com.unity.uiwidgets/com.unity.uiwidgets/Runtime/widgets/scroll_view.cs

using System.Collections.Generic;
using com.unity.uiwidgets.Runtime.rendering;
using Unity.UIWidgets.foundation;
using Unity.UIWidgets.gestures;
using Unity.UIWidgets.painting;
using Unity.UIWidgets.rendering;
using UnityEngine;

namespace Unity.UIWidgets.widgets {
    public enum ScrollViewKeyboardDismissBehavior {
        manual,
        onDrag
    }
    
    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,
            Key center = null,
            float anchor = 0.0f,
            float? cacheExtent = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start,
            ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual
        ) : 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.");
            D.assert(!shrinkWrap || center == null);
            D.assert(anchor >= 0.0f && anchor <= 1.0f);

            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.center = center;
            this.anchor = anchor;
            this.cacheExtent = cacheExtent;
            this.dragStartBehavior = dragStartBehavior;
            this.keyboardDismissBehavior = keyboardDismissBehavior;
        }

        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 Key center;
        public readonly float anchor;
        public readonly float? cacheExtent;
        public readonly DragStartBehavior dragStartBehavior;
        public readonly ScrollViewKeyboardDismissBehavior keyboardDismissBehavior;

        protected AxisDirection getDirection(BuildContext context) {
            return LayoutUtils.getAxisDirectionFromAxisReverseAndDirectionality(
                context, scrollDirection, reverse);
        }

        protected abstract List<Widget> buildSlivers(BuildContext context);

        protected virtual Widget buildViewport(
            BuildContext context,
            ViewportOffset offset,
            AxisDirection axisDirection,
            List<Widget> slivers
        ) {
            if (shrinkWrap) {
                return new ShrinkWrappingViewport(
                    axisDirection: axisDirection,
                    offset: offset,
                    slivers: slivers
                );
            }

            return new Viewport(
                axisDirection: axisDirection,
                offset: offset,
                slivers: slivers,
                cacheExtent: cacheExtent,
                center: center,
                anchor: anchor
            );
        }

        public override Widget build(BuildContext context) {
            List<Widget> slivers = buildSlivers(context);
            AxisDirection axisDirection = getDirection(context);

            ScrollController scrollController = primary ? PrimaryScrollController.of(context) : controller;

            Scrollable scrollable = new Scrollable(
                dragStartBehavior: dragStartBehavior,
                axisDirection: axisDirection,
                controller: scrollController,
                physics: physics,
                viewportBuilder: (viewportContext, offset) =>
                    buildViewport(viewportContext, offset, axisDirection, slivers)
            );
            
            Widget scrollableResult = primary && scrollController != null
                ? (Widget) PrimaryScrollController.none(child: scrollable)
                : scrollable;

            if (keyboardDismissBehavior == ScrollViewKeyboardDismissBehavior.onDrag) {
                return new NotificationListener<ScrollUpdateNotification>(
                    child: scrollableResult,
                    onNotification: (ScrollUpdateNotification notification) => {
                        FocusScopeNode focusScope = FocusScope.of(context);
                        if (notification.dragDetails != null && focusScope.hasFocus) {
                            focusScope.unfocus();
                        }

                        return false;
                    }
                );
            }
            else {
                return scrollableResult;
            }
        }

        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
            base.debugFillProperties(properties);
            properties.add(new EnumProperty<Axis>("scrollDirection", scrollDirection));
            properties.add(new FlagProperty("reverse", value: reverse, ifTrue: "reversed", showName: true));
            properties.add(new DiagnosticsProperty<ScrollController>("controller", controller, showName: false,
                defaultValue: foundation_.kNullDefaultValue));
            properties.add(new FlagProperty("primary", value: primary, ifTrue: "using primary controller",
                showName: true));
            properties.add(new DiagnosticsProperty<ScrollPhysics>("physics", physics, showName: false,
                defaultValue: foundation_.kNullDefaultValue));
            properties.add(new FlagProperty("shrinkWrap", value: shrinkWrap, ifTrue: "shrink-wrapping",
                showName: true));
        }
    }

