Dismissible RTL (#13137)

Fix the dismissible demo in the gallery (make it actuall update when you pick something from its menu; give it a better affordance for resetting once you've dismissed everything).

Improve some docs.

Fix various flinging bugs with dismissible. Add tests for those cases.

Add a feature to flutter_test to support a drag-then-fling gesture (used by the flinging tests).

examples/flutter_gallery/lib/demo/material/leave_behind_demo.dart

@@ -60,20 +60,22 @@ class LeaveBehindDemoState extends State<LeaveBehindDemo> {
   }
 
   void handleDemoAction(LeaveBehindDemoAction action) {
-    switch (action) {
-      case LeaveBehindDemoAction.reset:
-        initListItems();
-        break;
-      case LeaveBehindDemoAction.horizontalSwipe:
-        _dismissDirection = DismissDirection.horizontal;
-        break;
-      case LeaveBehindDemoAction.leftSwipe:
-        _dismissDirection = DismissDirection.endToStart;
-        break;
-      case LeaveBehindDemoAction.rightSwipe:
-        _dismissDirection = DismissDirection.startToEnd;
-        break;
-    }
+    setState(() {
+      switch (action) {
+        case LeaveBehindDemoAction.reset:
+          initListItems();
+          break;
+        case LeaveBehindDemoAction.horizontalSwipe:
+          _dismissDirection = DismissDirection.horizontal;
+          break;
+        case LeaveBehindDemoAction.leftSwipe:
+          _dismissDirection = DismissDirection.endToStart;
+          break;
+        case LeaveBehindDemoAction.rightSwipe:
+          _dismissDirection = DismissDirection.startToEnd;
+          break;
+      }
+    });
   }
 
   void handleUndo(LeaveBehindItem item) {
@@ -161,9 +163,16 @@ class LeaveBehindDemoState extends State<LeaveBehindDemo> {
           )
         ]
       ),
-      body: new ListView(
-        children: leaveBehindItems.map(buildItem).toList()
-      )
+      body: leaveBehindItems.isEmpty
+          ? new Center(
+              child: new RaisedButton(
+                onPressed: () => handleDemoAction(LeaveBehindDemoAction.reset),
+                child: const Text('Reset the list'),
+              ),
+            )
+          : new ListView(
+             children: leaveBehindItems.map(buildItem).toList()
+            ),
     );
   }
 }

packages/flutter/lib/src/widgets/dismissible.dart

@@ -6,6 +6,7 @@ import 'package:flutter/foundation.dart';
 
 import 'automatic_keep_alive.dart';
 import 'basic.dart';
+import 'debug.dart';
 import 'framework.dart';
 import 'gesture_detector.dart';
 import 'ticker_provider.dart';
@@ -114,12 +115,21 @@ class Dismissible extends StatefulWidget {
   /// immediately after the the widget is dismissed.
   final Duration resizeDuration;
 
-  /// The offset threshold the item has to be dragged in order to be considered dismissed.
+  /// The offset threshold the item has to be dragged in order to be considered
+  /// dismissed.
   ///
-  /// Represented as a fraction, e.g. if it is 0.4, then the item has to be dragged at least
-  /// 40% towards one direction to be considered dismissed. Clients can define different
-  /// thresholds for each dismiss direction. This allows for use cases where item can be
-  /// dismissed to end but not to start.
+  /// Represented as a fraction, e.g. if it is 0.4 (the default), then the item
+  /// has to be dragged at least 40% towards one direction to be considered
+  /// dismissed. Clients can define different thresholds for each dismiss
+  /// direction.
+  ///
+  /// Flinging is treated as being equivalent to dragging almost to 1.0, so
+  /// flinging can dismiss an item past any threshold less than 1.0.
+  ///
+  /// See also [direction], which controls the directions in which the items can
+  /// be dismissed. Setting a threshold of 1.0 (or greater) prevents a drag in
+  /// the given [DismissDirection] even if it would be allowed by the
+  /// [direction] property.
   final Map<DismissDirection, double> dismissThresholds;
 
   @override
@@ -165,6 +175,8 @@ class _DismissibleClipper extends CustomClipper<Rect> {
   }
 }
 
+enum _FlingGestureKind { none, forward, reverse }
+
 class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin, AutomaticKeepAliveClientMixin {
   @override
   void initState() {
@@ -200,15 +212,23 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
         || widget.direction == DismissDirection.startToEnd;
   }
 
