fix sliver_layout

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

+using System.Collections.Generic;
+using Unity.UIWidgets.foundation;
+using Unity.UIWidgets.painting;
+using Unity.UIWidgets.rendering;
+using Unity.UIWidgets.ui;
+
+namespace Unity.UIWidgets.widgets {
+    public delegate Widget SliverLayoutWidgetBuilder(BuildContext context, SliverConstraints constraints) ;
+    
+    public class SliverLayoutBuilder : ConstrainedLayoutBuilder<SliverConstraints> {
+        public SliverLayoutBuilder(
+            Key key = null,
+            ConstraintBuilder builder = null
+        ) : base(key: key, builder: builder) {
+            
+        }
+
+        public static SliverLayoutBuilder Creat(
+            Key key = null,
+            SliverLayoutWidgetBuilder builder = null
+            ) {
+            ConstraintBuilder _builder = (context, constraints) => {
+                return builder(context, (SliverConstraints)constraints);
+            };
+            return new SliverLayoutBuilder(key,_builder);
+        }
+
+        public new SliverLayoutWidgetBuilder builder {
+            get {
+                //return base.builder;
+                SliverLayoutWidgetBuilder _builder = (context, constraints) => {
+                    return base.builder(context, (SliverConstraints) constraints);
+                };
+                return _builder;
+            }
+        }
+
+        public override RenderObject createRenderObject(BuildContext context) {
+            return new _RenderSliverLayoutBuilder();
+        }
+    }
+    public class _RenderSliverLayoutBuilder : RenderObjectWithChildMixinRenderSliver<RenderSliver>, RenderConstrainedLayoutBuilder<SliverConstraints, RenderSliver> { 
+        public override float? childMainAxisPosition(RenderObject child) {
+            D.assert(child != null);
+            D.assert(child == this.child);
+            return 0;
+        }
+
+        protected override void performLayout() {
+            layoutAndBuildChild();
+            child?.layout(constraints, parentUsesSize: true);
+            geometry = child?.geometry ?? SliverGeometry.zero;
+        }
+        public override void applyPaintTransform(RenderObject child, Matrix4 transform) {
+            D.assert(child != null);
+            D.assert(child == this.child);
+        }
+        public override void paint(PaintingContext context, Offset offset) {
+            if (child?.geometry?.visible == true)
+                context.paintChild(child, offset);
+        }
+
+        protected override bool hitTestChildren(SliverHitTestResult result,float mainAxisPosition = 0f, float crossAxisPosition = 0f) {
+            return child != null
+                   && child.geometry.hitTestExtent > 0
+                   && child.hitTest(result, mainAxisPosition: mainAxisPosition, crossAxisPosition: crossAxisPosition);
+        }
+
+        public bool debugValidateChild(RenderObject child) {
+            D.assert(() => {
+                if (!(child is RenderSliver)) {
+                    throw new UIWidgetsError(
+                        "A " + GetType() + " expected a child of type " + typeof(RenderSliver) + " but received a " +
+                        "child of type " + child.GetType() + ".\n" +
+                        "RenderObjects expect specific types of children because they " +
+                        "coordinate with their children during layout and paint. For " +
+                        "example, a RenderSliver cannot be the child of a RenderBox because " +
+                        "a RenderSliver does not understand the RenderBox layout protocol.\n" +
+                        "\n" +
+                        "The " + GetType() + " that expected a " + typeof(RenderSliver) + " child was created by:\n" +
+                        "  " + debugCreator + "\n" +
+                        "\n" +
+                        "The " + child.GetType() + " that did not match the expected child type " +
+                        "was created by:\n" +
+                        "  " + child.debugCreator + "\n"
+                    );
+                }
+
+                return true;
+            });
+            return true;
+        }
+
+        
+        internal RenderSliver _child;
+
+        public RenderSliver child {
+            get { return _child; }
+            set {
+                if (_child != null) {
+                    dropChild(_child);
+                }
+
+                _child = value;
+                if (_child != null) {
+                    adoptChild(_child);
+                }
+            }
+        }
+
+        RenderObject RenderObjectWithChildMixin.child {
+            get { return child; }
+            set { child = (RenderSliver)value; }
+        }
+
+        public LayoutCallback<SliverConstraints> _callback { get; set; }
+        public void updateCallback(LayoutCallback<SliverConstraints> value) {
+            if (value == _callback)
+                return;
+            _callback = value;
+            markNeedsLayout();
+        }
+
+        public void layoutAndBuildChild() {
+            D.assert(_callback != null);
+            invokeLayoutCallback(_callback);
+        }
+    }
+
+}