
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            List<string> listeners = new List<string>();
+            if (this.onPointerDown != null) {
+                listeners.Add("down");
+            }
+
+            if (this.onPointerMove != null) {
+                listeners.Add("move");
+            }
+
+            if (this.onPointerUp != null) {
+                listeners.Add("up");
+            }
+
+            if (this.onPointerCancel != null) {
+                listeners.Add("cancel");
+            }
+
+            properties.add(new EnumerableProperty<string>("listeners", listeners, ifEmpty: "<none>"));
+            properties.add(new EnumProperty<HitTestBehavior>("behavior", this.behavior));
+        }
+    }
+
+
+    public class IgnorePointer : SingleChildRenderObjectWidget {
+        public IgnorePointer(
+            Key key = null,
+            bool ignoring = true,
+            Widget child = null
+        ) : base(key: key, child: child) {
+            this.ignoring = ignoring;
+        }
+
+        public readonly bool ignoring;
+
+        public override RenderObject createRenderObject(BuildContext context) {
+            return new RenderIgnorePointer(
+                ignoring: this.ignoring
+            );
+        }
+
+        public override
+            void updateRenderObject(BuildContext context, RenderObject renderObjectRaw) {
+            var renderObject = (RenderIgnorePointer) renderObjectRaw;
+            renderObject.ignoring = this.ignoring;
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new DiagnosticsProperty<bool>("ignoring", this.ignoring));
+        }
     }
 }

Assets/UIWidgets/widgets/debug.cs

             });
         }
 
+        public static bool debugCheckHasDirectionality(BuildContext context) {
+            D.assert(() => {
+                if (!(context.widget is Directionality) &&
+                    context.ancestorWidgetOfExactType(typeof(Directionality)) == null) {
+                    Element element = (Element) context;
+                    throw new UIWidgetsError(
+                        "No Directionality widget found.\n" +
+                        context.widget.GetType() + " widgets require a Directionality widget ancestor.\n" +
+                        "The specific widget that could not find a Directionality ancestor was:\n" +
+                        "  " + context.widget + "\n" +
+                        "The ownership chain for the affected widget is:\n" +
+                        "  " + element.debugGetCreatorChain(10) + "\n" +
+                        "Typically, the Directionality widget is introduced by the MaterialApp " +
+                        "or WidgetsApp widget at the top of your application widget tree. It " +
+                        "determines the ambient reading direction and is used, for example, to " +
+                        "determine how to lay out text, how to interpret \"start\" and \"end\" " +
+                        "values, and to resolve EdgeInsetsDirectional, " +
+                        "AlignmentDirectional, and other *Directional objects.");
+                }
+
+                return true;
+            });
+            return true;
+        }
+
         internal static UIWidgetsErrorDetails _debugReportException(
             string context,
             Exception exception,

Assets/UIWidgets/widgets/framework.cs

             get { return this._currentElement == null ? null : this._currentElement.widget; }
         }
 
-        public State<StatefulWidget> currentState {
+        public State currentState {
-                    if (state is State<StatefulWidget>) {
-                        return (State<StatefulWidget>) state;
+                    if (state is State) {
+                        return (State) state;
                     }
                 }
 
     }
 
-    public abstract class GlobalKey<T> : GlobalKey where T : State<StatefulWidget> {
-        public new static GlobalKey key(string debugLabel = null) {
+    public abstract class GlobalKey<T> : GlobalKey where T : State {
+        public new static GlobalKey<T> key(string debugLabel = null) {
             return new LabeledGlobalKey<T>(debugLabel);
         }
 
         }
     }
 
-    public class LabeledGlobalKey<T> : GlobalKey<T> where T : State<StatefulWidget> {
+    public class LabeledGlobalKey<T> : GlobalKey<T> where T : State {
         public LabeledGlobalKey(string _debugLabel = null) {
             this._debugLabel = _debugLabel;
         }
         }
     }
 
-    public class GlobalObjectKey<T> : GlobalKey<T>, IEquatable<GlobalObjectKey<T>> where T : State<StatefulWidget> {
+    public class GlobalObjectKey<T> : GlobalKey<T>, IEquatable<GlobalObjectKey<T>> where T : State {
         public GlobalObjectKey(object value) {
             this.value = value;
         }
         public virtual void visitChildren(ElementVisitor visitor) {
         }
 
-        public void debugVisitOnstageChildren(ElementVisitor visitor) {
+        public virtual void debugVisitOnstageChildren(ElementVisitor visitor) {
             this.visitChildren(visitor);
         }
 

Assets/UIWidgets/widgets/scroll_metrics.cs

     }
 
     public static class ScrollMetricsUtils {
+        public static ScrollMetrics copyWith(ScrollMetrics it,
+            double? minScrollExtent = null,
+            double? maxScrollExtent = null,
+            double? pixels = null,
+            double? viewportDimension = null,
+            AxisDirection? axisDirection = null
+        ) {
+            return new FixedScrollMetrics(
+                minScrollExtent: minScrollExtent ?? it.minScrollExtent,
+                maxScrollExtent: maxScrollExtent ?? it.maxScrollExtent,
+                pixels: pixels ?? it.pixels,
+                viewportDimension: viewportDimension ?? it.viewportDimension,
+                axisDirection: axisDirection ?? it.axisDirection
+            );
+        }
+
         public static Axis axis(this ScrollMetrics it) {
             return AxisUtils.axisDirectionToAxis(it.axisDirection);
         }