    public class CustomScrollView : ScrollView {
        public CustomScrollView(
            Key key = null,
            Axis scrollDirection = Axis.vertical,
            bool reverse = false,
            ScrollController controller = null,
            bool? primary = null,
            ScrollPhysics physics = null,
            bool shrinkWrap = false,
            Key center = null,
            float anchor = 0.0f,
            float? cacheExtent = null,
            List<Widget> slivers = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start
        ) : base(
            key: key,
            scrollDirection: scrollDirection,
            reverse: reverse,
            controller: controller,
            primary: primary,
            physics: physics,
            shrinkWrap: shrinkWrap,
            center: center,
            anchor: anchor,
            cacheExtent: cacheExtent,
            dragStartBehavior: dragStartBehavior
        ) {
            this.slivers = slivers ?? new List<Widget>();
        }

        public readonly List<Widget> slivers;

        protected override List<Widget> buildSlivers(BuildContext context) {
            return slivers;
        }
    }

    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,
            float? cacheExtent = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start,
            ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual
        ) : base(
            key: key,
            scrollDirection: scrollDirection,
            reverse: reverse,
            controller: controller,
            primary: primary,
            physics: physics,
            shrinkWrap: shrinkWrap,
            cacheExtent: cacheExtent,
            dragStartBehavior: dragStartBehavior,
            keyboardDismissBehavior: keyboardDismissBehavior
        ) {
            this.padding = padding;
        }

        public readonly EdgeInsets padding;

        protected override List<Widget> buildSlivers(BuildContext context) {
            Widget sliver = buildChildLayout(context);

            EdgeInsets effectivePadding = padding; // no need to check MediaQuery for now.
            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", padding,
                defaultValue: foundation_.kNullDefaultValue));
        }
    }

    public class ListView : BoxScrollView {
        public ListView(
            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,
            float? itemExtent = null,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            float? cacheExtent = null,
            List<Widget> children = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start,
            ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual
        ) : base(
            key: key,
            scrollDirection: scrollDirection,
            reverse: reverse,
            controller: controller,
            primary: primary,
            physics: physics,
            shrinkWrap: shrinkWrap,
            padding: padding,
            cacheExtent: cacheExtent,
            dragStartBehavior: dragStartBehavior,
            keyboardDismissBehavior: keyboardDismissBehavior
        ) {
            this.itemExtent = itemExtent;
            childrenDelegate = new SliverChildListDelegate(
                children,
                addAutomaticKeepAlives: addAutomaticKeepAlives,
                addRepaintBoundaries: addRepaintBoundaries
            );
        }

        ListView(
            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,
            float? itemExtent = null,
            IndexedWidgetBuilder itemBuilder = null,
            int? itemCount = null,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            float? cacheExtent = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start,
            ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual
        ) : base(key: key,
            scrollDirection: scrollDirection,
            reverse: reverse,
            controller: controller,
            primary: primary,
            physics: physics,
            shrinkWrap: shrinkWrap,
            padding: padding,
            cacheExtent: cacheExtent,
            dragStartBehavior: dragStartBehavior,
            keyboardDismissBehavior: keyboardDismissBehavior
        ) {
            D.assert(itemCount == null || itemCount >= 0);
            this.itemExtent = itemExtent;
            childrenDelegate = new SliverChildBuilderDelegate(
                itemBuilder,
                childCount: itemCount,
                addAutomaticKeepAlives: addAutomaticKeepAlives,
                addRepaintBoundaries: addRepaintBoundaries
            );
        }

        public static ListView builder(
            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,
            float? itemExtent = null,
            IndexedWidgetBuilder itemBuilder = null,
            int? itemCount = null,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            float? cacheExtent = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start,
            ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual
        ) {
            return new ListView(
                key: key,
                scrollDirection: scrollDirection,
                reverse: reverse,
                controller: controller,
                primary: primary,
                physics: physics,
                shrinkWrap: shrinkWrap,
                padding: padding,
                cacheExtent: cacheExtent,
                itemExtent: itemExtent,
                itemBuilder: itemBuilder,
                itemCount: itemCount,
                addAutomaticKeepAlives: addAutomaticKeepAlives,
                addRepaintBoundaries: addRepaintBoundaries,
                dragStartBehavior: dragStartBehavior,
                keyboardDismissBehavior: keyboardDismissBehavior
            );
        }


