Card "swipe-away" dismiss

sky/sdk/example/widgets/card_collection.dart

Index: sky/sdk/example/widgets/card_collection.dart
diff --git a/sky/sdk/example/widgets/card_collection.dart b/sky/sdk/example/widgets/card_collection.dart
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@@ -0,0 +1,166 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:sky' as sky;
+
+import 'package:vector_math/vector_math.dart';
+import 'package:sky/animation/animation_performance.dart';
+import 'package:sky/base/lerp.dart';
+import 'package:sky/painting/text_style.dart';
+import 'package:sky/theme/colors.dart';
+import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/card.dart';
+import 'package:sky/widgets/scaffold.dart';
+import 'package:sky/widgets/theme.dart';
+import 'package:sky/widgets/tool_bar.dart';
+import 'package:sky/widgets/widget.dart';
+
+
+const int _kCardDismissFadeoutMS = 300;
+const double _kMinCardFlingVelocity = 0.4;
+const double _kDismissCardThreshold = 0.70;
+
+class CardCollectionApp extends App {
+
+  final TextStyle cardLabelStyle =
+    new TextStyle(color: White, fontSize: 18.0, fontWeight: bold);
+
+  CardCollectionApp() {
+    _activeCardAnimation = new AnimationPerformance()
+      ..variable = new AnimatedType(0.0, 1.0)
+      ..duration = new Duration(milliseconds: _kCardDismissFadeoutMS);
+    _activeCardAnimation.timeline.onValueChanged.listen(_handleAnimationProgressChanged);
+  }
+
+  int _activeCardIndex = -1;
+  double _activeCardAnchorX;
+  AnimationPerformance _activeCardAnimation;
+  double _activeCardWidth;
+  bool _activeCardDragUnderway = false;
+  Set<int> _dismissedCardIndices = new Set<int>();
+
+  double get _activeCardOpacity => 1.0 - _activeCardAnimation.progress;
+
+  double get _activeCardOffset {
+    return _activeCardAnimation.progress * _activeCardWidth * _kDismissCardThreshold;
+  }
+
+  void _handleAnimationProgressChanged(_) {
+    setState(() {
+      if (_activeCardAnimation.isCompleted && !_activeCardDragUnderway)

[Matt Perry, 2015/07/08 22:21:59]

would this be simpler if AnimationPerformance supplied an "animationComplete"
callback?

[hansmuller, 2015/07/08 23:07:15]

I'm not sure. I'd still need to add a callback with 
activeCardAnimation.timeline.onValueChanged.listen(), since dragging a card
updates the progress property (which defines the cards opacity and translation).
Dragging the card can cause the animation to "complete" repeatedly.  I could
write:

activeCardAnimation.timeline.onValueChanged.listen(scheduleBuild);

- and - 

activeCardAnimation.onCompleted = (_) {
  setState(() {                                
    if (!_activeCardDragUnderway)
      _dismissedCardIndices.add(_activeCardIndex);
   })
}

I guess that doesn't seem clearer.

+        _dismissedCardIndices.add(_activeCardIndex);
+    });
+  }
+
+  void _handleSizeChanged(Size newSize) {
+    _activeCardWidth = newSize.width;
+  }
+
+  void _handlePointerDown(sky.PointerEvent event, int cardIndex) {
+    setState(() {
+      _activeCardIndex = cardIndex;
+      _activeCardDragUnderway = true;
+      _activeCardAnchorX = null;
+      _activeCardAnimation.progress = 0.0;
+    });
+  }
+
+  void _handlePointerMove(sky.PointerEvent event) {
+    if (_activeCardWidth == null || _activeCardIndex < 0)
+      return;
+
+    if (_activeCardAnchorX == null)
+      _activeCardAnchorX = event.x - event.dx;

[abarth-chromium, 2015/07/08 21:12:02]

Unfortunately, the dx property gives you the delta since the last event, not the
total delta since the down.