-  DismissDirection get _dismissDirection {
-    if (_directionIsXAxis)
-      return  _dragExtent > 0 ? DismissDirection.startToEnd : DismissDirection.endToStart;
-    return _dragExtent > 0 ? DismissDirection.down : DismissDirection.up;
+  DismissDirection _extentToDirection(double extent) {
+    if (extent == 0.0)
+      return null;
+    if (_directionIsXAxis) {
+      switch (Directionality.of(context)) {
+        case TextDirection.rtl:
+          return extent < 0 ? DismissDirection.startToEnd : DismissDirection.endToStart;
+        case TextDirection.ltr:
+          return extent > 0 ? DismissDirection.startToEnd : DismissDirection.endToStart;
+      }
+      assert(false);
+      return null;
+    }
+    return extent > 0 ? DismissDirection.down : DismissDirection.up;
   }
 
-  double get _dismissThreshold {
-    return widget.dismissThresholds[_dismissDirection] ?? _kDismissThreshold;
-  }
+  DismissDirection get _dismissDirection => _extentToDirection(_dragExtent);
 
   bool get _isActive {
     return _dragUnderway || _moveController.isAnimating;
@@ -246,16 +266,40 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
         break;
 
       case DismissDirection.up:
-      case DismissDirection.endToStart:
         if (_dragExtent + delta < 0)
           _dragExtent += delta;
         break;
 
       case DismissDirection.down:
-      case DismissDirection.startToEnd:
         if (_dragExtent + delta > 0)
           _dragExtent += delta;
         break;
+
+      case DismissDirection.endToStart:
+        switch (Directionality.of(context)) {
+          case TextDirection.rtl:
+            if (_dragExtent + delta > 0)
+              _dragExtent += delta;
+            break;
+          case TextDirection.ltr:
+            if (_dragExtent + delta < 0)
+              _dragExtent += delta;
+            break;
+        }
+        break;
+
+      case DismissDirection.startToEnd:
+        switch (Directionality.of(context)) {
+          case TextDirection.rtl:
+            if (_dragExtent + delta < 0)
+              _dragExtent += delta;
+            break;
+          case TextDirection.ltr:
+            if (_dragExtent + delta > 0)
+              _dragExtent += delta;
+            break;
+        }
+        break;
     }
     if (oldDragExtent.sign != _dragExtent.sign) {
       setState(() {
@@ -275,35 +319,35 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
     ).animate(_moveController);
   }
 
-  bool _isFlingGesture(Velocity velocity) {
-    // Cannot fling an item if it cannot be dismissed by drag.
-    if (_dismissThreshold >= 1.0)
-      return false;
+  _FlingGestureKind _describeFlingGesture(Velocity velocity) {
+    assert(widget.direction != null);
+    if (_dragExtent == 0.0) {
+      // If it was a fling, then it was a fling that was let loose at the exact
+      // middle of the range (i.e. when there's no displacement). In that case,
+      // we assume that the user meant to fling it back to the center, as
+      // opposed to having wanted to drag it out one way, then fling it past the
+      // center and into and out the other side.
+      return _FlingGestureKind.none;
+    }
     final double vx = velocity.pixelsPerSecond.dx;
     final double vy = velocity.pixelsPerSecond.dy;
+    DismissDirection flingDirection;
+    // Verify that the fling is in the generally right direction and fast enough.
     if (_directionIsXAxis) {
-      if (vx.abs() - vy.abs() < _kMinFlingVelocityDelta)
-        return false;
-      switch (widget.direction) {
-        case DismissDirection.horizontal:
-          return vx.abs() > _kMinFlingVelocity;
-        case DismissDirection.endToStart:
-          return -vx > _kMinFlingVelocity;
-        default:
-          return vx > _kMinFlingVelocity;
-      }
+      if (vx.abs() - vy.abs() < _kMinFlingVelocityDelta || vx.abs() < _kMinFlingVelocity)
+        return _FlingGestureKind.none;
+      assert(vx != 0.0);
+      flingDirection = _extentToDirection(vx);
     } else {
-      if (vy.abs() - vx.abs() < _kMinFlingVelocityDelta)
-        return false;
-      switch (widget.direction) {
-        case DismissDirection.vertical:
-          return vy.abs() > _kMinFlingVelocity;
-        case DismissDirection.up:
-          return -vy > _kMinFlingVelocity;
-        default:
-          return vy > _kMinFlingVelocity;
-      }
+      if (vy.abs() - vx.abs() < _kMinFlingVelocityDelta || vy.abs() < _kMinFlingVelocity)
+        return _FlingGestureKind.none;
+      assert(vy != 0.0);
+      flingDirection = _extentToDirection(vy);
     }
+    assert(_dismissDirection != null);
+    if (flingDirection == _dismissDirection)
+      return _FlingGestureKind.forward;
+    return _FlingGestureKind.reverse;
   }
 