        ListView(
            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,
            IndexedWidgetBuilder itemBuilder = null,
            IndexedWidgetBuilder separatorBuilder = null,
            int itemCount = 0,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            float? cacheExtent = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start,
            ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual
        ) : base(
            key: key,
            scrollDirection: scrollDirection,
            reverse: reverse,
            controller: controller,
            primary: primary,
            physics: physics,
            shrinkWrap: shrinkWrap,
            padding: padding,
            cacheExtent: cacheExtent,
            dragStartBehavior: dragStartBehavior,
            keyboardDismissBehavior: keyboardDismissBehavior
        ) {
            D.assert(itemBuilder != null);
            D.assert(separatorBuilder != null);
            D.assert(itemCount >= 0);
            itemExtent = null;
            childrenDelegate = new SliverChildBuilderDelegate(
                (context, index) => {
                    int itemIndex = index / 2;
                    Widget widget = null;
                    if (index % 2 == 0) {
                        widget = itemBuilder(context, itemIndex);
                    }
                    else {
                        widget = separatorBuilder(context, itemIndex);
                        D.assert(() => {
                            if (widget == null) {
                                throw new UIWidgetsError("separatorBuilder cannot return null.");
                            }

                            return true;
                        });
                    }
                    return widget;
                },
                childCount: _computeActualChildCount(itemCount),
                addAutomaticKeepAlives: addAutomaticKeepAlives,
                addRepaintBoundaries: addRepaintBoundaries
            );
        }

        public static ListView seperated(
            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,
            IndexedWidgetBuilder itemBuilder = null,
            IndexedWidgetBuilder separatorBuilder = null,
            int itemCount = 0,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            float? cacheExtent = null,
            ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual
        ) {
            return new ListView(
                key,
                scrollDirection,
                reverse,
                controller,
                primary,
                physics,
                shrinkWrap,
                padding,
                itemBuilder,
                separatorBuilder,
                itemCount,
                addAutomaticKeepAlives,
                addRepaintBoundaries,
                cacheExtent,
                keyboardDismissBehavior: keyboardDismissBehavior
            );
        }

        ListView(
            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,
            float? itemExtent = null,
            SliverChildDelegate childrenDelegate = null,
            float? cacheExtent = null
        ) : base(
            key: key,
            scrollDirection: scrollDirection,
            reverse: reverse,
            controller: controller,
            primary: primary,
            physics: physics,
            shrinkWrap: shrinkWrap,
            padding: padding,
            cacheExtent: cacheExtent
        ) {
            D.assert(childrenDelegate != null);
            this.itemExtent = itemExtent;
            this.childrenDelegate = childrenDelegate;
        }

        public static ListView custom(
            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,
            float? itemExtent = null,
            SliverChildDelegate childrenDelegate = null,
            float? cacheExtent = null
        ) {
            return new ListView(
                key,
                scrollDirection,
                reverse,
                controller,
                primary,
                physics,
                shrinkWrap,
                padding,
                itemExtent,
                childrenDelegate,
                cacheExtent);
        }

        public readonly float? itemExtent;

        public readonly SliverChildDelegate childrenDelegate;

        protected override Widget buildChildLayout(BuildContext context) {
            if (itemExtent != null) {
                return new SliverFixedExtentList(
                    del: childrenDelegate,
                    itemExtent: itemExtent.Value
                );
            }

            return new SliverList(del: childrenDelegate);
        }

        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
            base.debugFillProperties(properties);
            properties.add(new FloatProperty("itemExtent", itemExtent,
                defaultValue: foundation_.kNullDefaultValue));
        }

        static int _computeActualChildCount(int itemCount) {
            return Mathf.Max(0, itemCount * 2 - 1);
        }
    }