[hansmuller, 2015/07/08 21:22:50]

I assumed that, in this case, the last event was the pointer-down. I verified as
much experimentally :-).

In my next CL I'll just accumulate event.dx values. And I'll allow one to
dismiss to the left or right.

+
+    setState(() {
+      double eventOffsetX = event.x - _activeCardAnchorX;
+      if (!_activeCardAnimation.isAnimating)
+        _activeCardAnimation.progress = eventOffsetX / (_activeCardWidth * _kDismissCardThreshold);
+    });
+  }
+
+  void _handlePointerUpOrCancel(_) {
+    if (_activeCardWidth == null || _activeCardIndex < 0)
+      return;
+
+    setState(() {
+      _activeCardDragUnderway = false;
+      if (_activeCardAnimation.isCompleted)
+        _dismissedCardIndices.add(_activeCardIndex);
+      else if (!_activeCardAnimation.isAnimating)
+        _activeCardAnimation.progress = 0.0;
+    });
+  }
+
+  void _handleFlingStart(sky.GestureEvent event) {
+    if (_activeCardWidth == null || _activeCardIndex < 0)
+      return;
+
+    _activeCardDragUnderway = false;
+    double velocityX = event.velocityX / 1000;
+    if (velocityX.abs() >= _kMinCardFlingVelocity)
+      _activeCardAnimation.fling(velocity: velocityX / _activeCardWidth);
+  }
+
+  Widget _buildCard(int index, Color color) {
+    Widget label = new Center(child: new Text("Item ${index}", style: cardLabelStyle));
+    Widget card = new Card(
+      child: new Padding(child: label, padding: const EdgeDims.all(8.0)),
+      color: color
+    );
+
+    if (index == _activeCardIndex && _activeCardOffset > 0.0) {
+      Matrix4 transform = new Matrix4.identity();

[Matt Perry, 2015/07/08 22:21:59]

This'll get a little nicer once I check in my AnimatedContainer:
https://codereview.chromium.org/1223073002/

+      transform.translate(_activeCardOffset, 0.0);
+      card = new Transform(child: card, transform: transform);
+      if (_activeCardAnimation != null)
+        card = new Opacity(child: card, opacity: _activeCardOpacity);
+    }
+
+    return new Listener(
+      child: card,
+      onPointerDown: (event) { _handlePointerDown(event, index); }
+    );
+  }
+
+  Widget _buildCardCollection(List<double> heights) {
+    List<Widget> items = <Widget>[];
+    for(int index = 0; index < heights.length; index++) {
+      if (_dismissedCardIndices.contains(index))
+        continue;
+      Color color = lerpColor(Red[500], Blue[500], index / heights.length);
+      items.add(new Container(
+        child: _buildCard(index, color),
+        height: heights[index]
+      ));
+    }
+
+    Widget collection = new Container(
+      child: new SizeObserver(child: new Block(items), callback: _handleSizeChanged),
+      padding: const EdgeDims.symmetric(vertical: 12.0, horizontal: 8.0),
+      decoration: new BoxDecoration(backgroundColor: Theme.of(this).primarySwatch[50])
+    );
+
+    return new Listener(
+      child: collection,
+      onPointerMove: _handlePointerMove,
+      onPointerUp: _handlePointerUpOrCancel,
+      onPointerCancel: _handlePointerUpOrCancel,
+      onGestureFlingStart: _handleFlingStart
+    );
+  }
+
+  Widget build() {
+    return new Scaffold(
+      toolbar: new ToolBar(center: new Text('Swipe Away')),
+      body: _buildCardCollection(
+          [48.0, 64.0, 82.0, 46.0, 60.0, 55.0, 84.0, 96.0, 50.0,
+           48.0, 64.0, 82.0, 46.0, 60.0, 55.0, 84.0, 96.0, 50.0])
+    );
+  }
+}
+
+void main() {
+  runApp(new CardCollectionApp());
+}