   void _handleDragEnd(DragEndDetails details) {
@@ -312,14 +356,35 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
     _dragUnderway = false;
     if (_moveController.isCompleted) {
       _startResizeAnimation();
-    } else if (_isFlingGesture(details.velocity)) {
-      final double flingVelocity = _directionIsXAxis ? details.velocity.pixelsPerSecond.dx : details.velocity.pixelsPerSecond.dy;
-      _dragExtent = flingVelocity.sign;
-      _moveController.fling(velocity: flingVelocity.abs() * _kFlingVelocityScale);
-    } else if (_moveController.value > _dismissThreshold) {
-      _moveController.forward();
-    } else {
-      _moveController.reverse();
+      return;
+    }
+    final double flingVelocity = _directionIsXAxis ? details.velocity.pixelsPerSecond.dx : details.velocity.pixelsPerSecond.dy;
+    switch (_describeFlingGesture(details.velocity)) {
+      case _FlingGestureKind.forward:
+        assert(_dragExtent != 0.0);
+        assert(!_moveController.isDismissed);
+        if ((widget.dismissThresholds[_dismissDirection] ?? _kDismissThreshold) >= 1.0) {
+          _moveController.reverse();
+          break;
+        }
+        _dragExtent = flingVelocity.sign;
+        _moveController.fling(velocity: flingVelocity.abs() * _kFlingVelocityScale);
+        break;
+      case _FlingGestureKind.reverse:
+        assert(_dragExtent != 0.0);
+        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[_dismissDirection] ?? _kDismissThreshold)) {
+            _moveController.forward();
+          } else {
+            _moveController.reverse();
+          }
+        }
+        break;
     }
   }
 
@@ -335,8 +400,11 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
     assert(_resizeController == null);
     assert(_sizePriorToCollapse == null);
     if (widget.resizeDuration == null) {
-      if (widget.onDismissed != null)
-        widget.onDismissed(_dismissDirection);
+      if (widget.onDismissed != null) {
+        final DismissDirection direction = _dismissDirection;
+        assert(direction != null);
+        widget.onDismissed(direction);
+      }
     } else {
       _resizeController = new AnimationController(duration: widget.resizeDuration, vsync: this)
         ..addListener(_handleResizeProgressChanged)
@@ -357,8 +425,11 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
 
   void _handleResizeProgressChanged() {
     if (_resizeController.isCompleted) {
-      if (widget.onDismissed != null)
-        widget.onDismissed(_dismissDirection);
+      if (widget.onDismissed != null) {
+        final DismissDirection direction = _dismissDirection;
+        assert(direction != null);
+        widget.onDismissed(direction);
+      }
     } else {
       if (widget.onResize != null)
         widget.onResize();
@@ -368,6 +439,9 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
   @override
   Widget build(BuildContext context) {
     super.build(context); // See AutomaticKeepAliveClientMixin.
+
+    assert(!_directionIsXAxis || debugCheckHasDirectionality(context));
+
     Widget background = widget.background;
     if (widget.secondaryBackground != null) {
       final DismissDirection direction = _dismissDirection;

packages/flutter/test/widgets/dismissible_test.dart

@@ -2,9 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
 
 const double itemExtent = 100.0;
 Axis scrollDirection = Axis.vertical;
@@ -13,9 +14,9 @@ DismissDirection reportedDismissDirection;
 List<int> dismissedItems = <int>[];
 Widget background;
 
-Widget buildTest({ double startToEndThreshold }) {
+Widget buildTest({ double startToEndThreshold, TextDirection textDirection: TextDirection.ltr }) {
   return new Directionality(
-    textDirection: TextDirection.ltr,
+    textDirection: textDirection,
     child: new StatefulBuilder(
       builder: (BuildContext context, StateSetter setState) {
         Widget buildDismissibleItem(int item) {
@@ -44,17 +45,14 @@ Widget buildTest({ double startToEndThreshold }) {
           );
         }
 