    public class GridView : BoxScrollView {
        public GridView(
            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,
            SliverGridDelegate gridDelegate = null,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            float? cacheExtent = null,
            List<Widget> children = null
        ) : base(
            key: key,
            scrollDirection: scrollDirection,
            reverse: reverse,
            controller: controller,
            primary: primary,
            physics: physics,
            shrinkWrap: shrinkWrap,
            padding: padding,
            cacheExtent: cacheExtent
        ) {
            D.assert(gridDelegate != null);
            childrenDelegate = new SliverChildListDelegate(
                children ?? new List<Widget>(),
                addAutomaticKeepAlives: addAutomaticKeepAlives,
                addRepaintBoundaries: addRepaintBoundaries
            );
        }

        public GridView(
            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,
            SliverGridDelegate gridDelegate = null,
            IndexedWidgetBuilder itemBuilder = null,
            int? itemCount = null,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            float? cacheExtent = null
        ) : base(
            key: key,
            scrollDirection: scrollDirection,
            reverse: reverse,
            controller: controller,
            primary: primary,
            physics: physics,
            shrinkWrap: shrinkWrap,
            padding: padding,
            cacheExtent: cacheExtent
        ) {
            this.gridDelegate = gridDelegate;
            childrenDelegate = new SliverChildBuilderDelegate(
                itemBuilder,
                childCount: itemCount,
                addAutomaticKeepAlives: addAutomaticKeepAlives,
                addRepaintBoundaries: addRepaintBoundaries
            );
        }

        public static GridView builder(
            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,
            SliverGridDelegate gridDelegate = null,
            IndexedWidgetBuilder itemBuilder = null,
            int? itemCount = null,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            float? cacheExtent = null
        ) {
            return new GridView(
                key: key,
                scrollDirection: scrollDirection,
                reverse: reverse,
                controller: controller,
                primary: primary,
                physics: physics,
                shrinkWrap: shrinkWrap,
                padding: padding,
                gridDelegate: gridDelegate,
                itemBuilder: itemBuilder,
                itemCount: itemCount,
                addAutomaticKeepAlives: addAutomaticKeepAlives,
                addRepaintBoundaries: addRepaintBoundaries,
                cacheExtent: cacheExtent
            );
        }

        public GridView(
            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,
            SliverGridDelegate gridDelegate = null,
            SliverChildDelegate childrenDelegate = null,
            float? cacheExtent = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start
        ) : base(
            key: key,
            scrollDirection: scrollDirection,
            reverse: reverse,
            controller: controller,
            primary: primary,
            physics: physics,
            shrinkWrap: shrinkWrap,
            padding: padding,
            cacheExtent: cacheExtent,
            dragStartBehavior: dragStartBehavior
        ) {
            D.assert(gridDelegate != null);
            D.assert(childrenDelegate != null);
            this.gridDelegate = gridDelegate;
            this.childrenDelegate = childrenDelegate;
        }

        public static GridView custom(
            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,
            SliverGridDelegate gridDelegate = null,
            SliverChildDelegate childrenDelegate = null,
            float? cacheExtent = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start
        ) {
            return new GridView(
                key: key,
                scrollDirection: scrollDirection,
                reverse: reverse,
                controller: controller,
                primary: primary,
                physics: physics,
                shrinkWrap: shrinkWrap,
                padding: padding,
                gridDelegate: gridDelegate,
                childrenDelegate: childrenDelegate,
                cacheExtent: cacheExtent,
                dragStartBehavior: dragStartBehavior
            );
        }

