Convert Dismissable to use gestures

Convert Dismissable to use the ScrollStart, ScrollUpdate, and ScrollEnd gestures. Support for fling gestures is TBD.

Included a basic unit test that checks that one item can be dismissed with a press-drag-release gesture.

Fixed the scroll gesture recognizer: if the last pointer goes up and candidate recognizers still exist, then reject the gesture.

packages/flutter/lib/gestures/scroll.dart

@@ -76,6 +76,10 @@ abstract class _ScrollGestureRecognizer<T extends dynamic> extends GestureRecogn
   }
 
   void didStopTrackingLastPointer() {
+    if (_state == ScrollState.possible) {
+      resolve(GestureDisposition.rejected);
+      return;
+    }
     bool wasAccepted = (_state == ScrollState.accepted);
     _state = ScrollState.ready;
     if (wasAccepted && onEnd != null)

packages/flutter/lib/widgets/dismissable.dart

@@ -10,6 +10,7 @@ import 'package:sky/animation/curves.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/transitions.dart';
 import 'package:sky/widgets/framework.dart';
+import 'package:sky/widgets/gesture_detector.dart';
 
 const Duration _kCardDismissFadeout = const Duration(milliseconds: 200);
 const Duration _kCardDismissResize = const Duration(milliseconds: 300);
@@ -99,45 +100,33 @@ class Dismissable extends StatefulComponent {
       _maybeCallOnResized();
   }
 
-  EventDisposition _handlePointerDown(sky.PointerEvent event) {
+  void _handleScrollStart() {
     if (_fadePerformance.isAnimating)
-      return EventDisposition.processed;
-
+      return;
     _dragUnderway = true;
     _dragX = 0.0;
     _fadePerformance.progress = 0.0;
-    return EventDisposition.processed;
   }
 
-  EventDisposition _handlePointerMove(sky.PointerEvent event) {
-    if (!_isActive)
-      return EventDisposition.ignored;
-
-    if (_fadePerformance.isAnimating)
-      return EventDisposition.processed;
-
+  void _handleScrollUpdate(double scrollOffset) {
+    if (!_isActive || _fadePerformance.isAnimating)
+      return;
     double oldDragX = _dragX;
-    _dragX += event.dx;
+    _dragX -= scrollOffset;
     if (oldDragX.sign != _dragX.sign)
       setState(() {}); // Rebuild to update the new drag endpoint.
     if (!_fadePerformance.isAnimating)
       _fadePerformance.progress = _dragX.abs() / (_size.width * _kDismissCardThreshold);
-    return EventDisposition.processed;
   }
 
-  EventDisposition _handlePointerUpOrCancel(_) {
-    if (!_isActive)
-      return EventDisposition.ignored;
-
-    if (_fadePerformance.isAnimating)
-      return EventDisposition.processed;
-
+  _handleScrollEnd() {
+    if (!_isActive || _fadePerformance.isAnimating)
+      return;
     _dragUnderway = false;
     if (_fadePerformance.isCompleted)
       _startResizePerformance();
     else if (!_fadePerformance.isAnimating)
       _fadePerformance.reverse();
-    return EventDisposition.processed;
   }
 
   bool _isHorizontalFlingGesture(sky.GestureEvent event) {
@@ -185,22 +174,23 @@ class Dismissable extends StatefulComponent {
         height: dismissHeight);
     }
 
-    return new Listener(
-      onPointerDown: _handlePointerDown,
-      onPointerMove: _handlePointerMove,
-      onPointerUp: _handlePointerUpOrCancel,
-      onPointerCancel: _handlePointerUpOrCancel,
-      onGestureFlingStart: _handleFlingStart,
-      child: new SizeObserver(
-        callback: _handleSizeChanged,
-        child: new FadeTransition(
-          performance: _fadePerformance,
-          onCompleted: _handleFadeCompleted,
-          opacity: new AnimatedValue<double>(1.0, end: 0.0),
-          child: new SlideTransition(
+    return new GestureDetector(
+      onHorizontalScrollStart: _handleScrollStart,
+      onHorizontalScrollUpdate: _handleScrollUpdate,
+      onHorizontalScrollEnd: _handleScrollEnd,
+      child: new Listener(
+        onGestureFlingStart: _handleFlingStart,
+        child: new SizeObserver(
+          callback: _handleSizeChanged,
+          child: new FadeTransition(
             performance: _fadePerformance,
-            position: new AnimatedValue<Point>(Point.origin, end: _activeCardDragEndPoint),
-            child: child
+            onCompleted: _handleFadeCompleted,
+            opacity: new AnimatedValue<double>(1.0, end: 0.0),
+            child: new SlideTransition(
+              performance: _fadePerformance,
+              position: new AnimatedValue<Point>(Point.origin, end: _activeCardDragEndPoint),
+              child: child
+            )
           )
         )
       )