-        return new Directionality(
-          textDirection: TextDirection.ltr,
-          child: new Container(
-            padding: const EdgeInsets.all(10.0),
-            child: new ListView(
-              scrollDirection: scrollDirection,
-              itemExtent: itemExtent,
-              children: <int>[0, 1, 2, 3, 4]
-                .where((int i) => !dismissedItems.contains(i))
-                .map(buildDismissibleItem).toList(),
-            ),
+        return new Container(
+          padding: const EdgeInsets.all(10.0),
+          child: new ListView(
+            scrollDirection: scrollDirection,
+            itemExtent: itemExtent,
+            children: <int>[0, 1, 2, 3, 4]
+              .where((int i) => !dismissedItems.contains(i))
+              .map(buildDismissibleItem).toList(),
           ),
         );
       },
@@ -62,32 +60,30 @@ Widget buildTest({ double startToEndThreshold }) {
   );
 }
 
-Future<Null> dismissElement(WidgetTester tester, Finder finder, { DismissDirection gestureDirection }) async {
-  assert(tester.any(finder));
-  assert(gestureDirection != DismissDirection.horizontal);
-  assert(gestureDirection != DismissDirection.vertical);
+typedef Future<Null> DismissMethod(WidgetTester tester, Finder finder, { @required AxisDirection gestureDirection });
 
+Future<Null> dismissElement(WidgetTester tester, Finder finder, { @required AxisDirection gestureDirection }) async {
   Offset downLocation;
   Offset upLocation;
   switch (gestureDirection) {
-    case DismissDirection.endToStart:
+    case AxisDirection.left:
       // getTopRight() returns a point that's just beyond itemWidget's right
       // edge and outside the Dismissible event listener's bounds.
       downLocation = tester.getTopRight(finder) + const Offset(-0.1, 0.0);
       upLocation = tester.getTopLeft(finder);
       break;
-    case DismissDirection.startToEnd:
+    case AxisDirection.right:
       // we do the same thing here to keep the test symmetric
       downLocation = tester.getTopLeft(finder) + const Offset(0.1, 0.0);
       upLocation = tester.getTopRight(finder);
       break;
-    case DismissDirection.up:
+    case AxisDirection.up:
       // getBottomLeft() returns a point that's just below itemWidget's bottom
       // edge and outside the Dismissible event listener's bounds.
       downLocation = tester.getBottomLeft(finder) + const Offset(0.0, -0.1);
       upLocation = tester.getTopLeft(finder);
       break;
-    case DismissDirection.down:
+    case AxisDirection.down:
       // again with doing the same here for symmetry
       downLocation = tester.getTopLeft(finder) + const Offset(0.1, 0.0);
       upLocation = tester.getBottomLeft(finder);
@@ -96,19 +92,49 @@ Future<Null> dismissElement(WidgetTester tester, Finder finder, { DismissDirecti
       fail('unsupported gestureDirection');
   }
 
-  final TestGesture gesture = await tester.startGesture(downLocation, pointer: 5);
+  final TestGesture gesture = await tester.startGesture(downLocation);
   await gesture.moveTo(upLocation);
   await gesture.up();
 }
 
-Future<Null> dismissItem(WidgetTester tester, int item, { DismissDirection gestureDirection }) async {
-  assert(gestureDirection != DismissDirection.horizontal);
-  assert(gestureDirection != DismissDirection.vertical);
+Future<Null> flingElement(WidgetTester tester, Finder finder, { @required AxisDirection gestureDirection, double initialOffsetFactor: 0.0 }) async {
+  Offset delta;
+  switch (gestureDirection) {
+    case AxisDirection.left:
+      delta = const Offset(-300.0, 0.0);
+      break;
+    case AxisDirection.right:
+      delta = const Offset(300.0, 0.0);
+      break;
+    case AxisDirection.up:
+      delta = const Offset(0.0, -300.0);
+      break;
+    case AxisDirection.down:
+      delta = const Offset(0.0, 300.0);
+      break;
+    default:
+      fail('unsupported gestureDirection');
+  }
+  await tester.fling(finder, delta, 1000.0, initialOffset: delta * initialOffsetFactor);
+}
 