        public GridView(
            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,
            int? crossAxisCount = null,
            float mainAxisSpacing = 0.0f,
            float crossAxisSpacing = 0.0f,
            float childAspectRatio = 1.0f,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            float? cacheExtent = null,
            List<Widget> children = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start
        ) : base(
            key: key,
            scrollDirection: scrollDirection,
            reverse: reverse,
            controller: controller,
            primary: primary,
            physics: physics,
            shrinkWrap: shrinkWrap,
            padding: padding,
            cacheExtent: cacheExtent,
            dragStartBehavior: dragStartBehavior
        ) {
            gridDelegate = new SliverGridDelegateWithFixedCrossAxisCount(
                crossAxisCount: crossAxisCount ?? 0,
                mainAxisSpacing: mainAxisSpacing,
                crossAxisSpacing: crossAxisSpacing,
                childAspectRatio: childAspectRatio
            );
            childrenDelegate = new SliverChildListDelegate(
                children ?? new List<Widget>(),
                addAutomaticKeepAlives: addAutomaticKeepAlives,
                addRepaintBoundaries: addRepaintBoundaries
            );
        }

        public static GridView count(
            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,
            int? crossAxisCount = null,
            float mainAxisSpacing = 0.0f,
            float crossAxisSpacing = 0.0f,
            float childAspectRatio = 1.0f,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            float? cacheExtent = null,
            List<Widget> children = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start
        ) {
            return new GridView(
                key: key,
                scrollDirection: scrollDirection,
                reverse: reverse,
                controller: controller,
                primary: primary,
                physics: physics,
                shrinkWrap: shrinkWrap,
                padding: padding,
                crossAxisCount: crossAxisCount,
                mainAxisSpacing: mainAxisSpacing,
                crossAxisSpacing: crossAxisSpacing,
                childAspectRatio: childAspectRatio,
                addAutomaticKeepAlives: addAutomaticKeepAlives,
                addRepaintBoundaries: addRepaintBoundaries,
                cacheExtent: cacheExtent,
                children: children,
                dragStartBehavior: dragStartBehavior
            );
        }

        public GridView(
            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,
            float? maxCrossAxisExtent = null,
            float mainAxisSpacing = 0.0f,
            float crossAxisSpacing = 0.0f,
            float childAspectRatio = 1.0f,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            bool addSemanticIndexes = true,
            List<Widget> children = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start
        ) : base(
            key: key,
            scrollDirection: scrollDirection,
            reverse: reverse,
            controller: controller,
            primary: primary,
            physics: physics,
            shrinkWrap: shrinkWrap,
            padding: padding,
            dragStartBehavior: dragStartBehavior
        ) {
            gridDelegate = new SliverGridDelegateWithMaxCrossAxisExtent(
                maxCrossAxisExtent: maxCrossAxisExtent ?? 0,
                mainAxisSpacing: mainAxisSpacing,
                crossAxisSpacing: crossAxisSpacing,
                childAspectRatio: childAspectRatio
            );
            childrenDelegate = new SliverChildListDelegate(
                children ?? new List<Widget> { },
                addAutomaticKeepAlives: addAutomaticKeepAlives,
                addRepaintBoundaries: addRepaintBoundaries
            );
        }

        public static GridView extent(
            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,
            float? maxCrossAxisExtent = null,
            float mainAxisSpacing = 0.0f,
            float crossAxisSpacing = 0.0f,
            float childAspectRatio = 1.0f,
            bool addAutomaticKeepAlives = true,
            bool addRepaintBoundaries = true,
            List<Widget> children = null,
            DragStartBehavior dragStartBehavior = DragStartBehavior.start
        ) {
            return new GridView(
                key: key,
                scrollDirection: scrollDirection,
                reverse: reverse,
                controller: controller,
                primary: primary,
                physics: physics,
                shrinkWrap: shrinkWrap,
                padding: padding,
                maxCrossAxisExtent: maxCrossAxisExtent,
                mainAxisSpacing: mainAxisSpacing,
                crossAxisSpacing: crossAxisSpacing,
                childAspectRatio: childAspectRatio,
                addAutomaticKeepAlives: addAutomaticKeepAlives,
                addRepaintBoundaries: addRepaintBoundaries,
                children: children,
                dragStartBehavior: dragStartBehavior
            );
        }

        public readonly SliverGridDelegate gridDelegate;

        public readonly SliverChildDelegate childrenDelegate;

        protected override Widget buildChildLayout(BuildContext context) {
            return new SliverGrid(
                layoutDelegate: childrenDelegate,
                gridDelegate: gridDelegate
            );
        }
    }
}