Add an AnimationStatus to AnimationPerformance, and use that in Drawer,

SnackBar, and PopupMenu instead of custom statuses.

packages/flutter/example/stocks/lib/stock_home.dart

@@ -27,7 +27,7 @@ class StockHome extends StatefulComponent {
   bool _isSearching = false;
   String _searchQuery;
 
-  SnackBarStatus _snackBarStatus = SnackBarStatus.inactive;
+  AnimationStatus _snackBarStatus = AnimationStatus.dismissed;
   bool _isSnackBarShowing = false;
 
   void _handleSearchBegin() {
@@ -59,28 +59,28 @@ class StockHome extends StatefulComponent {
   }
 
   bool _drawerShowing = false;
-  DrawerStatus _drawerStatus = DrawerStatus.inactive;
+  AnimationStatus _drawerStatus = AnimationStatus.dismissed;
 
   void _handleOpenDrawer() {
     setState(() {
       _drawerShowing = true;
-      _drawerStatus = DrawerStatus.active;
+      _drawerStatus = AnimationStatus.forward;
     });
   }
 
-  void _handleDrawerStatusChange(DrawerStatus status) {
+  void _handleDrawerStatusChange(AnimationStatus status) {
     setState(() {
       _drawerStatus = status;
     });
   }
 
   bool _menuShowing = false;
-  PopupMenuStatus _menuStatus = PopupMenuStatus.inactive;
+  AnimationStatus _menuStatus = AnimationStatus.dismissed;
 
   void _handleMenuShow() {
     setState(() {
       _menuShowing = true;
-      _menuStatus = PopupMenuStatus.active;
+      _menuStatus = AnimationStatus.forward;
     });
   }
 
@@ -90,7 +90,7 @@ class StockHome extends StatefulComponent {
     });
   }
 
-  void _handleMenuStatusChanged(PopupMenuStatus status) {
+  void _handleMenuStatusChanged(AnimationStatus status) {
     setState(() {
       _menuStatus = status;
     });
@@ -112,7 +112,7 @@ class StockHome extends StatefulComponent {
   }
 
   Drawer buildDrawer() {
-    if (_drawerStatus == DrawerStatus.inactive)
+    if (_drawerStatus == AnimationStatus.dismissed)
       return null;
     assert(_drawerShowing); // TODO(mpcomplete): this is always true
     return new Drawer(
@@ -246,7 +246,7 @@ class StockHome extends StatefulComponent {
   }
 
   Widget buildSnackBar() {
-    if (_snackBarStatus == SnackBarStatus.inactive)
+    if (_snackBarStatus == AnimationStatus.dismissed)
       return null;
     return new SnackBar(
       showing: _isSnackBarShowing,
@@ -259,7 +259,7 @@ class StockHome extends StatefulComponent {
   void _handleStockPurchased() {
     setState(() {
       _isSnackBarShowing = true;
-      _snackBarStatus = SnackBarStatus.active;
+      _snackBarStatus = AnimationStatus.forward;
     });
   }
 
@@ -272,7 +272,7 @@ class StockHome extends StatefulComponent {
   }
 
   void addMenuToOverlays(List<Widget> overlays) {
-    if (_menuStatus == PopupMenuStatus.inactive)
+    if (_menuStatus == AnimationStatus.dismissed)
       return;
     overlays.add(new ModalOverlay(
       children: [new StockMenu(

packages/flutter/lib/animation/animation_performance.dart

@@ -8,6 +8,18 @@ import 'package:sky/animation/animated_value.dart';
 import 'package:sky/animation/forces.dart';
 import 'package:sky/animation/timeline.dart';
 
+enum AnimationDirection {
+  forward,
+  reverse
+}
+
+enum AnimationStatus {
+  dismissed, // stoped at 0
+  forward,   // animating from 0 => 1
+  reverse,   // animating from 1 => 0
+  completed, // stopped at 1
+}
+
 // This class manages a "performance" - a collection of values that change
 // based on a timeline. For example, a performance may handle an animation
 // of a menu opening by sliding and fading in (changing Y value and opacity)
@@ -16,30 +28,49 @@ import 'package:sky/animation/timeline.dart';
 // manipulating |progress|, or |fling| the timeline causing a physics-based
 // simulation to take over the progression.
 class AnimationPerformance {
-  AnimationPerformance() {
+  AnimationPerformance({this.variable, this.duration}) {
     _timeline = new Timeline(_tick);
   }
 