+Future<Null> flingElementFromZero(WidgetTester tester, Finder finder, { @required AxisDirection gestureDirection }) async {
+  // This is a special case where we drag in one direction, then fling back so
+  // that at the point of release, we're at exactly the point at which we
+  // started, but with velocity. This is needed to check a boundary coundition
+  // in the flinging behavior.
+  await flingElement(tester, finder, gestureDirection: gestureDirection, initialOffsetFactor: -1.0);
+}
+
+Future<Null> dismissItem(WidgetTester tester, int item, {
+  @required AxisDirection gestureDirection,
+  DismissMethod mechanism: dismissElement,
+}) async {
+  assert(gestureDirection != null);
   final Finder itemFinder = find.text(item.toString());
   expect(itemFinder, findsOneWidget);
 
-  await dismissElement(tester, itemFinder, gestureDirection: gestureDirection);
+  await mechanism(tester, itemFinder, gestureDirection: gestureDirection);
 
   await tester.pump(); // start the slide
   await tester.pump(const Duration(seconds: 1)); // finish the slide and start shrinking...
@@ -147,12 +173,56 @@ void main() {
     await tester.pumpWidget(buildTest());
     expect(dismissedItems, isEmpty);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.startToEnd);
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.right);
     expect(find.text('0'), findsNothing);
     expect(dismissedItems, equals(<int>[0]));
     expect(reportedDismissDirection, DismissDirection.startToEnd);
 
-    await dismissItem(tester, 1, gestureDirection: DismissDirection.endToStart);
+    await dismissItem(tester, 1, gestureDirection: AxisDirection.left);
+    expect(find.text('1'), findsNothing);
+    expect(dismissedItems, equals(<int>[0, 1]));
+    expect(reportedDismissDirection, DismissDirection.endToStart);
+  });
+
+  testWidgets('Horizontal fling triggers dismiss scrollDirection=vertical', (WidgetTester tester) async {
+    scrollDirection = Axis.vertical;
+    dismissDirection = DismissDirection.horizontal;
+
+    await tester.pumpWidget(buildTest());
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.right, mechanism: flingElement);
+    expect(find.text('0'), findsNothing);
+    expect(dismissedItems, equals(<int>[0]));
+    expect(reportedDismissDirection, DismissDirection.startToEnd);
+
+    await dismissItem(tester, 1, gestureDirection: AxisDirection.left, mechanism: flingElement);
+    expect(find.text('1'), findsNothing);
+    expect(dismissedItems, equals(<int>[0, 1]));
+    expect(reportedDismissDirection, DismissDirection.endToStart);
+  });
+
+  testWidgets('Horizontal fling does not trigger at zero offset, but does otherwise', (WidgetTester tester) async {
+    scrollDirection = Axis.vertical;
+    dismissDirection = DismissDirection.horizontal;
+
+    await tester.pumpWidget(buildTest(startToEndThreshold: 0.95));
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.right, mechanism: flingElementFromZero);
+    expect(find.text('0'), findsOneWidget);
+    expect(dismissedItems, equals(<int>[]));
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.left, mechanism: flingElementFromZero);
+    expect(find.text('0'), findsOneWidget);
+    expect(dismissedItems, equals(<int>[]));
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.right, mechanism: flingElement);
+    expect(find.text('0'), findsNothing);
+    expect(dismissedItems, equals(<int>[0]));
+    expect(reportedDismissDirection, DismissDirection.startToEnd);
+
+    await dismissItem(tester, 1, gestureDirection: AxisDirection.left, mechanism: flingElement);
     expect(find.text('1'), findsNothing);
     expect(dismissedItems, equals(<int>[0, 1]));
     expect(reportedDismissDirection, DismissDirection.endToStart);
@@ -165,49 +235,151 @@ void main() {
     await tester.pumpWidget(buildTest());
     expect(dismissedItems, isEmpty);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.up);
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.up);
     expect(find.text('0'), findsNothing);
     expect(dismissedItems, equals(<int>[0]));
     expect(reportedDismissDirection, DismissDirection.up);
 
-    await dismissItem(tester, 1, gestureDirection: DismissDirection.down);
+    await dismissItem(tester, 1, gestureDirection: AxisDirection.down);
     expect(find.text('1'), findsNothing);
     expect(dismissedItems, equals(<int>[0, 1]));
     expect(reportedDismissDirection, DismissDirection.down);
   });
 