Assets/UIWidgets/widgets/scroll_position.cs

+using System;
+using System.Collections.Generic;
+using RSG;
+using UIWidgets.animation;
+using UIWidgets.gestures;
+using UIWidgets.painting;
+using UIWidgets.physics;
-//    public abstract class ScrollPosition : ViewportOffset, ScrollMetrics {
-//        ScrollPosition(
-//            ScrollPhysics physics = null,
-//            ScrollContext context = null,
-//            bool keepScrollOffset = true,
-//            ScrollPosition oldPosition = null,
-//            string debugLabel = null
-//        ) {
-//            D.assert(physics != null);
-//            D.assert(context != null);
-//            D.assert(context.vsync != null);
-//
-//            this.physics = physics;
-//            this.context = context;
-//            this.keepScrollOffset = keepScrollOffset;
-//            this.debugLabel = debugLabel;
-//
-//            if (oldPosition != null) {
-//                this.absorb(oldPosition);
-//            }
-//
-//            if (keepScrollOffset) {
-//                this.restoreScrollOffset();
-//            }
-//        }
-//
-//        public readonly ScrollPhysics physics;
-//        public readonly ScrollContext context;
-//        public readonly bool keepScrollOffset;
-//        public readonly string debugLabel;
-//
-//        public double minScrollExtent {
-//            get { return this._minScrollExtent; }
-//        }
-//
-//        double _minScrollExtent;
-//
-//        public double maxScrollExtent {
-//            get { return this._maxScrollExtent; }
-//        }
-//
-//        double _maxScrollExtent;
-//
-//        public override double? pixels {
-//            get { return this._pixels; }
-//        }
-//
-//        double? _pixels;
-//
-//        public double viewportDimension {
-//            get { return this._viewportDimension; }
-//        }
-//
-//        double _viewportDimension;
-//
-//        public bool haveDimensions {
-//            get { return this._haveDimensions; }
-//        }
-//
-//        bool _haveDimensions = false;
-//
-//        protected virtual void absorb(ScrollPosition other) {
-//            D.assert(other != null);
-//            D.assert(other.context == context);
-//            D.assert(_pixels == null);
-//            _minScrollExtent = other.minScrollExtent;
-//            _maxScrollExtent = other.maxScrollExtent;
-//            _pixels = other._pixels;
-//            _viewportDimension = other.viewportDimension;
-//
-//            D.assert(activity == null);
-//            D.assert(other.activity != null);
-//            _activity = other.activity;
-//            other._activity = null;
-//            if (other.runtimeType != runtimeType)
-//                activity.resetActivity();
-//            context.setIgnorePointer(activity.shouldIgnorePointer);
-//            isScrollingNotifier.value = activity.isScrolling;
-//        }
-//
-//        public double setPixels(double newPixels) {
-//            D.assert(this._pixels != null);
-//            D.assert(this.context.vsync.schedulerBinding.schedulerPhase <= SchedulerPhase.transientCallbacks);
-//            if (newPixels != this.pixels) {
-//                double overscroll = this.applyBoundaryConditions(newPixels);
-//                D.assert(() => {
-//                    double delta = newPixels - this.pixels;
-//                    if (overscroll.abs() > delta.abs()) {
-//                        throw new UIWidgetsError(
-//                            string.Format(
-//                                "{0}.applyBoundaryConditions returned invalid overscroll value.\n" +
-//                                "setPixels() was called to change the scroll offset from {1} to {2}.\n" +
-//                                "That is a delta of {3} units.\n" +
-//                                "{0}.applyBoundaryConditions reported an overscroll of {4} units."
-//                                , this.GetType(), this.pixels, newPixels, delta, overscroll));
-//                    }
-//
-//                    return true;
-//                });
-//                
-//                double oldPixels = this.pixels;
-//                this._pixels = newPixels - overscroll;
-//                if (this._pixels != oldPixels) {
-//                    this.notifyListeners();
-//                    this.didUpdateScrollPositionBy(this._pixels - oldPixels);
-//                }
-//
-//                if (overscroll != 0.0) {
-//                    this.didOverscrollBy(overscroll);
-//                    return overscroll;
-//                }
-//            }
-//
-//            return 0.0;
-//        }
-//        
-//        public void correctPixels(double value) {
-//            this._pixels = value;
-//        }
-//        
-//        public override void correctBy(double correction) {
-//            D.assert(
-//                this._pixels != null,
-//                "An initial pixels value must exist by caling correctPixels on the ScrollPosition"
-//            );
-//            
-//            this._pixels += correction;
-//            this._didChangeViewportDimensionOrReceiveCorrection = true;
-//        }
-//        
-//        protected void forcePixels(double value) {
-//            D.assert(this.pixels != null);
-//            _pixels = value;
-//            notifyListeners();
-//        }
-//        
-//        protected void saveScrollOffset() {
-//            PageStorage.of(context.storageContext)?.writeState(context.storageContext, pixels);
-//        }
-//        
-//        protected void restoreScrollOffset() {
-//            if (pixels == null) {
-//                final double value = PageStorage.of(context.storageContext)?.readState(context.storageContext);
-//                if (value != null)
-//                    correctPixels(value);
-//            }
-//        }
-//    }
+    public abstract class ScrollPosition : ViewportOffset, ScrollMetrics {
+        protected ScrollPosition(
+            ScrollPhysics physics = null,
+            ScrollContext context = null,
+            bool keepScrollOffset = true,
+            ScrollPosition oldPosition = null,
+            string debugLabel = null
+        ) {
+            D.assert(physics != null);
+            D.assert(context != null);
+            D.assert(context.vsync != null);
+
+            this.physics = physics;
+            this.context = context;
+            this.keepScrollOffset = keepScrollOffset;
+            this.debugLabel = debugLabel;
+
+            if (oldPosition != null) {
+                this.absorb(oldPosition);
+            }
+
+            if (keepScrollOffset) {
+                this.restoreScrollOffset();
+            }
+        }
+
+        public readonly ScrollPhysics physics;
+
+        public readonly ScrollContext context;
+
+        public readonly bool keepScrollOffset;
+
+        public readonly string debugLabel;
+
+        public double minScrollExtent {
+            get { return this._minScrollExtent.Value; }
+        }
+
+        double? _minScrollExtent;
+
+        public double maxScrollExtent {
+            get { return this._maxScrollExtent.Value; }
+        }
+
+        double? _maxScrollExtent;
+
+        public override double pixels {
+            get { return this._pixels.Value; }
+        }
+
+        internal double? _pixels;
+
+        public double viewportDimension {
+            get { return this._viewportDimension.Value; }
+        }
+
+        double? _viewportDimension;
+
+        public bool haveDimensions {
+            get { return this._haveDimensions; }
+        }
+
+        bool _haveDimensions = false;
+
+        public abstract AxisDirection axisDirection { get; }
+
+        protected virtual void absorb(ScrollPosition other) {
+            D.assert(other != null);
+            D.assert(other.context == this.context);
+            D.assert(this._pixels == null);
+            this._minScrollExtent = other.minScrollExtent;
+            this._maxScrollExtent = other.maxScrollExtent;
+            this._pixels = other._pixels;
+            this._viewportDimension = other.viewportDimension;
+
+            D.assert(this.activity == null);
+            D.assert(other.activity != null);
+            this._activity = other.activity;
+            other._activity = null;
+            if (other.GetType() != this.GetType()) {
+                this.activity.resetActivity();
+            }
+
+            this.context.setIgnorePointer(this.activity.shouldIgnorePointer);
+            this.isScrollingNotifier.value = this.activity.isScrolling;
+        }
+
+        public virtual double setPixels(double newPixels) {
+            D.assert(this._pixels != null);
+            D.assert(this.context.vsync.schedulerBinding.schedulerPhase <= SchedulerPhase.transientCallbacks);
+            if (newPixels != this.pixels) {
+                double overscroll = this.applyBoundaryConditions(newPixels);
+                D.assert(() => {
+                    double delta = newPixels - this.pixels;
+                    if (overscroll.abs() > delta.abs()) {
+                        throw new UIWidgetsError(
+                            string.Format(
+                                "{0}.applyBoundaryConditions returned invalid overscroll value.\n" +
+                                "setPixels() was called to change the scroll offset from {1} to {2}.\n" +
+                                "That is a delta of {3} units.\n" +
+                                "{0}.applyBoundaryConditions reported an overscroll of {4} units."
+                                , this.GetType(), this.pixels, newPixels, delta, overscroll));
+                    }
+
+                    return true;
+                });
+
+                double oldPixels = this.pixels;
+                this._pixels = newPixels - overscroll;
+                if (this._pixels != oldPixels) {
+                    this.notifyListeners();
+                    this.didUpdateScrollPositionBy(this.pixels - oldPixels);
+                }
+
+                if (overscroll != 0.0) {
+                    this.didOverscrollBy(overscroll);
+                    return overscroll;
+                }
+            }
+
+            return 0.0;
+        }
+
+        public void correctPixels(double value) {
+            this._pixels = value;
+        }
+
+        public override void correctBy(double correction) {
+            D.assert(
+                this._pixels != null,
+                "An initial pixels value must exist by caling correctPixels on the ScrollPosition"
+            );
+
+            this._pixels += correction;
+            this._didChangeViewportDimensionOrReceiveCorrection = true;
+        }
+
+        protected void forcePixels(double value) {
+            D.assert(this._pixels != null);
+            this._pixels = value;
+            this.notifyListeners();
+        }
+
+        protected void saveScrollOffset() {
+            var pageStorage = PageStorage.of(this.context.storageContext);
+            if (pageStorage != null) {
+                pageStorage.writeState(this.context.storageContext, this.pixels);
+            }
+        }
+
+        protected void restoreScrollOffset() {
+            if (this._pixels == null) {
+                var pageStorage = PageStorage.of(this.context.storageContext);
+                if (pageStorage != null) {
+                    object valueRaw = pageStorage.readState(this.context.storageContext);
+                    if (valueRaw != null) {
+                        this.correctPixels((double) valueRaw);
+                    }
+                }
+            }
+        }
+
+        protected double applyBoundaryConditions(double value) {
+            double result = this.physics.applyBoundaryConditions(this, value);
+            D.assert(() => {
+                double delta = value - this.pixels;
+                if (result.abs() > delta.abs()) {
+                    throw new UIWidgetsError(
+                        string.Format(
+                            "{0}.applyBoundaryConditions returned invalid overscroll value.\n" +
+                            "The method was called to consider a change from {1} to {2}, which is a " +
+                            "delta of {3:F1} units. However, it returned an overscroll of " +
+                            "${4:F1} units, which has a greater magnitude than the delta. " +
+                            "The applyBoundaryConditions method is only supposed to reduce the possible range " +
+                            "of movement, not increase it.\n" +
+                            "The scroll extents are {5} .. {6}, and the " +
+                            "viewport dimension is {7}.",
+                            this.physics.GetType(), this.pixels, value, delta, result,
+                            this.minScrollExtent, this.maxScrollExtent, this.viewportDimension));
+                }
+
+                return true;
+            });
+
+            return result;
+        }
+
+        bool _didChangeViewportDimensionOrReceiveCorrection = true;
+
+        public override bool applyViewportDimension(double viewportDimension) {
+            if (this._viewportDimension != viewportDimension) {
+                this._viewportDimension = viewportDimension;
+                this._didChangeViewportDimensionOrReceiveCorrection = true;
+            }
+
+            return true;
+        }
+
+        public override bool applyContentDimensions(double minScrollExtent, double maxScrollExtent) {
+            if (!PhysicsUtils.nearEqual(this._minScrollExtent, minScrollExtent, Tolerance.defaultTolerance.distance) ||
+                !PhysicsUtils.nearEqual(this._maxScrollExtent, maxScrollExtent, Tolerance.defaultTolerance.distance) ||
+                this._didChangeViewportDimensionOrReceiveCorrection) {
+                this._minScrollExtent = minScrollExtent;
+                this._maxScrollExtent = maxScrollExtent;
+                this._haveDimensions = true;
+                this.applyNewDimensions();
+                this._didChangeViewportDimensionOrReceiveCorrection = false;
+            }
+
+            return true;
+        }
+
+        protected virtual void applyNewDimensions() {
+            D.assert(this._pixels != null);
+            this.activity.applyNewDimensions();
+        }
+
+        public IPromise ensureVisible(RenderObject renderObject,
+            double alignment = 0.0,
+            TimeSpan? duration = null,
+            Curve curve = null
+        ) {
+            D.assert(renderObject.attached);
+            RenderAbstractViewport viewport = RenderAbstractViewportUtils.of(renderObject);
+            D.assert(viewport != null);
+
+            double target = viewport.getOffsetToReveal(renderObject, alignment).offset.clamp(
+                this.minScrollExtent, this.maxScrollExtent);
+
+            if (target == this.pixels) {
+                return Promise.Resolved();
+            }
+
+            duration = duration ?? TimeSpan.Zero;
+            if (duration == TimeSpan.Zero) {
+                this.jumpTo(target);
+                return Promise.Resolved();
+            }
+
+            curve = curve ?? Curves.ease;
+            return this.animateTo(target, duration: duration.Value, curve: curve);
+        }
+
+        public readonly ValueNotifier<bool> isScrollingNotifier = new ValueNotifier<bool>(false);
+
+        public override bool allowImplicitScrolling {
+            get { return this.physics.allowImplicitScrolling; }
+        }
+
+        public abstract ScrollHoldController hold(VoidCallback holdCancelCallback);
+
+        public abstract Drag drag(DragStartDetails details, VoidCallback dragCancelCallback);
+
+        protected ScrollActivity activity {
+            get { return this._activity; }
+        }
+
+        ScrollActivity _activity;
+
+        public virtual void beginActivity(ScrollActivity newActivity) {
+            if (newActivity == null) {
+                return;
+            }
+
+            bool wasScrolling, oldIgnorePointer;
+            if (this._activity != null) {
+                oldIgnorePointer = this._activity.shouldIgnorePointer;
+                wasScrolling = this._activity.isScrolling;
+                if (wasScrolling && !newActivity.isScrolling) {
+                    this.didEndScroll();
+                }
+
+                this._activity.dispose();
+            } else {
+                oldIgnorePointer = false;
+                wasScrolling = false;
+            }
+
+            this._activity = newActivity;
+            if (oldIgnorePointer != this.activity.shouldIgnorePointer) {
+                this.context.setIgnorePointer(this.activity.shouldIgnorePointer);
+            }
+
+            this.isScrollingNotifier.value = this.activity.isScrolling;
+            if (!wasScrolling && this._activity.isScrolling) {
+                this.didStartScroll();
+            }
+        }
+
+        public void didStartScroll() {
+            this.activity.dispatchScrollStartNotification(
+                ScrollMetricsUtils.copyWith(this), this.context.notificationContext);
+        }
+
+        public void didUpdateScrollPositionBy(double delta) {
+            this.activity.dispatchScrollUpdateNotification(
+                ScrollMetricsUtils.copyWith(this), this.context.notificationContext, delta);
+        }
+
+        public void didEndScroll() {
+            this.activity.dispatchScrollEndNotification(
+                ScrollMetricsUtils.copyWith(this), this.context.notificationContext);
+            if (this.keepScrollOffset) {
+                this.saveScrollOffset();
+            }
+        }
+
+        public void didOverscrollBy(double value) {
+            D.assert(this.activity.isScrolling);
+            this.activity.dispatchOverscrollNotification(
+                ScrollMetricsUtils.copyWith(this), this.context.notificationContext, value);
+        }
+
+        public void didUpdateScrollDirection(ScrollDirection direction) {
+            new UserScrollNotification(metrics:
+                ScrollMetricsUtils.copyWith(this), context: this.context.notificationContext, direction: direction
+            ).dispatch(this.context.notificationContext);
+        }
+
+        public override void dispose() {
+            D.assert(this._pixels != null);
+            if (this.activity != null) {
+                this.activity.dispose();
+                this._activity = null;
+            }
+
+            base.dispose();
+        }
+
+        protected override void debugFillDescription(List<String> description) {
+            if (this.debugLabel != null) {
+                description.Add(this.debugLabel);
+            }
+
+            base.debugFillDescription(description);
+            description.Add(string.Format("range: {0:F1}..{1:F1}", this.minScrollExtent, this.maxScrollExtent));
+            description.Add(string.Format("viewport: {0:F1}", this.viewportDimension));
+        }
+    }
 }

Assets/UIWidgets/widgets/ticker_provider.cs

 using System;
 using System.Collections.Generic;
-using System.Linq;
-using UIWidgets.rendering;
-using UIWidgets.ui;
-using UnityEngine.Assertions;
+using UIWidgets.scheduler;
-        public TickerMode(Key key, bool enabled, Widget child) : base(key, child) {
+        public TickerMode(Key key = null, bool enabled = true, Widget child = null) : base(key, child) {
             this.enabled = enabled;
         }
 
