fix dismissible bug

Samples/UIWidgetsSamples_2019_4/Assets/MaterialSample/MaterialTabBarSample.cs

 using Unity.UIWidgets.painting;
 using Unity.UIWidgets.ui;
 using Unity.UIWidgets.widgets;
-using UnityEngine;
 using ui_ = Unity.UIWidgets.widgets.ui_;
 
 namespace UIWidgetsSample {

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

             }
 
             _dragUnderway = false;
-            _confirmStartResizeAnimation().then_((value) => {
-                if (_moveController.isCompleted && value) {
-                    _startResizeAnimation();
-                }
-                else {
-                    float flingVelocity = _directionIsXAxis
-                        ? details.velocity.pixelsPerSecond.dx
-                        : details.velocity.pixelsPerSecond.dy;
-                    switch (_describeFlingGesture(details.velocity)) {
-                        case _FlingGestureKind.forward:
-                            D.assert(_dragExtent != 0.0f);
-                            D.assert(!_moveController.isDismissed);
-                            if ((widget.dismissThresholds.getOrDefault(_dismissDirection) ??
-                                 _kDismissThreshold) >= 1.0) {
-                                _moveController.reverse();
-                                break;
-                            }
+            if (_moveController.isCompleted) {
+                _confirmStartResizeAnimation().then_((value) => {
+                    if (value) {
+                        _startResizeAnimation();
+                        return;
+                    }
+                });
+            }
-                            _dragExtent = flingVelocity.sign();
-                            _moveController.fling(velocity: flingVelocity.abs() * _kFlingVelocityScale);
-                            break;
-                        case _FlingGestureKind.reverse:
-                            D.assert(_dragExtent != 0.0f);
-                            D.assert(!_moveController.isDismissed);
-                            _dragExtent = flingVelocity.sign();
-                            _moveController.fling(velocity: -flingVelocity.abs() * _kFlingVelocityScale);
-                            break;
-                        case _FlingGestureKind.none:
-                            if (!_moveController.isDismissed) {
-                                // we already know it's not completed, we check that above
-                                if (_moveController.value >
-                                    (widget.dismissThresholds.getOrDefault(_dismissDirection) ??
-                                     _kDismissThreshold)) {
-                                    _moveController.forward();
-                                }
-                                else {
-                                    _moveController.reverse();
-                                }
-                            }
+            float flingVelocity = _directionIsXAxis
+                ? details.velocity.pixelsPerSecond.dx
+                : details.velocity.pixelsPerSecond.dy;
+            switch (_describeFlingGesture(details.velocity)) {
+                case _FlingGestureKind.forward:
+                    D.assert(_dragExtent != 0.0f);
+                    D.assert(!_moveController.isDismissed);
+                    if ((widget.dismissThresholds.getOrDefault(_dismissDirection) ??
+                         _kDismissThreshold) >= 1.0) {
+                        _moveController.reverse();
+                        break;
+                    }
-                            break;
+                    _dragExtent = flingVelocity.sign();
+                    _moveController.fling(velocity: flingVelocity.abs() * _kFlingVelocityScale);
+                    break;
+                case _FlingGestureKind.reverse:
+                    D.assert(_dragExtent != 0.0f);
+                    D.assert(!_moveController.isDismissed);
+                    _dragExtent = flingVelocity.sign();
+                    _moveController.fling(velocity: -flingVelocity.abs() * _kFlingVelocityScale);
+                    break;
+                case _FlingGestureKind.none:
+                    if (!_moveController.isDismissed) {
+                        // we already know it's not completed, we check that above
+                        if (_moveController.value >
+                            (widget.dismissThresholds.getOrDefault(_dismissDirection) ??
+                             _kDismissThreshold)) {
+                            _moveController.forward();
+                        }
+                        else {
+                            _moveController.reverse();
+                        }
-                }
-            });
+
+                    break;
+            }
         }
 