   AnimatedVariable variable;
-  // TODO(mpcomplete): duration should be on a director.
   Duration duration;
 
   // Advances from 0 to 1. On each tick, we'll update our variable's values.
   Timeline _timeline;
   Timeline get timeline => _timeline;
 
+  AnimationDirection _direction;
+  AnimationDirection get direction => _direction;
+
   double get progress => timeline.value;
   void set progress(double t) {
+    // TODO(mpcomplete): should this affect |direction|?
     stop();
     timeline.value = t.clamp(0.0, 1.0);
+    _checkStatusChanged();
   }
 
-  bool get isDismissed => progress == 0.0;
-  bool get isCompleted => progress == 1.0;
+  bool get isDismissed => status == AnimationStatus.dismissed;
+  bool get isCompleted => status == AnimationStatus.completed;
   bool get isAnimating => timeline.isAnimating;
 
-  Future play() => _animateTo(1.0);
-  Future reverse() => _animateTo(0.0);
+  AnimationStatus get status {
+    if (!isAnimating && progress == 1.0)
+      return AnimationStatus.completed;
+    if (!isAnimating && progress == 0.0)
+      return AnimationStatus.dismissed;
+    return direction == AnimationDirection.forward ?
+        AnimationStatus.forward :
+        AnimationStatus.reverse;
+  }
+
+  Future play([AnimationDirection direction = AnimationDirection.forward]) {
+    _direction = direction;
+    return resume();
+  }
+  Future forward() => play(AnimationDirection.forward);
+  Future reverse() => play(AnimationDirection.reverse);
+  Future resume() => _animateTo(direction == AnimationDirection.forward ? 1.0 : 0.0);
 
   void stop() {
     timeline.stop();
@@ -51,6 +82,9 @@ class AnimationPerformance {
   Future fling({double velocity: 1.0, Force force}) {
     if (force == null)
       force = kDefaultSpringForce;
+    // This is an approximation - the force may not necessarily result in
+    // animating the same direction as the initial velocity.
+    _direction = velocity >= 0.0 ? AnimationDirection.forward : AnimationDirection.reverse;
     return timeline.fling(force.release(progress, velocity));
   }
 
@@ -70,6 +104,27 @@ class AnimationPerformance {
       listener();
   }
 
+  final List<Function> _statusListeners = new List<Function>();
+
+  void addStatusListener(Function listener) {
+    _statusListeners.add(listener);
+  }
+
+  void removeStatusListener(Function listener) {
+    _statusListeners.remove(listener);
+  }
+
+  AnimationStatus _lastStatus = AnimationStatus.dismissed;
+  void _checkStatusChanged() {
+    AnimationStatus currentStatus = status;
+    if (currentStatus != _lastStatus) {
+      List<Function> localListeners = new List<Function>.from(_statusListeners);
+      for (Function listener in localListeners)
+        listener(currentStatus);
+    }
+    _lastStatus = currentStatus;
+  }
+
   Future _animateTo(double target) {
     double remainingDistance = (target - timeline.value).abs();
     timeline.stop();
@@ -81,5 +136,6 @@ class AnimationPerformance {
   void _tick(double t) {
     variable.setProgress(t);
     _notifyListeners();
+    _checkStatusChanged();
   }
 }

packages/flutter/lib/widgets/drawer.dart

@@ -15,6 +15,8 @@ import 'package:sky/widgets/scrollable_viewport.dart';
 import 'package:sky/widgets/theme.dart';
 import 'package:vector_math/vector_math.dart';
 
+export 'package:sky/animation/animation_performance.dart' show AnimationStatus;
+
 // TODO(eseidel): Draw width should vary based on device size:
 // http://www.google.com/design/spec/layout/structure.html#structure-side-nav
 
@@ -35,14 +37,7 @@ const Duration _kBaseSettleDuration = const Duration(milliseconds: 246);
 const Point _kOpenPosition = Point.origin;
 const Point _kClosedPosition = const Point(-_kWidth, 0.0);
 