-            var widget = context.inheritFromWidgetOfExactType(typeof(TickerMode));
-            return widget is TickerMode ? (widget as TickerMode).enabled : true;
+            var widget = (TickerMode) context.inheritFromWidgetOfExactType(typeof(TickerMode));
+            return widget != null ? widget.enabled : true;
-            return this.enabled != ((TickerMode)oldWidget).enabled;
+            return this.enabled != ((TickerMode) oldWidget).enabled;
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new FlagProperty("mode", value: this.enabled, ifTrue: "enabled", ifFalse: "disabled",
+                showName: true));
+        }
+    }
+
+    public abstract class SingleTickerProviderStateMixin<T> : State<T>, TickerProvider where T : StatefulWidget {
+        public SchedulerBinding schedulerBinding { get; set; }
+
+        Ticker _ticker;
+
+        public Ticker createTicker(TickerCallback onTick) {
+            D.assert(() => {
+                if (this._ticker == null) {
+                    return true;
+                }
+
+                throw new UIWidgetsError(
+                    this.GetType() + " is a SingleTickerProviderStateMixin but multiple tickers were created.\n" +
+                    "A SingleTickerProviderStateMixin can only be used as a TickerProvider once. If a " +
+                    "State is used for multiple AnimationController objects, or if it is passed to other " +
+                    "objects and those objects might use it more than one time in total, then instead of " +
+                    "mixing in a SingleTickerProviderStateMixin, use a regular TickerProviderStateMixin."
+                );
+            });
+            this._ticker = new Ticker(this.schedulerBinding, onTick, debugLabel: "created by " + this);
+            return this._ticker;
+        }
+
+        public override void dispose() {
+            D.assert(() => {
+                if (this._ticker == null || !this._ticker.isActive) {
+                    return true;
+                }
+
+                throw new UIWidgetsError(
+                    this + " was disposed with an active Ticker.\n" +
+                    this.GetType() + " created a Ticker via its SingleTickerProviderStateMixin, but at the time " +
+                    "dispose() was called on the mixin, that Ticker was still active. The Ticker must " +
+                    "be disposed before calling super.dispose(). Tickers used by AnimationControllers " +
+                    "should be disposed by calling dispose() on the AnimationController itself. " +
+                    "Otherwise, the ticker will leak.\n" +
+                    "The offending ticker was: " + this._ticker.toString(debugIncludeStack: true)
+                );
+            });
+            base.dispose();
+        }
+
+        public override void didChangeDependencies() {
+            if (this._ticker != null) {
+                this._ticker.muted = !TickerMode.of(this.context);
+            }
+
+            base.didChangeDependencies();
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            String tickerDescription = null;
+            if (this._ticker != null) {
+                if (this._ticker.isActive && this._ticker.muted) {
+                    tickerDescription = "active but muted";
+                } else if (_ticker.isActive) {
+                    tickerDescription = "active";
+                } else if (_ticker.muted) {
+                    tickerDescription = "inactive and muted";
+                } else {
+                    tickerDescription = "inactive";
+                }
+            }
+
+            properties.add(new DiagnosticsProperty<Ticker>("ticker", this._ticker, description: tickerDescription,
+                showSeparator: false, defaultValue: Diagnostics.kNullDefaultValue));
-        
-        public override Element createElement() {
-            throw new NotImplementedException();
+    }
+
+    public abstract class TickerProviderStateMixin<T> : State<T>, TickerProvider where T : StatefulWidget {
+        public SchedulerBinding schedulerBinding { get; set; }
+
+        HashSet<Ticker> _tickers;
+
+        public Ticker createTicker(TickerCallback onTick) {
+            this._tickers = this._tickers ?? new HashSet<Ticker>();
+            var result = new _WidgetTicker<T>(this.schedulerBinding, onTick, this, debugLabel: "created by " + this);
+            this._tickers.Add(result);
+            return result;
+        }
+
+        internal void _removeTicker(_WidgetTicker<T> ticker) {
+            D.assert(this._tickers != null);
+            D.assert(this._tickers.Contains(ticker));
+            this._tickers.Remove(ticker);
+        }
+
+        public override void dispose() {
+            D.assert(() => {
+                if (this._tickers != null) {
+                    foreach (Ticker ticker in this._tickers) {
+                        if (ticker.isActive) {
+                            throw new UIWidgetsError(
+                                this + " was disposed with an active Ticker.\n" +
+                                this.GetType() +
+                                " created a Ticker via its TickerProviderStateMixin, but at the time " +
+                                "dispose() was called on the mixin, that Ticker was still active. All Tickers must " +
+                                "be disposed before calling super.dispose(). Tickers used by AnimationControllers " +
+                                "should be disposed by calling dispose() on the AnimationController itself. " +
+                                "Otherwise, the ticker will leak.\n" +
+                                "The offending ticker was: " + ticker.toString(debugIncludeStack: true)
+                            );
+                        }
+                    }
+                }
+
+                return true;
+            });
+            base.dispose();
+        }
+
+        public override void didChangeDependencies() {
+            bool muted = !TickerMode.of(this.context);
+            if (this._tickers != null) {
+                foreach (Ticker ticker in this._tickers) {
+                    ticker.muted = muted;
+                }
+            }
+
+            base.didChangeDependencies();
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new DiagnosticsProperty<HashSet<Ticker>>(
+                "tickers",
+                this._tickers,
+                description: this._tickers != null ? "tracking " + this._tickers.Count + " tickers" : null,
+                defaultValue: Diagnostics.kNullDefaultValue
+            ));
+        }
+    }
+
+    class _WidgetTicker<T> : Ticker where T : StatefulWidget {
+        internal _WidgetTicker(
+            SchedulerBinding binding,
+            TickerCallback onTick,
+            TickerProviderStateMixin<T> creator,
+            string debugLabel = null) :
+            base(binding: binding, onTick: onTick, debugLabel: debugLabel) {
+            this._creator = creator;
+        }
+
+        readonly TickerProviderStateMixin<T> _creator;
+
+        public override void dispose() {
+            this._creator._removeTicker(this);
+            base.dispose();
         }
     }
 }

Assets/UIWidgets/gestures/long_press.cs

+namespace UIWidgets.gestures {
+    public delegate void GestureLongPressCallback();
+
+    public class LongPressGestureRecognizer : PrimaryPointerGestureRecognizer {
+        public LongPressGestureRecognizer(GestureBinding binding = null, object debugOwner = null) :
+            base(binding: binding, deadline: Constants.kLongPressTimeout, debugOwner: debugOwner) {
+        }
+
+        public GestureLongPressCallback onLongPress;
+
+        protected override void didExceedDeadline() {
+            this.resolve(GestureDisposition.accepted);
+            if (this.onLongPress != null) {
+                this.invokeCallback<object>("onLongPress", () => {
+                    this.onLongPress();
+                    return null;
+                });
+            }
+        }
+
+        protected override void handlePrimaryPointer(PointerEvent evt) {
+            if (evt is PointerUpEvent) {
+                this.resolve(GestureDisposition.rejected);
+            }
+        }
+
+        public override string debugDescription {
+            get { return "long press"; }
+        }
+    }
+}

Assets/UIWidgets/gestures/long_press.cs.meta

+fileFormatVersion: 2
+guid: 3315b2f4cd844e3c81aa0f074b4914a3
+timeCreated: 1537166837