-  testWidgets('drag-left with DismissDirection.left triggers dismiss', (WidgetTester tester) async {
+  testWidgets('drag-left with DismissDirection.endToStart triggers dismiss (LTR)', (WidgetTester tester) async {
     scrollDirection = Axis.vertical;
     dismissDirection = DismissDirection.endToStart;
 
     await tester.pumpWidget(buildTest());
     expect(dismissedItems, isEmpty);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.startToEnd);
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.right);
     expect(find.text('0'), findsOneWidget);
     expect(dismissedItems, isEmpty);
-    await dismissItem(tester, 1, gestureDirection: DismissDirection.startToEnd);
+    await dismissItem(tester, 1, gestureDirection: AxisDirection.right);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.endToStart);
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.left);
     expect(find.text('0'), findsNothing);
     expect(dismissedItems, equals(<int>[0]));
-    await dismissItem(tester, 1, gestureDirection: DismissDirection.endToStart);
+    await dismissItem(tester, 1, gestureDirection: AxisDirection.left);
   });
 
-  testWidgets('drag-right with DismissDirection.right triggers dismiss', (WidgetTester tester) async {
+  testWidgets('drag-right with DismissDirection.startToEnd triggers dismiss (LTR)', (WidgetTester tester) async {
     scrollDirection = Axis.vertical;
     dismissDirection = DismissDirection.startToEnd;
 
     await tester.pumpWidget(buildTest());
     expect(dismissedItems, isEmpty);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.endToStart);
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.left);
+    expect(find.text('0'), findsOneWidget);
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.right);
+    expect(find.text('0'), findsNothing);
+    expect(dismissedItems, equals(<int>[0]));
+  });
+
+  testWidgets('drag-right with DismissDirection.endToStart triggers dismiss (RTL)', (WidgetTester tester) async {
+    scrollDirection = Axis.vertical;
+    dismissDirection = DismissDirection.endToStart;
+
+    await tester.pumpWidget(buildTest(textDirection: TextDirection.rtl));
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.left);
+    expect(find.text('0'), findsOneWidget);
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.right);
+    expect(find.text('0'), findsNothing);
+    expect(dismissedItems, equals(<int>[0]));
+  });
+
+  testWidgets('drag-left with DismissDirection.startToEnd triggers dismiss (RTL)', (WidgetTester tester) async {
+    scrollDirection = Axis.vertical;
+    dismissDirection = DismissDirection.startToEnd;
+
+    await tester.pumpWidget(buildTest(textDirection: TextDirection.rtl));
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.right);
     expect(find.text('0'), findsOneWidget);
     expect(dismissedItems, isEmpty);
+    await dismissItem(tester, 1, gestureDirection: AxisDirection.right);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.startToEnd);
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.left);
     expect(find.text('0'), findsNothing);
     expect(dismissedItems, equals(<int>[0]));
+    await dismissItem(tester, 1, gestureDirection: AxisDirection.left);
+  });
+
+  testWidgets('fling-left with DismissDirection.endToStart triggers dismiss (LTR)', (WidgetTester tester) async {
+    scrollDirection = Axis.vertical;
+    dismissDirection = DismissDirection.endToStart;
+
+    await tester.pumpWidget(buildTest());
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.right);
+    expect(find.text('0'), findsOneWidget);
+    expect(dismissedItems, isEmpty);
+    await dismissItem(tester, 1, gestureDirection: AxisDirection.right);
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.left);
+    expect(find.text('0'), findsNothing);
+    expect(dismissedItems, equals(<int>[0]));
+    await dismissItem(tester, 1, gestureDirection: AxisDirection.left);
+  });
+
+  testWidgets('fling-right with DismissDirection.startToEnd triggers dismiss (LTR)', (WidgetTester tester) async {
+    scrollDirection = Axis.vertical;
+    dismissDirection = DismissDirection.startToEnd;
+
+    await tester.pumpWidget(buildTest());
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.left);
+    expect(find.text('0'), findsOneWidget);
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.right);
+    expect(find.text('0'), findsNothing);
+    expect(dismissedItems, equals(<int>[0]));
+  });
+
+  testWidgets('fling-right with DismissDirection.endToStart triggers dismiss (RTL)', (WidgetTester tester) async {
+    scrollDirection = Axis.vertical;
+    dismissDirection = DismissDirection.endToStart;
+
+    await tester.pumpWidget(buildTest(textDirection: TextDirection.rtl));
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.left);
+    expect(find.text('0'), findsOneWidget);
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.right);
+    expect(find.text('0'), findsNothing);
+    expect(dismissedItems, equals(<int>[0]));
+  });
+
+  testWidgets('fling-left with DismissDirection.startToEnd triggers dismiss (RTL)', (WidgetTester tester) async {
+    scrollDirection = Axis.vertical;
+    dismissDirection = DismissDirection.startToEnd;
+
+    await tester.pumpWidget(buildTest(textDirection: TextDirection.rtl));
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.right);
+    expect(find.text('0'), findsOneWidget);
+    expect(dismissedItems, isEmpty);
+    await dismissItem(tester, 1, mechanism: flingElement, gestureDirection: AxisDirection.right);
+
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.left);
+    expect(find.text('0'), findsNothing);
+    expect(dismissedItems, equals(<int>[0]));
+    await dismissItem(tester, 1, mechanism: flingElement, gestureDirection: AxisDirection.left);
   });
 