packages/unit/test/widget/dismissable_test.dart

+import 'package:quiver/testing/async.dart';
+import 'package:sky/widgets.dart';
+import 'package:test/test.dart';
+
+import '../engine/mock_events.dart';
+import 'widget_tester.dart';
+
+void main() {
+  test('Horizontal drag triggers dismiss', () {
+    WidgetTester tester = new WidgetTester();
+    TestPointer pointer = new TestPointer(5);
+
+    const double itemHeight = 50.0;
+    List<int> dismissedItems = [];
+
+    void handleOnResized(item) {
+      expect(dismissedItems.contains(item), isFalse);
+    }
+
+    void handleOnDismissed(item) {
+      expect(dismissedItems.contains(item), isFalse);
+      dismissedItems.add(item);
+    }
+
+    Widget buildDismissableItem(int item) {
+      return new Dismissable(
+        key: new ValueKey<int>(item),
+        onDismissed: () { handleOnDismissed(item); },
+        onResized: () { handleOnResized(item); },
+        child: new Container(
+          height: itemHeight,
+          child: new Text(item.toString())
+        )
+      );
+    }
+
+    Widget builder() {
+      return new Container(
+        padding: const EdgeDims.all(10.0),
+        child: new ScrollableList<int>(
+          items: [0, 1, 2, 3, 4, 5],
+          itemBuilder: buildDismissableItem,
+          scrollDirection: ScrollDirection.vertical,
+          itemExtent: itemHeight
+        )
+      );
+    }
+
+    tester.pumpFrame(builder);
+    Widget item3 = tester.findText("3");
+    expect(item3, isNotNull);
+    expect(dismissedItems, isEmpty);
+
+    // Gesture: press-drag-release from the Dismissable's top-left corner
+    // to its top-right corner. Triggers the resize animation which concludes
+    // by calling onDismissed().
+    Point downLocation = tester.getTopLeft(item3);
+    Point upLocation = tester.getTopRight(item3);
+    tester.dispatchEvent(pointer.down(downLocation), downLocation);
+    tester.dispatchEvent(pointer.move(upLocation), upLocation);
+    tester.dispatchEvent(pointer.up(), upLocation);
+
+    new FakeAsync().run((async) {
+      tester.pumpFrame(builder); // start the resize animation
+      tester.pumpFrame(builder, 1000.0); // finish the resize animation
+      async.elapse(new Duration(seconds: 1));
+      tester.pumpFrame(builder, 2000.0); // dismiss
+      async.elapse(new Duration(seconds: 1));
+      expect(dismissedItems, equals([3]));
+      expect(tester.findText("3"), isNull);
+    });
+
+  });
+}

packages/unit/test/widget/widget_tester.dart

@@ -83,6 +83,20 @@ class WidgetTester {
     return box.localToGlobal(box.size.center(Point.origin));
   }
 
+  Point getTopLeft(Widget widget) {
+    assert(widget != null);
+    RenderBox box = widget.renderObject as RenderBox;
+    assert(box != null);
+    return box.localToGlobal(Point.origin);
+  }
+
+  Point getTopRight(Widget widget) {
+    assert(widget != null);
+    RenderBox box = widget.renderObject as RenderBox;
+    assert(box != null);
+    return box.localToGlobal(box.size.topRight(Point.origin));
+  }
+
   HitTestResult _hitTest(Point location) => SkyBinding.instance.hitTest(location);
 
   EventDisposition _dispatchEvent(sky.Event event, HitTestResult result) {