Assets/UIWidgets/widgets/gesture_detector.cs

+using System;
+using System.Collections.Generic;
+using System.Linq;
+using UIWidgets.foundation;
+using UIWidgets.gestures;
+using UIWidgets.rendering;
+
+namespace UIWidgets.widgets {
+    public abstract class GestureRecognizerFactory {
+        public abstract GestureRecognizer constructorRaw();
+
+        public abstract void initializerRaw(GestureRecognizer instance);
+
+        internal abstract bool _debugAssertTypeMatches(Type type);
+    }
+
+    public abstract class GestureRecognizerFactory<T> : GestureRecognizerFactory where T : GestureRecognizer {
+        public override GestureRecognizer constructorRaw() {
+            return this.constructor();
+        }
+
+        public override void initializerRaw(GestureRecognizer instance) {
+            this.initializer((T) instance);
+        }
+
+        public abstract T constructor();
+
+        public abstract void initializer(T instance);
+
+        internal override bool _debugAssertTypeMatches(Type type) {
+            D.assert(type == typeof(T),
+                "GestureRecognizerFactory of type " + typeof(T) + " was used where type $type was specified.");
+            return true;
+        }
+    }
+
+    public delegate T GestureRecognizerFactoryConstructor<T>() where T : GestureRecognizer;
+
+    public delegate void GestureRecognizerFactoryInitializer<T>(T instance) where T : GestureRecognizer;
+
+    public class GestureRecognizerFactoryWithHandlers<T> : GestureRecognizerFactory<T> where T : GestureRecognizer {
+        public GestureRecognizerFactoryWithHandlers(GestureRecognizerFactoryConstructor<T> constructor,
+            GestureRecognizerFactoryInitializer<T> initializer) {
+            D.assert(constructor != null);
+            D.assert(initializer != null);
+
+            this._constructor = constructor;
+            this._initializer = initializer;
+        }
+
+        readonly GestureRecognizerFactoryConstructor<T> _constructor;
+
+        readonly GestureRecognizerFactoryInitializer<T> _initializer;
+
+        public override T constructor() {
+            return this._constructor();
+        }
+
+        public override void initializer(T instance) {
+            this._initializer(instance);
+        }
+    }
+
+    public class GestureDetector : StatelessWidget {
+        public GestureDetector(
+            Key key = null,
+            Widget child = null,
+            GestureTapDownCallback onTapDown = null,
+            GestureTapUpCallback onTapUp = null,
+            GestureTapCallback onTap = null,
+            GestureTapCancelCallback onTapCancel = null,
+            GestureDoubleTapCallback onDoubleTap = null,
+            GestureLongPressCallback onLongPress = null,
+            GestureDragDownCallback onVerticalDragDown = null,
+            GestureDragStartCallback onVerticalDragStart = null,
+            GestureDragUpdateCallback onVerticalDragUpdate = null,
+            GestureDragEndCallback onVerticalDragEnd = null,
+            GestureDragCancelCallback onVerticalDragCancel = null,
+            GestureDragDownCallback onHorizontalDragDown = null,
+            GestureDragStartCallback onHorizontalDragStart = null,
+            GestureDragUpdateCallback onHorizontalDragUpdate = null,
+            GestureDragEndCallback onHorizontalDragEnd = null,
+            GestureDragCancelCallback onHorizontalDragCancel = null,
+            GestureDragDownCallback onPanDown = null,
+            GestureDragStartCallback onPanStart = null,
+            GestureDragUpdateCallback onPanUpdate = null,
+            GestureDragEndCallback onPanEnd = null,
+            GestureDragCancelCallback onPanCancel = null,
+            HitTestBehavior behavior = HitTestBehavior.deferToChild) : base(key) {
+            D.assert(() => {
+                bool haveVerticalDrag =
+                    onVerticalDragStart != null || onVerticalDragUpdate != null ||
+                    onVerticalDragEnd != null;
+                bool haveHorizontalDrag =
+                    onHorizontalDragStart != null || onHorizontalDragUpdate != null ||
+                    onHorizontalDragEnd != null;
+                bool havePan = onPanStart != null || onPanUpdate != null || onPanEnd != null;
+                if (havePan) {
+                    if (haveVerticalDrag && haveHorizontalDrag) {
+                        throw new UIWidgetsError(
+                            "Incorrect GestureDetector arguments.\n" +
+                            "Simultaneously having a vertical drag gesture recognizer, a horizontal drag gesture recognizer, and a pan gesture recognizer " +
+                            "will result in the pan gesture recognizer being ignored, since the other two will catch all drags."
+                        );
+                    }
+                }
+
+                return true;
+            });
+
+            this.child = child;
+            this.onTapDown = onTapDown;
+            this.onTapUp = onTapUp;
+            this.onTap = onTap;
+            this.onTapCancel = onTapCancel;
+            this.onDoubleTap = onDoubleTap;
+            this.onLongPress = onLongPress;
+            this.onVerticalDragDown = onVerticalDragDown;
+            this.onVerticalDragStart = onVerticalDragStart;
+            this.onVerticalDragUpdate = onVerticalDragUpdate;
+            this.onVerticalDragEnd = onVerticalDragEnd;
+            this.onVerticalDragCancel = onVerticalDragCancel;
+            this.onHorizontalDragDown = onHorizontalDragDown;
+            this.onHorizontalDragStart = onHorizontalDragStart;
+            this.onHorizontalDragUpdate = onHorizontalDragUpdate;
+            this.onHorizontalDragEnd = onHorizontalDragEnd;
+            this.onHorizontalDragCancel = onHorizontalDragCancel;
+            this.onPanDown = onPanDown;
+            this.onPanStart = onPanStart;
+            this.onPanUpdate = onPanUpdate;
+            this.onPanEnd = onPanEnd;
+            this.onPanCancel = onPanCancel;
+            this.behavior = behavior;
+        }
+
+        public readonly Widget child;
+        public readonly GestureTapDownCallback onTapDown;
+        public readonly GestureTapUpCallback onTapUp;
+        public readonly GestureTapCallback onTap;
+        public readonly GestureTapCancelCallback onTapCancel;
+        public readonly GestureDoubleTapCallback onDoubleTap;
+        public readonly GestureLongPressCallback onLongPress;
+        public readonly GestureDragDownCallback onVerticalDragDown;
+        public readonly GestureDragStartCallback onVerticalDragStart;
+        public readonly GestureDragUpdateCallback onVerticalDragUpdate;
+        public readonly GestureDragEndCallback onVerticalDragEnd;
+        public readonly GestureDragCancelCallback onVerticalDragCancel;
+        public readonly GestureDragDownCallback onHorizontalDragDown;
+        public readonly GestureDragStartCallback onHorizontalDragStart;
+        public readonly GestureDragUpdateCallback onHorizontalDragUpdate;
+        public readonly GestureDragEndCallback onHorizontalDragEnd;
+        public readonly GestureDragCancelCallback onHorizontalDragCancel;
+        public readonly GestureDragDownCallback onPanDown;
+        public readonly GestureDragStartCallback onPanStart;
+        public readonly GestureDragUpdateCallback onPanUpdate;
+        public readonly GestureDragEndCallback onPanEnd;
+        public readonly GestureDragCancelCallback onPanCancel;
+        public readonly HitTestBehavior behavior;
+
+        public override Widget build(BuildContext context) {
+            var gestures = new Dictionary<Type, GestureRecognizerFactory>();
+
+            if (this.onTapDown != null ||
+                this.onTapUp != null ||
+                this.onTap != null ||
+                this.onTapCancel != null) {
+                gestures[typeof(TapGestureRecognizer)] =
+                    new GestureRecognizerFactoryWithHandlers<TapGestureRecognizer>(
+                        () => new TapGestureRecognizer(debugOwner: this),
+                        instance => {
+                            instance.onTapDown = this.onTapDown;
+                            instance.onTapUp = this.onTapUp;
+                            instance.onTap = this.onTap;
+                            instance.onTapCancel = this.onTapCancel;
+                        }
+                    );
+            }
+
+            if (this.onDoubleTap != null) {
+                gestures[typeof(DoubleTapGestureRecognizer)] =
+                    new GestureRecognizerFactoryWithHandlers<DoubleTapGestureRecognizer>(
+                        () => new DoubleTapGestureRecognizer(debugOwner: this),
+                        instance => { instance.onDoubleTap = this.onDoubleTap; }
+                    );
+            }
+
+            if (this.onLongPress != null) {
+                gestures[typeof(LongPressGestureRecognizer)] =
+                    new GestureRecognizerFactoryWithHandlers<LongPressGestureRecognizer>(
+                        () => new LongPressGestureRecognizer(debugOwner: this),
+                        instance => { instance.onLongPress = this.onLongPress; }
+                    );
+            }
+
+            if (this.onVerticalDragDown != null ||
+                this.onVerticalDragStart != null ||
+                this.onVerticalDragUpdate != null ||
+                this.onVerticalDragEnd != null ||
+                this.onVerticalDragCancel != null) {
+                gestures[typeof(VerticalDragGestureRecognizer)] =
+                    new GestureRecognizerFactoryWithHandlers<VerticalDragGestureRecognizer>(
+                        () => new VerticalDragGestureRecognizer(debugOwner: this),
+                        instance => {
+                            instance.onDown = this.onVerticalDragDown;
+                            instance.onStart = this.onVerticalDragStart;
+                            instance.onUpdate = this.onVerticalDragUpdate;
+                            instance.onEnd = this.onVerticalDragEnd;
+                            instance.onCancel = this.onVerticalDragCancel;
+                        }
+                    );
+            }
+
+            if (this.onHorizontalDragDown != null ||
+                this.onHorizontalDragStart != null ||
+                this.onHorizontalDragUpdate != null ||
+                this.onHorizontalDragEnd != null ||
+                this.onHorizontalDragCancel != null) {
+                gestures[typeof(HorizontalDragGestureRecognizer)] =
+                    new GestureRecognizerFactoryWithHandlers<HorizontalDragGestureRecognizer>(
+                        () => new HorizontalDragGestureRecognizer(debugOwner: this),
+                        instance => {
+                            instance.onDown = this.onHorizontalDragDown;
+                            instance.onStart = this.onHorizontalDragStart;
+                            instance.onUpdate = this.onHorizontalDragUpdate;
+                            instance.onEnd = this.onHorizontalDragEnd;
+                            instance.onCancel = this.onHorizontalDragCancel;
+                        }
+                    );
+            }
+
+            if (this.onPanDown != null ||
+                this.onPanStart != null ||
+                this.onPanUpdate != null ||
+                this.onPanEnd != null ||
+                this.onPanCancel != null) {
+                gestures[typeof(PanGestureRecognizer)] =
+                    new GestureRecognizerFactoryWithHandlers<PanGestureRecognizer>(
+                        () => new PanGestureRecognizer(debugOwner: this),
+                        instance => {
+                            instance.onDown = this.onPanDown;
+                            instance.onStart = this.onPanStart;
+                            instance.onUpdate = this.onPanUpdate;
+                            instance.onEnd = this.onPanEnd;
+                            instance.onCancel = this.onPanCancel;
+                        }
+                    );
+            }
+
+            return new RawGestureDetector(
+                gestures: gestures,
+                behavior: this.behavior,
+                child: this.child
+            );
+        }
+    }
+
+    public class RawGestureDetector : StatefulWidget {
+        public RawGestureDetector(
+            Key key = null,
+            Widget child = null,
+            Dictionary<Type, GestureRecognizerFactory> gestures = null,
+            HitTestBehavior? behavior = null
+        ) : base(key: key) {
+            D.assert(gestures != null);
+            this.child = child;
+            this.gestures = gestures ?? new Dictionary<Type, GestureRecognizerFactory>();
+            this.behavior = behavior;
+        }
+
+        public readonly Widget child;
+
+        public readonly Dictionary<Type, GestureRecognizerFactory> gestures;
+
+        public readonly HitTestBehavior? behavior;
+
+        public override State createState() {
+            return new RawGestureDetectorState();
+        }
+    }
+
+    public class RawGestureDetectorState : State<RawGestureDetector> {
+        Dictionary<Type, GestureRecognizer> _recognizers = new Dictionary<Type, GestureRecognizer>();
+
+        public override void initState() {
+            base.initState();
+            this._syncAll(this.widget.gestures);
+        }
+
+        public override void didUpdateWidget(StatefulWidget oldWidget) {
+            base.didUpdateWidget(oldWidget);
+            this._syncAll(this.widget.gestures);
+        }
+
+        public void replaceGestureRecognizers(Dictionary<Type, GestureRecognizerFactory> gestures) {
+            D.assert(() => {
+                if (!this.context.findRenderObject().owner.debugDoingLayout) {
+                    throw new UIWidgetsError(
+                        "Unexpected call to replaceGestureRecognizers() method of RawGestureDetectorState.\n" +
+                        "The replaceGestureRecognizers() method can only be called during the layout phase. " +
+                        "To set the gesture recognizers at other times, trigger a new build using setState() " +
+                        "and provide the new gesture recognizers as constructor arguments to the corresponding " +
+                        "RawGestureDetector or GestureDetector object.");
+                }
+
+                return true;
+            });
+            this._syncAll(gestures);
+        }
+
+        public override void dispose() {
+            foreach (GestureRecognizer recognizer in this._recognizers.Values) {
+                recognizer.dispose();
+            }
+
+            this._recognizers = null;
+            base.dispose();
+        }
+
+        void _syncAll(Dictionary<Type, GestureRecognizerFactory> gestures) {
+            D.assert(this._recognizers != null);
+            var oldRecognizers = this._recognizers;
+            this._recognizers = new Dictionary<Type, GestureRecognizer>();
+
+            foreach (Type type in gestures.Keys) {
+                D.assert(gestures[type] != null);
+                D.assert(gestures[type]._debugAssertTypeMatches(type));
+                D.assert(!this._recognizers.ContainsKey(type));
+                this._recognizers[type] = oldRecognizers[type] ?? gestures[type].constructorRaw();
+                D.assert(this._recognizers[type].GetType() == type,
+                    "GestureRecognizerFactory of type " + type + " created a GestureRecognizer of type " +
+                    this._recognizers[type].GetType() +
+                    ". The GestureRecognizerFactory must be specialized with the type of the class that it returns from its constructor method.");
+                gestures[type].initializerRaw(this._recognizers[type]);
+            }
+
+            foreach (Type type in oldRecognizers.Keys) {
+                if (!this._recognizers.ContainsKey(type)) {
+                    oldRecognizers[type].dispose();
+                }
+            }
+        }
+
+        void _handlePointerDown(PointerDownEvent evt) {
+            D.assert(this._recognizers != null);
+            foreach (GestureRecognizer recognizer in this._recognizers.Values) {
+                recognizer.addPointer(evt);
+            }
+        }
+
+        HitTestBehavior _defaultBehavior {
+            get { return this.widget.child == null ? HitTestBehavior.translucent : HitTestBehavior.deferToChild; }
+        }
+
+
+        public override Widget build(BuildContext context) {
+            Widget result = new Listener(
+                onPointerDown: this._handlePointerDown,
+                behavior: this.widget.behavior ?? this._defaultBehavior,
+                child: this.widget.child
+            );
+            return result;
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            if (this._recognizers == null) {
+                properties.add(DiagnosticsNode.message("DISPOSED"));
+            } else {
+                List<String> gestures = this._recognizers.Values.Select(recognizer => recognizer.debugDescription)
+                    .ToList();
+                properties.add(new EnumerableProperty<string>("gestures", gestures, ifEmpty: "<none>"));
+                properties.add(new EnumerableProperty<GestureRecognizer>("recognizers", this._recognizers.Values,
+                    level: DiagnosticLevel.fine));
+            }
+
+            properties.add(new EnumProperty<HitTestBehavior?>("behavior", this.widget.behavior,
+                defaultValue: Diagnostics.kNullDefaultValue));
+        }
+    }
+}

Assets/UIWidgets/widgets/gesture_detector.cs.meta

+fileFormatVersion: 2
+guid: c9c16577359d413ab2306df2227987dd
+timeCreated: 1537165902