   testWidgets('drag-up with DismissDirection.up triggers dismiss', (WidgetTester tester) async {
@@ -217,11 +389,11 @@ void main() {
     await tester.pumpWidget(buildTest());
     expect(dismissedItems, isEmpty);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.down);
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.down);
     expect(find.text('0'), findsOneWidget);
     expect(dismissedItems, isEmpty);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.up);
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.up);
     expect(find.text('0'), findsNothing);
     expect(dismissedItems, equals(<int>[0]));
   });
@@ -233,11 +405,43 @@ void main() {
     await tester.pumpWidget(buildTest());
     expect(dismissedItems, isEmpty);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.up);
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.up);
+    expect(find.text('0'), findsOneWidget);
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.down);
+    expect(find.text('0'), findsNothing);
+    expect(dismissedItems, equals(<int>[0]));
+  });
+
+  testWidgets('fling-up with DismissDirection.up triggers dismiss', (WidgetTester tester) async {
+    scrollDirection = Axis.horizontal;
+    dismissDirection = DismissDirection.up;
+
+    await tester.pumpWidget(buildTest());
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.down);
+    expect(find.text('0'), findsOneWidget);
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.up);
+    expect(find.text('0'), findsNothing);
+    expect(dismissedItems, equals(<int>[0]));
+  });
+
+  testWidgets('fling-down with DismissDirection.down triggers dismiss', (WidgetTester tester) async {
+    scrollDirection = Axis.horizontal;
+    dismissDirection = DismissDirection.down;
+
+    await tester.pumpWidget(buildTest());
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.up);
     expect(find.text('0'), findsOneWidget);
     expect(dismissedItems, isEmpty);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.down);
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.down);
     expect(find.text('0'), findsNothing);
     expect(dismissedItems, equals(<int>[0]));
   });
@@ -249,11 +453,27 @@ void main() {
     await tester.pumpWidget(buildTest(startToEndThreshold: 1.0));
     expect(dismissedItems, isEmpty);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.startToEnd);
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.right);
+    expect(find.text('0'), findsOneWidget);
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, gestureDirection: AxisDirection.left);
+    expect(find.text('0'), findsNothing);
+    expect(dismissedItems, equals(<int>[0]));
+  });
+
+  testWidgets('fling-left has no effect on dismissible with a high dismiss threshold', (WidgetTester tester) async {
+    scrollDirection = Axis.vertical;
+    dismissDirection = DismissDirection.horizontal;
+
+    await tester.pumpWidget(buildTest(startToEndThreshold: 1.0));
+    expect(dismissedItems, isEmpty);
+
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.right);
     expect(find.text('0'), findsOneWidget);
     expect(dismissedItems, isEmpty);
 
-    await dismissItem(tester, 0, gestureDirection: DismissDirection.endToStart);
+    await dismissItem(tester, 0, mechanism: flingElement, gestureDirection: AxisDirection.left);
     expect(find.text('0'), findsNothing);
     expect(dismissedItems, equals(<int>[0]));
   });
@@ -309,12 +529,12 @@ void main() {
     );
     expect(find.text('1'), findsOneWidget);
     expect(find.text('2'), findsOneWidget);
-    await dismissElement(tester, find.text('2'), gestureDirection: DismissDirection.startToEnd);
+    await dismissElement(tester, find.text('2'), gestureDirection: AxisDirection.right);
     await tester.pump(); // start the slide away
     await tester.pump(const Duration(seconds: 1)); // finish the slide away
     expect(find.text('1'), findsOneWidget);
     expect(find.text('2'), findsNothing);
-    await dismissElement(tester, find.text('1'), gestureDirection: DismissDirection.startToEnd);
+    await dismissElement(tester, find.text('1'), gestureDirection: AxisDirection.right);
     await tester.pump(); // start the slide away
     await tester.pump(const Duration(seconds: 1)); // finish the slide away (at which point the child is no longer included in the tree)
     expect(find.text('1'), findsNothing);
@@ -331,7 +551,7 @@ void main() {
 