         void _handleDismissStatusChanged(AnimationStatus status) {
                 D.assert(() => {
                     if (_resizeAnimation.status != AnimationStatus.forward) {
                         D.assert(_resizeAnimation.status == AnimationStatus.completed);
-                        throw new UIWidgetsError(new List<DiagnosticsNode>{
+                        throw new UIWidgetsError(new List<DiagnosticsNode> {
                             new ErrorSummary("A dismissed Dismissible widget is still part of the tree."),
                             new ErrorHint(
                                 "Make sure to implement the onDismissed handler and to immediately remove the Dismissible " +
 
                 children.Add(content);
                 content = new Stack(children: children);
-                
             }
 
             return new GestureDetector(

Samples/UIWidgetsSamples_2019_4/Assets/MaterialSample/NavigatorPopSample.cs

+using System.Collections.Generic;
+using Unity.UIWidgets.async2;
+using Unity.UIWidgets.engine2;
+using Unity.UIWidgets.material;
+using Unity.UIWidgets.painting;
+using Unity.UIWidgets.rendering;
+using Unity.UIWidgets.widgets;
+
+namespace UIWidgetsSample
+{
+    public class NavigatorPopSample : UIWidgetsPanel
+    {
+        protected override void main()
+        {
+            ui_.runApp(new MaterialApp(
+                title: "Returning Data",
+                home: new PopDemo()));
+        }
+
+        protected new void OnEnable()
+        {
+            base.OnEnable();
+        }
+    }
+
+    public class PopDemo : StatelessWidget
+    {
+        public override Widget build(BuildContext context)
+        {
+            return new Scaffold(
+                appBar: new AppBar(
+                    title: new Text("Returning Data Demo")
+                ),
+                body: new Center(child: new SelectionButton())
+            );
+        }
+    }
+
+    internal class SelectionButton : StatelessWidget
+    {
+        public override Widget build(BuildContext context)
+        {
+            return new RaisedButton(
+                onPressed: () => { _navigateAndDisplaySelection(context); },
+                child: new Text("Pick an option, any option!")
+            );
+        }
+
+        // A method that launches the SelectionScreen and awaits the result from
+        // Navigator.pop!
+        private void _navigateAndDisplaySelection(BuildContext context)
+        {
+            // Navigator.push returns a Future that will complete after we call
+            // Navigator.pop on the Selection Screen!
+            Future<bool> result = Navigator.push<bool>(
+                context,
+                new MaterialPageRoute(builder: (subContext) => new SelectionScreen())
+            );
+
+            // After the Selection Screen returns a result, show it in a Snackbar!
+            result.then(value =>
+            {
+                bool res = (bool) value;
+                Scaffold
+                    .of(context)
+                    .showSnackBar(new SnackBar(content: new Text($"{res}")));
+            });
+        }
+    }
+
+    internal class SelectionScreen : StatelessWidget
+    {
+        public override Widget build(BuildContext context)
+        {
+            return new Scaffold(
+                appBar: new AppBar(
+                    title: new Text("Pick an option")
+                ),
+                body: new Center(
+                    child: new Column(
+                        mainAxisAlignment: MainAxisAlignment.center,
+                        children: new List<Widget>
+                        {
+                            new Padding(
+                                padding: EdgeInsets.all(8.0f),
+                                child: new RaisedButton(
+                                    onPressed: () =>
+                                    {
+                                        // Close the screen and return "Yep!" as the result
+                                        Navigator.pop(context, true);
+                                    },
+                                    child: new Text("Yep!")
+                                )
+                            ),
+                            new Padding(
+                                padding: EdgeInsets.all(8.0f),
+                                child: new RaisedButton(
+                                    onPressed: () =>
+                                    {
+                                        // Close the screen and return "Nope!" as the result
+                                        Navigator.pop(context, false);
+                                    },
+                                    child: new Text("Nope.")
+                                )
+                            )
+                        }
+                    )
+                )
+            );
+        }
+    }
+}