Assets/UIWidgets/widgets/page_storage.cs

+using System;
+using System.Collections.Generic;
+using System.Linq;
+using UIWidgets.foundation;
+
+namespace UIWidgets.widgets {
+    public interface PageStorageKey {
+    }
+
+    public class PageStorageKey<T> : ValueKey<T>, PageStorageKey {
+        public PageStorageKey(T value) : base(value) {
+        }
+    }
+
+    class _StorageEntryIdentifier : IEquatable<_StorageEntryIdentifier> {
+        internal _StorageEntryIdentifier(List<PageStorageKey> keys) {
+            D.assert(keys != null);
+            this.keys = keys;
+        }
+
+        public readonly List<PageStorageKey> keys;
+
+        public bool isNotEmpty {
+            get { return this.keys.isNotEmpty(); }
+        }
+
+        public override string ToString() {
+            return string.Format("StorageEntryIdentifier({0})",
+                string.Join(":", this.keys.Select(x => x.ToString()).ToArray()));
+        }
+
+        public bool Equals(_StorageEntryIdentifier other) {
+            if (object.ReferenceEquals(null, other)) return false;
+            if (object.ReferenceEquals(this, other)) return true;
+            return this.keys.SequenceEqual(other.keys);
+        }
+
+        public override bool Equals(object obj) {
+            if (object.ReferenceEquals(null, obj)) return false;
+            if (object.ReferenceEquals(this, obj)) return true;
+            if (obj.GetType() != this.GetType()) return false;
+            return this.Equals((_StorageEntryIdentifier) obj);
+        }
+
+        public override int GetHashCode() {
+            if (this.keys == null || this.keys.isEmpty()) {
+                return 0;
+            }
+
+            var hashCode = this.keys[0].GetHashCode();
+            for (var i = 1; i < this.keys.Count; i++) {
+                hashCode = (hashCode * 397) ^ this.keys[i].GetHashCode();
+            }
+
+            return hashCode;
+        }
+
+        public static bool operator ==(_StorageEntryIdentifier left, _StorageEntryIdentifier right) {
+            return object.Equals(left, right);
+        }
+
+        public static bool operator !=(_StorageEntryIdentifier left, _StorageEntryIdentifier right) {
+            return !object.Equals(left, right);
+        }
+    }
+
+    public class PageStorageBucket {
+        static bool _maybeAddKey(BuildContext context, List<PageStorageKey> keys) {
+            Widget widget = context.widget;
+            Key key = widget.key;
+            if (key is PageStorageKey) {
+                keys.Add((PageStorageKey) key);
+            }
+
+            return !(widget is PageStorage);
+        }
+
+        List<PageStorageKey> _allKeys(BuildContext context) {
+            List<PageStorageKey> keys = new List<PageStorageKey>();
+            if (_maybeAddKey(context, keys)) {
+                context.visitAncestorElements(element => _maybeAddKey(element, keys));
+            }
+
+            return keys;
+        }
+
+        _StorageEntryIdentifier _computeIdentifier(BuildContext context) {
+            return new _StorageEntryIdentifier(this._allKeys(context));
+        }
+
+        Dictionary<object, object> _storage;
+
+        public void writeState(BuildContext context, object data, object identifier = null) {
+            this._storage = this._storage ?? new Dictionary<object, object>();
+            if (identifier != null) {
+                this._storage[identifier] = data;
+            } else {
+                _StorageEntryIdentifier contextIdentifier = this._computeIdentifier(context);
+                if (contextIdentifier.isNotEmpty) {
+                    this._storage[contextIdentifier] = data;
+                }
+            }
+        }
+
+        public object readState(BuildContext context, object identifier = null) {
+            if (this._storage == null) {
+                return null;
+            }
+
+            if (identifier != null) {
+                return this._storage[identifier];
+            }
+
+            _StorageEntryIdentifier contextIdentifier = this._computeIdentifier(context);
+            return contextIdentifier.isNotEmpty ? this._storage[contextIdentifier] : null;
+        }
+    }
+
+
+    public class PageStorage : StatelessWidget {
+        public PageStorage(
+            Key key,
+            PageStorageBucket bucket,
+            Widget child
+        ) : base(key: key) {
+            D.assert(bucket != null);
+            this.bucket = bucket;
+            this.child = child;
+        }
+
+        public readonly Widget child;
+
+        public readonly PageStorageBucket bucket;
+
+        public static PageStorageBucket of(BuildContext context) {
+            PageStorage widget = (PageStorage) context.ancestorWidgetOfExactType(typeof(PageStorage));
+            return widget == null ? null : widget.bucket;
+        }
+
+        public override Widget build(BuildContext context) {
+            return this.child;
+        }
+    }
+}

Assets/UIWidgets/widgets/page_storage.cs.meta

+fileFormatVersion: 2
+guid: 45b0579fc707492f9c779c21360b8881
+timeCreated: 1537153497

Assets/UIWidgets/widgets/primary_scroll_controller.cs

+using UIWidgets.foundation;
+
+namespace UIWidgets.widgets {
+    public class PrimaryScrollController : InheritedWidget {
+        public PrimaryScrollController(
+            Key key = null,
+            ScrollController controller = null,
+            Widget child = null
+        ) : base(key: key, child: child) {
+            D.assert(controller != null);
+        }
+
+        private PrimaryScrollController(
+            Key key = null,
+            Widget child = null
+        ) : base(key: key, child: child) {
+        }
+
+        public static PrimaryScrollController none(
+            Key key = null,
+            Widget child = null
+        ) {
+            return new PrimaryScrollController(key, child);
+        }
+
+        public readonly ScrollController controller;
+
+        public static ScrollController of(BuildContext context) {
+            PrimaryScrollController result =
+                (PrimaryScrollController) context.inheritFromWidgetOfExactType(typeof(PrimaryScrollController));
+            return result == null ? null : result.controller;
+        }
+
+        public override bool updateShouldNotify(InheritedWidget oldWidget) {
+            return this.controller != ((PrimaryScrollController) oldWidget).controller;
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new DiagnosticsProperty<ScrollController>("controller", this.controller,
+                ifNull: "no controller", showName: false));
+        }
+    }
+}

Assets/UIWidgets/widgets/primary_scroll_controller.cs.meta

+fileFormatVersion: 2
+guid: aaa3c6886fef4a7b80059bd64b818145
+timeCreated: 1537172309

Assets/UIWidgets/widgets/scroll_configuration.cs

+using UIWidgets.foundation;
+using UIWidgets.painting;
+
+namespace UIWidgets.widgets {
+    public class ScrollBehavior {
+        public Widget buildViewportChrome(BuildContext context, Widget child, AxisDirection axisDirection) {
+            return child;
+        }
+
+        public ScrollPhysics getScrollPhysics(BuildContext context) {
+            return new BouncingScrollPhysics();
+        }
+
+        public virtual bool shouldNotify(ScrollBehavior oldDelegate) {
+            return false;
+        }
+
+        public override string ToString() {
+            return this.GetType().ToString();
+        }
+    }
+
+    public class ScrollConfiguration : InheritedWidget {
+        public ScrollConfiguration(
+            Key key = null,
+            ScrollBehavior behavior = null,
+            Widget child = null
+        ) : base(key: key, child: child) {
+            D.assert(behavior != null);
+            this.behavior = behavior;
+        }
+
+        public readonly ScrollBehavior behavior;
+
+        public static ScrollBehavior of(BuildContext context) {
+            ScrollConfiguration configuration =
+                (ScrollConfiguration) context.inheritFromWidgetOfExactType(typeof(ScrollConfiguration));
+            if (configuration != null) {
+                return configuration.behavior;
+            }
+
+            return new ScrollBehavior();
+        }
+
+        public override bool updateShouldNotify(InheritedWidget oldWidgetRaw) {
+            var oldWidget = (ScrollConfiguration) oldWidgetRaw;
+
+            D.assert(this.behavior != null);
+            return this.behavior.GetType() != oldWidget.behavior.GetType()
+                   || (this.behavior != oldWidget.behavior && this.behavior.shouldNotify(oldWidget.behavior));
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new DiagnosticsProperty<ScrollBehavior>("behavior", this.behavior));
+        }
+    }
+}

Assets/UIWidgets/widgets/scroll_configuration.cs.meta

+fileFormatVersion: 2
+guid: 64f86fe6ce0a475fa47b21a73a250752
+timeCreated: 1537163722

Assets/UIWidgets/widgets/scroll_controller.cs

+using System;
+using System.Collections.Generic;
+using System.Linq;
+using RSG;
+using UIWidgets.animation;
+using UIWidgets.foundation;
+using UIWidgets.ui;
+
+namespace UIWidgets.widgets {
+    public class ScrollController : ChangeNotifier {
+        public ScrollController(
+            double initialScrollOffset = 0.0,
+            bool keepScrollOffset = true,
+            string debugLabel = null
+        ) {
+            this._initialScrollOffset = initialScrollOffset;
+            this.keepScrollOffset = keepScrollOffset;
+            this.debugLabel = debugLabel;
+        }
+
+        public virtual double initialScrollOffset {
+            get { return this._initialScrollOffset; }
+        }
+
+        readonly double _initialScrollOffset;
+
+        public readonly bool keepScrollOffset;
+
+        public readonly string debugLabel;
+
+        public IEnumerable<ScrollPosition> positions {
+            get { return this._positions; }
+        }
+
+        readonly List<ScrollPosition> _positions = new List<ScrollPosition>();
+
+        public bool hasClients {
+            get { return this._positions.isNotEmpty(); }
+        }
+
+        public ScrollPosition position {
+            get {
+                D.assert(this._positions.isNotEmpty(), "ScrollController not attached to any scroll views.");
+                D.assert(this._positions.Count == 1, "ScrollController attached to multiple scroll views.");
+                return this._positions.Single();
+            }
+        }
+
+        public double offset {
+            get { return this.position.pixels; }
+        }
+
+
+        public IPromise animateTo(double to,
+            TimeSpan duration,
+            Curve curve
+        ) {
+            D.assert(this._positions.isNotEmpty(), "ScrollController not attached to any scroll views.");
+            List<IPromise> animations = new List<IPromise>(this._positions.Count);
+            for (int i = 0; i < this._positions.Count; i += 1) {
+                animations[i] = this._positions[i].animateTo(to, duration: duration, curve: curve);
+            }
+
+            return Promise.All(animations);
+        }
+
+        public void jumpTo(double value) {
+            D.assert(this._positions.isNotEmpty(), "ScrollController not attached to any scroll views.");
+            foreach (ScrollPosition position in new List<ScrollPosition>(this._positions)) {
+                position.jumpTo(value);
+            }
+        }
+
+        public virtual void attach(ScrollPosition position) {
+            D.assert(!this._positions.Contains(position));
+            this._positions.Add(position);
+            position.addListener(this.notifyListeners);
+        }
+
+        public virtual void detach(ScrollPosition position) {
+            D.assert(this._positions.Contains(position));
+            position.removeListener(this.notifyListeners);
+            this._positions.Remove(position);
+        }
+
+        public override void dispose() {
+            foreach (ScrollPosition position in this._positions) {
+                position.removeListener(this.notifyListeners);
+            }
+
+            base.dispose();
+        }
+
+        public ScrollPosition createScrollPosition(
+            ScrollPhysics physics,
+            ScrollContext context,
+            ScrollPosition oldPosition
+        ) {
+            return new ScrollPositionWithSingleContext(
+                physics: physics,
+                context: context,
+                initialPixels: this.initialScrollOffset,
+                keepScrollOffset: this.keepScrollOffset,
+                oldPosition: oldPosition,
+                debugLabel: this.debugLabel
+            );
+        }
+
+        public override string ToString() {
+            List<string> description = new List<string>();
+            this.debugFillDescription(description);
+            return string.Format("{0}({1})", Diagnostics.describeIdentity(this),
+                string.Join(", ", description.ToArray()));
+        }
+
+        protected virtual void debugFillDescription(List<string> description) {
+            if (this.debugLabel != null) {
+                description.Add(this.debugLabel);
+            }
+
+            if (this.initialScrollOffset != 0.0) {
+                description.Add(string.Format("initialScrollOffset: {0:F1}, ", this.initialScrollOffset));
+            }
+
+            if (this._positions.isEmpty()) {
+                description.Add("no clients");
+            } else if (this._positions.Count == 1) {
+                description.Add(string.Format("one client, offset {0:F1}", this.offset));
+            } else {
+                description.Add(this._positions.Count + " clients");
+            }
+        }
+    }
+
+    public class TrackingScrollController : ScrollController {
+        public TrackingScrollController(
+            double initialScrollOffset = 0.0,
+            bool keepScrollOffset = true,
+            String debugLabel = null
+        ) : base(initialScrollOffset: initialScrollOffset,
+            keepScrollOffset: keepScrollOffset,
+            debugLabel: debugLabel) {
+        }
+
+        readonly Dictionary<ScrollPosition, VoidCallback> _positionToListener =
+            new Dictionary<ScrollPosition, VoidCallback>();
+
+        ScrollPosition _lastUpdated;
+        double? _lastUpdatedOffset;
+
+        public ScrollPosition mostRecentlyUpdatedPosition {
+            get { return this._lastUpdated; }
+        }
+
+        public override double initialScrollOffset {
+            get { return this._lastUpdatedOffset ?? base.initialScrollOffset; }
+        }
+
+        public override void attach(ScrollPosition position) {
+            base.attach(position);
+            D.assert(!this._positionToListener.ContainsKey(position));
+            this._positionToListener[position] = () => {
+                this._lastUpdated = position;
+                this._lastUpdatedOffset = position.pixels;
+            };
+            position.addListener(this._positionToListener[position]);
+        }
+
+        public override void detach(ScrollPosition position) {
+            base.detach(position);
+            D.assert(this._positionToListener.ContainsKey(position));
+            position.removeListener(this._positionToListener[position]);
+            this._positionToListener.Remove(position);
+            if (this._lastUpdated == position) {
+                this._lastUpdated = null;
+            }
+
+            if (this._positionToListener.isEmpty()) {
+                this._lastUpdatedOffset = null;
+            }
+        }
+
+        public override void dispose() {
+            foreach (ScrollPosition position in this.positions) {
+                D.assert(this._positionToListener.ContainsKey(position));
+                position.removeListener(this._positionToListener[position]);
+            }
+
+            base.dispose();
+        }
+    }
+}