     final Finder itemFinder = find.text('0');
     expect(itemFinder, findsOneWidget);
-    await dismissElement(tester, itemFinder, gestureDirection: DismissDirection.startToEnd);
+    await dismissElement(tester, itemFinder, gestureDirection: AxisDirection.right);
     await tester.pump();
 
     expect(find.text('background'), findsOneWidget); // The other four have been culled.

packages/flutter_test/lib/src/controller.dart

@@ -299,11 +299,28 @@ class WidgetController {
   ///
   /// A fling is essentially a drag that ends at a particular speed. If you
   /// just want to drag and end without a fling, use [drag].
+  ///
+  /// The `initialOffset` argument, if non-zero, causes the pointer to first
+  /// apply that offset, then pump a delay of `initialOffsetDelay`. This can be
+  /// used to simulate a drag followed by a fling, including dragging in the
+  /// opposite direction of the fling (e.g. dragging 200 pixels to the right,
+  /// then fling to the left over 200 pixels, ending at the exact point that the
+  /// drag started).
   Future<Null> fling(Finder finder, Offset offset, double speed, {
     int pointer,
     Duration frameInterval: const Duration(milliseconds: 16),
+    Offset initialOffset: Offset.zero,
+    Duration initialOffsetDelay: const Duration(seconds: 1),
   }) {
-    return flingFrom(getCenter(finder), offset, speed, pointer: pointer, frameInterval: frameInterval);
+    return flingFrom(
+      getCenter(finder),
+      offset,
+      speed,
+      pointer: pointer,
+      frameInterval: frameInterval,
+      initialOffset: initialOffset,
+      initialOffsetDelay: initialOffsetDelay,
+    );
   }
 
   /// Attempts a fling gesture starting from the given location, moving the
@@ -324,7 +341,19 @@ class WidgetController {
   ///
   /// A fling is essentially a drag that ends at a particular speed. If you
   /// just want to drag and end without a fling, use [dragFrom].
-  Future<Null> flingFrom(Offset startLocation, Offset offset, double speed, { int pointer, Duration frameInterval: const Duration(milliseconds: 16) }) {
+  ///
+  /// The `initialOffset` argument, if non-zero, causes the pointer to first
+  /// apply that offset, then pump a delay of `initialOffsetDelay`. This can be
+  /// used to simulate a drag followed by a fling, including dragging in the
+  /// opposite direction of the fling (e.g. dragging 200 pixels to the right,
+  /// then fling to the left over 200 pixels, ending at the exact point that the
+  /// drag started).
+  Future<Null> flingFrom(Offset startLocation, Offset offset, double speed, {
+    int pointer,
+    Duration frameInterval: const Duration(milliseconds: 16),
+    Offset initialOffset: Offset.zero,
+    Duration initialOffsetDelay: const Duration(seconds: 1),
+  }) {
     assert(offset.distance > 0.0);
     assert(speed > 0.0); // speed is pixels/second
     return TestAsyncUtils.guard(() async {
@@ -335,8 +364,13 @@ class WidgetController {
       double timeStamp = 0.0;
       double lastTimeStamp = timeStamp;
       await sendEventToBinding(testPointer.down(startLocation, timeStamp: new Duration(milliseconds: timeStamp.round())), result);
+      if (initialOffset.distance > 0.0) {
+        await sendEventToBinding(testPointer.move(startLocation + initialOffset, timeStamp: new Duration(milliseconds: timeStamp.round())), result);
+        timeStamp += initialOffsetDelay.inMilliseconds;
+        await pump(initialOffsetDelay);
+      }
       for (int i = 0; i <= kMoveCount; i += 1) {
-        final Offset location = startLocation + Offset.lerp(Offset.zero, offset, i / kMoveCount);
+        final Offset location = startLocation + initialOffset + Offset.lerp(Offset.zero, offset, i / kMoveCount);
         await sendEventToBinding(testPointer.move(location, timeStamp: new Duration(milliseconds: timeStamp.round())), result);
         timeStamp += timeStampDelta;
         if (timeStamp - lastTimeStamp > frameInterval.inMilliseconds) {