Assets/UIWidgets/widgets/scroll_controller.cs.meta

+fileFormatVersion: 2
+guid: 1ae725e691fc4453b2fe1a0e5d40c642
+timeCreated: 1537160307

Assets/UIWidgets/widgets/scroll_position_with_single_context.cs

+using System;
+using System.Collections.Generic;
+using RSG;
+using UIWidgets.animation;
+using UIWidgets.foundation;
+using UIWidgets.gestures;
+using UIWidgets.painting;
+using UIWidgets.physics;
+using UIWidgets.rendering;
+using UIWidgets.ui;
+
+namespace UIWidgets.widgets {
+    public class ScrollPositionWithSingleContext : ScrollPosition, ScrollActivityDelegate {
+        public ScrollPositionWithSingleContext(
+            ScrollPhysics physics = null,
+            ScrollContext context = null,
+            double? initialPixels = 0.0,
+            bool keepScrollOffset = true,
+            ScrollPosition oldPosition = null,
+            string debugLabel = null
+        ) : base(
+            physics: physics,
+            context: context,
+            keepScrollOffset: keepScrollOffset,
+            oldPosition: oldPosition,
+            debugLabel: debugLabel
+        ) {
+            if (this._pixels == null && initialPixels != null) {
+                this.correctPixels(initialPixels.Value);
+            }
+
+            if (this.activity == null) {
+                this.goIdle();
+            }
+
+            D.assert(this.activity != null);
+        }
+
+
+        double _heldPreviousVelocity = 0.0;
+
+        public override AxisDirection axisDirection {
+            get { return this.context.axisDirection; }
+        }
+
+        public override double setPixels(double newPixels) {
+            D.assert(this.activity.isScrolling);
+            return base.setPixels(newPixels);
+        }
+
+        protected override void absorb(ScrollPosition other) {
+            base.absorb(other);
+            if (!(other is ScrollPositionWithSingleContext)) {
+                this.goIdle();
+                return;
+            }
+
+            this.activity.updateDelegate(this);
+            ScrollPositionWithSingleContext typedOther = (ScrollPositionWithSingleContext) other;
+            this._userScrollDirection = typedOther._userScrollDirection;
+            D.assert(this._currentDrag == null);
+            if (typedOther._currentDrag != null) {
+                this._currentDrag = typedOther._currentDrag;
+                this._currentDrag.updateDelegate(this);
+                typedOther._currentDrag = null;
+            }
+        }
+
+        protected override void applyNewDimensions() {
+            base.applyNewDimensions();
+            this.context.setCanDrag(this.physics.shouldAcceptUserOffset(this));
+        }
+
+        public override void beginActivity(ScrollActivity newActivity) {
+            this._heldPreviousVelocity = 0.0;
+            if (newActivity == null) {
+                return;
+            }
+
+            D.assert(newActivity.del == this);
+            base.beginActivity(newActivity);
+            if (this._currentDrag != null) {
+                this._currentDrag.dispose();
+                this._currentDrag = null;
+            }
+
+            if (!this.activity.isScrolling) {
+                this.updateUserScrollDirection(ScrollDirection.idle);
+            }
+        }
+
+        public virtual void applyUserOffset(double delta) {
+            this.updateUserScrollDirection(delta > 0.0 ? ScrollDirection.forward : ScrollDirection.reverse);
+            this.setPixels(this.pixels - this.physics.applyPhysicsToUserOffset(this, delta));
+        }
+
+        public void goIdle() {
+            this.beginActivity(new IdleScrollActivity(this));
+        }
+
+        public void goBallistic(double velocity) {
+            D.assert(this._pixels != null);
+            Simulation simulation = this.physics.createBallisticSimulation(this, velocity);
+            if (simulation != null) {
+                this.beginActivity(new BallisticScrollActivity(this, simulation, this.context.vsync));
+            } else {
+                this.goIdle();
+            }
+        }
+
+        public override ScrollDirection userScrollDirection {
+            get { return this._userScrollDirection; }
+        }
+
+        ScrollDirection _userScrollDirection = ScrollDirection.idle;
+
+        protected void updateUserScrollDirection(ScrollDirection value) {
+            if (this.userScrollDirection == value) {
+                return;
+            }
+
+            this._userScrollDirection = value;
+            this.didUpdateScrollDirection(value);
+        }
+
+        public override IPromise animateTo(double to,
+            TimeSpan duration,
+            Curve curve
+        ) {
+            if (PhysicsUtils.nearEqual(to, this.pixels, this.physics.tolerance.distance)) {
+                this.jumpTo(to);
+                return Promise.Resolved();
+            }
+
+            DrivenScrollActivity activity = new DrivenScrollActivity(
+                this,
+                from: this.pixels,
+                to: to,
+                duration: duration,
+                curve: curve,
+                vsync: this.context.vsync
+            );
+            this.beginActivity(activity);
+            return activity.done;
+        }
+
+        public override void jumpTo(double value) {
+            this.goIdle();
+            if (this.pixels != value) {
+                double oldPixels = this.pixels;
+                this.forcePixels(value);
+                this.notifyListeners();
+                this.didStartScroll();
+                this.didUpdateScrollPositionBy(this.pixels - oldPixels);
+                this.didEndScroll();
+            }
+
+            this.goBallistic(0.0);
+        }
+
+        public override ScrollHoldController hold(VoidCallback holdCancelCallback) {
+            double previousVelocity = this.activity.velocity;
+            HoldScrollActivity holdActivity = new HoldScrollActivity(
+                del: this,
+                onHoldCanceled: holdCancelCallback
+            );
+            this.beginActivity(holdActivity);
+            this._heldPreviousVelocity = previousVelocity;
+            return holdActivity;
+        }
+
+        ScrollDragController _currentDrag;
+
+        public override Drag drag(DragStartDetails details, VoidCallback dragCancelCallback) {
+            ScrollDragController drag = new ScrollDragController(
+                del: this,
+                details: details,
+                onDragCanceled: dragCancelCallback,
+                carriedVelocity: this.physics.carriedMomentum(this._heldPreviousVelocity),
+                motionStartDistanceThreshold: this.physics.dragStartDistanceMotionThreshold
+            );
+            this.beginActivity(new DragScrollActivity(this, drag));
+            D.assert(this._currentDrag == null);
+            this._currentDrag = drag;
+            return drag;
+        }
+
+        public override void dispose() {
+            if (this._currentDrag != null) {
+                this._currentDrag.dispose();
+                this._currentDrag = null;
+            }
+
+            base.dispose();
+        }
+
+        protected override void debugFillDescription(List<String> description) {
+            base.debugFillDescription(description);
+            description.Add(this.context.GetType().ToString());
+            description.Add(this.physics.ToString());
+            description.Add(this.activity.ToString());
+            description.Add(this.userScrollDirection.ToString());
+        }
+    }
+}

Assets/UIWidgets/widgets/scroll_position_with_single_context.cs.meta

+fileFormatVersion: 2
+guid: 9379d18fbd274c9b834f6d440e39959d
+timeCreated: 1537159068

Assets/UIWidgets/widgets/scroll_view.cs

+using System.Collections.Generic;
+using UIWidgets.foundation;
+using UIWidgets.painting;
+using UIWidgets.rendering;
+
+namespace UIWidgets.widgets {
+    public abstract class ScrollView : StatelessWidget {
+        protected ScrollView(
+            Key key = null,
+            Axis scrollDirection = Axis.vertical,
+            bool reverse = false,
+            ScrollController controller = null,
+            bool? primary = null,
+            ScrollPhysics physics = null,
+            bool shrinkWrap = false,
+            double? cacheExtent = null
+        ) : base(key: key) {
+            D.assert(!(controller != null && primary == true),
+                "Primary ScrollViews obtain their ScrollController via inheritance from a PrimaryScrollController widget. " +
+                "You cannot both set primary to true and pass an explicit controller.");
+
+            primary = primary ?? controller == null && scrollDirection == Axis.vertical;
+            physics = physics ?? (primary.Value ? new AlwaysScrollableScrollPhysics() : null);
+
+            this.scrollDirection = scrollDirection;
+            this.reverse = reverse;
+            this.controller = controller;
+            this.primary = primary.Value;
+            this.physics = physics;
+            this.shrinkWrap = shrinkWrap;
+            this.cacheExtent = cacheExtent;
+        }
+
+        public readonly Axis scrollDirection;
+        public readonly bool reverse;
+        public readonly ScrollController controller;
+        public readonly bool primary;
+        public readonly ScrollPhysics physics;
+        public readonly bool shrinkWrap;
+        public readonly double? cacheExtent;
+
+        protected AxisDirection getDirection(BuildContext context) {
+            return AxisUtils.getAxisDirectionFromAxisReverseAndDirectionality(context, this.scrollDirection,
+                this.reverse);
+        }
+
+        protected abstract List<Widget> buildSlivers(BuildContext context);
+
+        protected Widget buildViewport(
+            BuildContext context,
+            ViewportOffset offset,
+            AxisDirection axisDirection,
+            List<Widget> slivers
+        ) {
+            if (this.shrinkWrap) {
+                return new ShrinkWrappingViewport(
+                    axisDirection: axisDirection,
+                    offset: offset,
+                    slivers: slivers
+                );
+            }
+
+            return new Viewport(
+                axisDirection: axisDirection,
+                offset: offset,
+                slivers: slivers,
+                cacheExtent: this.cacheExtent
+            );
+        }
+
+        public override Widget build(BuildContext context) {
+            List<Widget> slivers = this.buildSlivers(context);
+            AxisDirection axisDirection = this.getDirection(context);
+
+            ScrollController scrollController = this.primary ? PrimaryScrollController.of(context) : this.controller;
+
+            Scrollable scrollable = new Scrollable(
+                axisDirection: axisDirection,
+                controller: scrollController,
+                physics: this.physics,
+                viewportBuilder: (viewportContext, offset) =>
+                    this.buildViewport(viewportContext, offset, axisDirection, slivers)
+            );
+            return this.primary && scrollController != null
+                ? (Widget) PrimaryScrollController.none(child: scrollable)
+                : scrollable;
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new EnumProperty<Axis>("scrollDirection", this.scrollDirection));
+            properties.add(new FlagProperty("reverse", value: this.reverse, ifTrue: "reversed", showName: true));
+            properties.add(new DiagnosticsProperty<ScrollController>("controller", this.controller, showName: false,
+                defaultValue: Diagnostics.kNullDefaultValue));
+            properties.add(new FlagProperty("primary", value: this.primary, ifTrue: "using primary controller",
+                showName: true));
+            properties.add(new DiagnosticsProperty<ScrollPhysics>("physics", this.physics, showName: false,
+                defaultValue: Diagnostics.kNullDefaultValue));
+            properties.add(new FlagProperty("shrinkWrap", value: this.shrinkWrap, ifTrue: "shrink-wrapping",
+                showName: true));
+        }
+    }
+
+    public abstract class BoxScrollView : ScrollView {
+        public BoxScrollView(
+            Key key = null,
+            Axis scrollDirection = Axis.vertical,
+            bool reverse = false,
+            ScrollController controller = null,
+            bool? primary = null,
+            ScrollPhysics physics = null,
+            bool shrinkWrap = false,
+            EdgeInsets padding = null,
+            double? cacheExtent = null
+        ) : base(
+            key: key,
+            scrollDirection: scrollDirection,
+            reverse: reverse,
+            controller: controller,
+            primary: primary,
+            physics: physics,
+            shrinkWrap: shrinkWrap,
+            cacheExtent: cacheExtent
+        ) {
+            this.padding = padding;
+        }
+
+        public readonly EdgeInsets padding;
+
+        protected override List<Widget> buildSlivers(BuildContext context) {
+            Widget sliver = this.buildChildLayout(context);
+
+            EdgeInsets effectivePadding = this.padding;
+            if (this.padding == null) {
+//      final MediaQueryData mediaQuery = MediaQuery.of(context, nullOk: true);
+//      if (mediaQuery != null) {
+//        // Automatically pad sliver with padding from MediaQuery.
+//        final EdgeInsets mediaQueryHorizontalPadding =
+//            mediaQuery.padding.copyWith(top: 0.0, bottom: 0.0);
+//        final EdgeInsets mediaQueryVerticalPadding =
+//            mediaQuery.padding.copyWith(left: 0.0, right: 0.0);
+//        // Consume the main axis padding with SliverPadding.
+//        effectivePadding = scrollDirection == Axis.vertical
+//            ? mediaQueryVerticalPadding
+//            : mediaQueryHorizontalPadding;
+//        // Leave behind the cross axis padding.
+//        sliver = new MediaQuery(
+//          data: mediaQuery.copyWith(
+//            padding: scrollDirection == Axis.vertical
+//                ? mediaQueryHorizontalPadding
+//                : mediaQueryVerticalPadding,
+//          ),
+//          child: sliver,
+//        );
+//      }
+            }
+
+            if (effectivePadding != null) {
+//          sliver = new SliverPadding(padding: effectivePadding, sliver: sliver);
+            }
+
+            return new List<Widget> {sliver};
+        }
+
+        protected abstract Widget buildChildLayout(BuildContext context);
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new DiagnosticsProperty<EdgeInsets>("padding", this.padding,
+                defaultValue: Diagnostics.kNullDefaultValue));
+        }
+    }
+}

Assets/UIWidgets/widgets/scroll_view.cs.meta

+fileFormatVersion: 2
+guid: 167b885cf5254b048c2bac3acf71aafa
+timeCreated: 1537171143

Assets/UIWidgets/widgets/scrollable.cs

+using System;
+using System.Collections.Generic;
+using System.Linq;
+using RSG;
+using UIWidgets.animation;
+using UIWidgets.foundation;
+using UIWidgets.gestures;
+using UIWidgets.painting;
+using UIWidgets.rendering;
+using UIWidgets.scheduler;
+
+namespace UIWidgets.widgets {
+    public delegate Widget ViewportBuilder(BuildContext context, ViewportOffset position);
+
+    public class Scrollable : StatefulWidget {
+        public Scrollable(
+            Key key = null,
+            AxisDirection axisDirection = AxisDirection.down,
+            ScrollController controller = null,
+            ScrollPhysics physics = null,
+            ViewportBuilder viewportBuilder = null
+        ) : base(key: key) {
+            D.assert(viewportBuilder != null);
+
+            this.axisDirection = axisDirection;
+            this.controller = controller;
+            this.physics = physics;
+            this.viewportBuilder = viewportBuilder;
+        }
+
+        public readonly AxisDirection axisDirection;
+
+        public readonly ScrollController controller;
+
+        public readonly ScrollPhysics physics;
+
+        public readonly ViewportBuilder viewportBuilder;
+
+        public Axis axis {
+            get { return AxisUtils.axisDirectionToAxis(this.axisDirection); }
+        }
+
+        public override State createState() {
+            return new ScrollableState();
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new EnumProperty<AxisDirection>("axisDirection", this.axisDirection));
+            properties.add(new DiagnosticsProperty<ScrollPhysics>("physics", this.physics));
+        }
+
+        public static ScrollableState of(BuildContext context) {
+            _ScrollableScope widget = (_ScrollableScope) context.inheritFromWidgetOfExactType(typeof(_ScrollableScope));
+            return widget == null ? null : widget.scrollable;
+        }
+
+        public static IPromise ensureVisible(BuildContext context,
+            double alignment = 0.0,
+            TimeSpan? duration = null,
+            Curve curve = null
+        ) {
+            duration = duration ?? TimeSpan.Zero;
+            curve = curve ?? Curves.ease;
+            List<IPromise> futures = new List<IPromise>();
+
+            ScrollableState scrollable = Scrollable.of(context);
+            while (scrollable != null) {
+                futures.Add(scrollable.position.ensureVisible(
+                    context.findRenderObject(),
+                    alignment: alignment,
+                    duration: duration,
+                    curve: curve
+                ));
+                context = scrollable.context;
+                scrollable = Scrollable.of(context);
+            }
+
+            if (futures.isEmpty() || duration == TimeSpan.Zero) {
+                return Promise.Resolved();
+            }
+
+            if (futures.Count == 1) {
+                return futures.Single();
+            }
+
+            return Promise.All(futures);
+        }
+    }
+
+    class _ScrollableScope : InheritedWidget {
+        internal _ScrollableScope(
+            Key key = null,
+            ScrollableState scrollable = null,
+            ScrollPosition position = null,
+            Widget child = null
+        ) : base(key: key, child: child) {
+            D.assert(scrollable != null);
+            D.assert(child != null);
+            this.scrollable = scrollable;
+            this.position = position;
+        }
+
+        public readonly ScrollableState scrollable;
+        public readonly ScrollPosition position;
+
+        public override bool updateShouldNotify(InheritedWidget old) {
+            return this.position != ((_ScrollableScope) old).position;
+        }
+    }
+
+    public class ScrollableState : TickerProviderStateMixin<Scrollable>, ScrollContext {
+        public SchedulerBinding schedulerBinding { get; set; }
+
+        public ScrollPosition position {
+            get { return this._position; }
+        }
+
+        ScrollPosition _position;
+
+        public AxisDirection axisDirection {
+            get { return this.widget.axisDirection; }
+        }
+
+        ScrollBehavior _configuration;
+
+        ScrollPhysics _physics;
+
+        void _updatePosition() {
+            this._configuration = ScrollConfiguration.of(this.context);
+            this._physics = this._configuration.getScrollPhysics(this.context);
+            if (this.widget.physics != null) {
+                this._physics = this.widget.physics.applyTo(this._physics);
+            }
+
+            ScrollController controller = this.widget.controller;
+            ScrollPosition oldPosition = this.position;
+            if (oldPosition != null) {
+                if (controller != null) {
+                    controller.detach(oldPosition);
+                }
+
+                this.schedulerBinding.window.scheduleMicrotask(oldPosition.dispose);
+            }
+
+            if (controller != null) {
+                this._position = controller.createScrollPosition(this._physics, this, oldPosition);
+            }
+
+            this._position = this._position
+                             ?? new ScrollPositionWithSingleContext(physics: this._physics, context: this,
+                                 oldPosition: oldPosition);
+
+            D.assert(this.position != null);
+            if (controller != null) {
+                controller.attach(this.position);
+            }
+        }
+
+        public override void didChangeDependencies() {
+            base.didChangeDependencies();
+            this._updatePosition();
+        }
+
+        bool _shouldUpdatePosition(Scrollable oldWidget) {
+            ScrollPhysics newPhysics = this.widget.physics;
+            ScrollPhysics oldPhysics = oldWidget.physics;
+            do {
+                Type newPhysicsType = newPhysics != null ? newPhysics.GetType() : null;
+                Type oldPhysicsType = oldPhysics != null ? oldPhysics.GetType() : null;
+
+                if (newPhysicsType != oldPhysicsType) {
+                    return true;
+                }
+
+                if (newPhysics != null) {
+                    newPhysics = newPhysics.parent;
+                }
+
+                if (oldPhysics != null) {
+                    oldPhysics = oldPhysics.parent;
+                }
+            } while (newPhysics != null || oldPhysics != null);
+
+            Type controllerType = widget.controller == null ? null : widget.controller.GetType();
+            Type oldControllerType = oldWidget.controller == null ? null : oldWidget.controller.GetType();
+            return controllerType != oldControllerType;
+        }
+
+        public override void didUpdateWidget(StatefulWidget oldWidgetRaw) {
+            Scrollable oldWidget = (Scrollable) oldWidgetRaw;
+            base.didUpdateWidget(oldWidget);
+
+            if (this.widget.controller != oldWidget.controller) {
+                if (oldWidget.controller != null) {
+                    oldWidget.controller.detach(this.position);
+                }
+
+                if (this.widget.controller != null) {
+                    this.widget.controller.attach(this.position);
+                }
+            }
+
+            if (this._shouldUpdatePosition(oldWidget)) {
+                this._updatePosition();
+            }
+        }
+
+        public override void dispose() {
+            if (this.widget.controller != null) {
+                this.widget.controller.detach(this.position);
+            }
+
+            this.position.dispose();
+            base.dispose();
+        }
+
+        GlobalKey<RawGestureDetectorState> _gestureDetectorKey = GlobalKey<RawGestureDetectorState>.key();
+        GlobalKey _ignorePointerKey = GlobalKey.key();
+
+        Dictionary<Type, GestureRecognizerFactory> _gestureRecognizers =
+            new Dictionary<Type, GestureRecognizerFactory>();
+
+        bool _shouldIgnorePointer = false;
+
+        bool _lastCanDrag;
+        Axis _lastAxisDirection;
+
+        public void setCanDrag(bool canDrag) {
+            if (canDrag == this._lastCanDrag && (!canDrag || this.widget.axis == this._lastAxisDirection)) {
+                return;
+            }
+
+            if (!canDrag) {
+                this._gestureRecognizers = new Dictionary<Type, GestureRecognizerFactory>();
+            } else {
+                switch (this.widget.axis) {
+                    case Axis.vertical:
+                        this._gestureRecognizers = new Dictionary<Type, GestureRecognizerFactory>();
+                        this._gestureRecognizers.Add(typeof(VerticalDragGestureRecognizer),
+                            new GestureRecognizerFactoryWithHandlers<VerticalDragGestureRecognizer>(
+                                () => new VerticalDragGestureRecognizer(),
+                                instance => {
+                                    instance.onDown = this._handleDragDown;
+                                    instance.onStart = this._handleDragStart;
+                                    instance.onUpdate = this._handleDragUpdate;
+                                    instance.onEnd = this._handleDragEnd;
+                                    instance.onCancel = this._handleDragCancel;
+                                    instance.minFlingDistance =
+                                        this._physics == null ? (double?) null : this._physics.minFlingDistance;
+                                    instance.minFlingVelocity =
+                                        this._physics == null ? (double?) null : this._physics.minFlingVelocity;
+                                    instance.maxFlingVelocity =
+                                        this._physics == null ? (double?) null : this._physics.maxFlingVelocity;
+                                }
+                            ));
+                        break;
+                    case Axis.horizontal:
+                        this._gestureRecognizers = new Dictionary<Type, GestureRecognizerFactory>();
+                        this._gestureRecognizers.Add(typeof(HorizontalDragGestureRecognizer),
+                            new GestureRecognizerFactoryWithHandlers<HorizontalDragGestureRecognizer>(
+                                () => new HorizontalDragGestureRecognizer(),
+                                instance => {
+                                    instance.onDown = this._handleDragDown;
+                                    instance.onStart = this._handleDragStart;
+                                    instance.onUpdate = this._handleDragUpdate;
+                                    instance.onEnd = this._handleDragEnd;
+                                    instance.onCancel = this._handleDragCancel;
+                                    instance.minFlingDistance =
+                                        this._physics == null ? (double?) null : this._physics.minFlingDistance;
+                                    instance.minFlingVelocity =
+                                        this._physics == null ? (double?) null : this._physics.minFlingVelocity;
+                                    instance.maxFlingVelocity =
+                                        this._physics == null ? (double?) null : this._physics.maxFlingVelocity;
+                                }
+                            ));
+                        break;
+                }
+            }
+
+            this._lastCanDrag = canDrag;
+            this._lastAxisDirection = this.widget.axis;
+            if (this._gestureDetectorKey.currentState != null) {
+                this._gestureDetectorKey.currentState.replaceGestureRecognizers(this._gestureRecognizers);
+            }
+        }
+
+        public TickerProvider vsync {
+            get { return this; }
+        }
+
+        public void setIgnorePointer(bool value) {
+            if (this._shouldIgnorePointer == value) {
+                return;
+            }
+
+            this._shouldIgnorePointer = value;
+            if (this._ignorePointerKey.currentContext != null) {
+                var renderBox = (RenderIgnorePointer) this._ignorePointerKey.currentContext.findRenderObject();
+                renderBox.ignoring = this._shouldIgnorePointer;
+            }
+        }
+
+        public BuildContext notificationContext {
+            get { return this._gestureDetectorKey.currentContext; }
+        }
+
+        public BuildContext storageContext {
+            get { return this.context; }
+        }
+
+        Drag _drag;
+
+        ScrollHoldController _hold;
+
+        void _handleDragDown(DragDownDetails details) {
+            D.assert(this._drag == null);
+            D.assert(this._hold == null);
+            this._hold = this.position.hold(this._disposeHold);
+        }
+
+        void _handleDragStart(DragStartDetails details) {
+            D.assert(this._drag == null);
+            this._drag = this.position.drag(details, this._disposeDrag);
+            D.assert(this._drag != null);
+            D.assert(this._hold == null);
+        }
+
+        void _handleDragUpdate(DragUpdateDetails details) {
+            D.assert(this._hold == null || this._drag == null);
+            if (this._drag != null) {
+                this._drag.update(details);
+            }
+        }
+
+        void _handleDragEnd(DragEndDetails details) {
+            D.assert(this._hold == null || this._drag == null);
+            if (this._drag != null) {
+                this._drag.end(details);
+            }
+
+            D.assert(this._drag == null);
+        }
+
+        void _handleDragCancel() {
+            D.assert(this._hold == null || this._drag == null);
+            if (this._hold != null) {
+                this._hold.cancel();
+            }
+
+            if (this._drag != null) {
+                this._drag.cancel();
+            }
+
+            D.assert(this._hold == null);
+            D.assert(this._drag == null);
+        }
+
+        void _disposeHold() {
+            this._hold = null;
+        }
+
+        void _disposeDrag() {
+            this._drag = null;
+        }
+
+        public override Widget build(BuildContext context) {
+            D.assert(this.position != null);
+
+            Widget result = new RawGestureDetector(
+                key: this._gestureDetectorKey,
+                gestures: this._gestureRecognizers,
+                behavior: HitTestBehavior.opaque,
+                child: new IgnorePointer(
+                    key: this._ignorePointerKey,
+                    ignoring: this._shouldIgnorePointer,
+                    child: new _ScrollableScope(
+                        scrollable: this,
+                        position: this.position,
+                        child: this.widget.viewportBuilder(context, this.position)
+                    )
+                )
+            );
+
+            return this._configuration.buildViewportChrome(context, result, this.widget.axisDirection);
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new DiagnosticsProperty<ScrollPosition>("position", this.position));
+        }
+    }
+}

Assets/UIWidgets/widgets/scrollable.cs.meta

+fileFormatVersion: 2
+guid: c3917312a54a4263a839cd628ae99010
+timeCreated: 1537160124

Assets/UIWidgets/widgets/viewport.cs

+using System;
+using System.Collections.Generic;
+using System.Linq;
+using UIWidgets.foundation;
+using UIWidgets.painting;
+using UIWidgets.rendering;
+
+namespace UIWidgets.widgets {
+    public class Viewport : MultiChildRenderObjectWidget {
+        public Viewport(
+            Key key = null,
+            AxisDirection axisDirection = AxisDirection.down,
+            AxisDirection? crossAxisDirection = null,
+            double anchor = 0.0,
+            ViewportOffset offset = null,
+            Key center = null,
+            double? cacheExtent = null,
+            List<Widget> slivers = null
+        ) : base(key: key, children: slivers) {
+            D.assert(offset != null);
+            slivers = slivers ?? new List<Widget>();
+            D.assert(slivers != null);
+            D.assert(center == null || slivers.Count(child => child.key == center) == 1);
+
+            this.axisDirection = axisDirection;
+            this.crossAxisDirection = crossAxisDirection;
+            this.anchor = anchor;
+            this.offset = offset;
+            this.center = center;
+            this.cacheExtent = cacheExtent;
+        }
+
+        public readonly AxisDirection axisDirection;
+
+        public readonly AxisDirection? crossAxisDirection;
+
+        public readonly double anchor;
+
+        public readonly ViewportOffset offset;
+
+        public readonly Key center;
+
+        public readonly double? cacheExtent;
+
+        public static AxisDirection getDefaultCrossAxisDirection(BuildContext context, AxisDirection axisDirection) {
+            switch (axisDirection) {
+                case AxisDirection.up:
+                    return AxisUtils.textDirectionToAxisDirection(Directionality.of(context));
+                case AxisDirection.right:
+                    return AxisDirection.down;
+                case AxisDirection.down:
+                    return AxisUtils.textDirectionToAxisDirection(Directionality.of(context));
+                case AxisDirection.left:
+                    return AxisDirection.down;
+            }
+
+
+            throw new Exception("unknown axisDirection");
+        }
+
+
+        public override RenderObject createRenderObject(BuildContext context) {
+            return new RenderViewport(
+                axisDirection: this.axisDirection,
+                crossAxisDirection: this.crossAxisDirection ??
+                                    Viewport.getDefaultCrossAxisDirection(context, this.axisDirection),
+                anchor: this.anchor,
+                offset: this.offset,
+                cacheExtent: this.cacheExtent
+            );
+        }
+
+        public override void updateRenderObject(BuildContext context, RenderObject renderObjectRaw) {
+            var renderObject = (RenderViewport) renderObjectRaw;
+            renderObject.axisDirection = this.axisDirection;
+            renderObject.crossAxisDirection = this.crossAxisDirection ??
+                                              Viewport.getDefaultCrossAxisDirection(context, this.axisDirection);
+            renderObject.anchor = this.anchor;
+            renderObject.offset = this.offset;
+            renderObject.cacheExtent = this.cacheExtent ?? RenderAbstractViewportUtils.defaultCacheExtent;
+        }
+
+        public override Element createElement() {
+            return new _ViewportElement(this);
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new EnumProperty<AxisDirection>("axisDirection", this.axisDirection));
+            properties.add(new EnumProperty<AxisDirection?>("crossAxisDirection", this.crossAxisDirection,
+                defaultValue: Diagnostics.kNullDefaultValue));
+            properties.add(new DoubleProperty("anchor", this.anchor));
+            properties.add(new DiagnosticsProperty<ViewportOffset>("offset", this.offset));
+            if (this.center != null) {
+                properties.add(new DiagnosticsProperty<Key>("center", this.center));
+            } else if (this.children.isNotEmpty() && this.children.First().key != null) {
+                properties.add(new DiagnosticsProperty<Key>("center", this.children.First().key, tooltip: "implicit"));
+            }
+        }
+    }
+
+
+    class _ViewportElement : MultiChildRenderObjectElement {
+        internal _ViewportElement(Viewport widget) : base(widget) {
+        }
+
+        public new Viewport widget {
+            get { return (Viewport) base.widget; }
+        }
+
+        public new RenderViewport renderObject {
+            get { return (RenderViewport) base.renderObject; }
+        }
+
+        public override void mount(Element parent, object newSlot) {
+            base.mount(parent, newSlot);
+            this._updateCenter();
+        }
+
+        public override void update(Widget newWidget) {
+            base.update(newWidget);
+            this._updateCenter();
+        }
+
+        void _updateCenter() {
+            if (this.widget.center != null) {
+                this.renderObject.center = (RenderSliver) this.children.Single(
+                    element => element.widget.key == this.widget.center).renderObject;
+            } else if (this.children.Any()) {
+                this.renderObject.center = (RenderSliver) this.children.First().renderObject;
+            } else {
+                this.renderObject.center = null;
+            }
+        }
+
+        public override void debugVisitOnstageChildren(ElementVisitor visitor) {
+            this.children.Where(e => {
+                RenderSliver renderSliver = (RenderSliver) e.renderObject;
+                return renderSliver.geometry.visible;
+            }).ToList().ForEach(e => visitor(e));
+        }
+    }
+
+
+    public class ShrinkWrappingViewport : MultiChildRenderObjectWidget {
+        public ShrinkWrappingViewport(
+            Key key = null,
+            AxisDirection axisDirection = AxisDirection.down,
+            AxisDirection? crossAxisDirection = null,
+            ViewportOffset offset = null,
+            List<Widget> slivers = null
+        ) : base(key: key, children: slivers) {
+            D.assert(offset != null);
+
+            this.axisDirection = axisDirection;
+            this.crossAxisDirection = crossAxisDirection;
+            this.offset = offset;
+        }
+
+        public readonly AxisDirection axisDirection;
+
+        public readonly AxisDirection? crossAxisDirection;
+
+        public readonly ViewportOffset offset;
+
+        public override RenderObject createRenderObject(BuildContext context) {
+            return new RenderShrinkWrappingViewport(
+                axisDirection: this.axisDirection,
+                crossAxisDirection:
+                this.crossAxisDirection ?? Viewport.getDefaultCrossAxisDirection(context, this.axisDirection),
+                offset: this.offset
+            );
+        }
+
+        public override void updateRenderObject(BuildContext context, RenderObject renderObjectRaw) {
+            var renderObject = (RenderShrinkWrappingViewport) renderObjectRaw;
+            renderObject.axisDirection = this.axisDirection;
+
+            renderObject.crossAxisDirection =
+                this.crossAxisDirection ?? Viewport.getDefaultCrossAxisDirection(context, this.axisDirection);
+            renderObject.offset = this.offset;
+        }
+
+        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+            base.debugFillProperties(properties);
+            properties.add(new EnumProperty<AxisDirection>("axisDirection", this.axisDirection));
+            properties.add(new EnumProperty<AxisDirection?>("crossAxisDirection", this.crossAxisDirection,
+                defaultValue: Diagnostics.kNullDefaultValue));
+            properties.add(new DiagnosticsProperty<ViewportOffset>("offset", this.offset));
+        }
+    }
+}

Assets/UIWidgets/widgets/viewport.cs.meta

+fileFormatVersion: 2
+guid: cbc0da359825401197d0c5772ebdaac1
+timeCreated: 1537172721