-typedef void DrawerStatusChangeHandler (bool showing);
-
-enum DrawerStatus {
-  active,
-  inactive,
-}
-
-typedef void DrawerStatusChangedCallback(DrawerStatus status);
+typedef void DrawerStatusChangedCallback(AnimationStatus status);
 
 class Drawer extends AnimatedComponent {
   Drawer({
@@ -70,7 +65,7 @@ class Drawer extends AnimatedComponent {
     _performance = new AnimationPerformance()
       ..duration = _kBaseSettleDuration
       ..variable = new AnimatedList([_position, _maskColor])
-      ..addListener(_checkForStateChanged);
+      ..addStatusListener(_onStatusChanged);
     watch(_performance);
     if (showing)
       _show();
@@ -137,11 +132,8 @@ class Drawer extends AnimatedComponent {
 
   double get xPosition => _position.value.x;
 
-  DrawerStatus _lastStatus;
-  void _checkForStateChanged() {
-    DrawerStatus status = _status;
-    if (_lastStatus != null && status != _lastStatus) {
-      if (status == DrawerStatus.inactive &&
+  void _onStatusChanged(AnimationStatus status) {
+    if (status == AnimationStatus.dismissed &&
         navigator != null &&
         navigator.currentRoute is RouteState &&
         (navigator.currentRoute as RouteState).owner == this) // TODO(ianh): remove cast once analyzer is cleverer
@@ -149,10 +141,7 @@ class Drawer extends AnimatedComponent {
     if (onStatusChanged != null)
       onStatusChanged(status);
   }
-    _lastStatus = status;
-  }
 
-  DrawerStatus get _status => _performance.isDismissed ? DrawerStatus.inactive : DrawerStatus.active;
   bool get _isMostlyClosed => xPosition <= -_kWidth/2;
 
   void _settle() => _fling(_isMostlyClosed ? -1.0 : 1.0);

packages/flutter/lib/widgets/popup_menu.dart

@@ -16,6 +16,8 @@ import 'package:sky/widgets/navigator.dart';
 import 'package:sky/widgets/popup_menu_item.dart';
 import 'package:sky/widgets/scrollable_viewport.dart';
 
+export 'package:sky/animation/animation_performance.dart' show AnimationStatus;
+
 const Duration _kMenuDuration = const Duration(milliseconds: 300);
 double _kMenuCloseIntervalEnd = 2.0 / 3.0;
 const double _kMenuWidthStep = 56.0;
@@ -25,12 +27,7 @@ const double _kMenuMaxWidth = 5.0 * _kMenuWidthStep;
 const double _kMenuHorizontalPadding = 16.0;
 const double _kMenuVerticalPadding = 8.0;
 
-enum PopupMenuStatus {
-  active,
-  inactive,
-}
-
-typedef void PopupMenuStatusChangedCallback(PopupMenuStatus status);
+typedef void PopupMenuStatusChangedCallback(AnimationStatus status);
 
 class PopupMenu extends AnimatedComponent {
 
@@ -59,7 +56,7 @@ class PopupMenu extends AnimatedComponent {
   void initState() {
     _performance = new AnimationPerformance()
       ..duration = _kMenuDuration
-      ..addListener(_checkForStateChanged);
+      ..addStatusListener(_onStatusChanged);
     _updateAnimationVariables();
     watch(_performance);
     _updateBoxPainter();
@@ -115,13 +112,8 @@ class PopupMenu extends AnimatedComponent {
       boxShadow: shadows[level]));
   }
 
-  PopupMenuStatus get _status => _opacity.value != 0.0 ? PopupMenuStatus.active : PopupMenuStatus.inactive;
-
-  PopupMenuStatus _lastStatus;
-  void _checkForStateChanged() {
-    PopupMenuStatus status = _status;
-    if (_lastStatus != null && status != _lastStatus) {
-      if (status == PopupMenuStatus.inactive &&
+  void _onStatusChanged(AnimationStatus status) {
+    if (status == AnimationStatus.dismissed &&
         navigator != null &&
         navigator.currentRoute is RouteState &&
         (navigator.currentRoute as RouteState).owner == this) // TODO(ianh): remove cast once analyzer is cleverer
@@ -129,8 +121,6 @@ class PopupMenu extends AnimatedComponent {
     if (onStatusChanged != null)
       onStatusChanged(status);
   }
-    _lastStatus = status;
-  }
 
 
   void _open() {

packages/flutter/lib/widgets/snack_bar.dart

@@ -14,15 +14,11 @@ import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/default_text_style.dart';
 import 'package:sky/widgets/material.dart';
 import 'package:sky/widgets/theme.dart';
-
 import 'package:vector_math/vector_math.dart';
 
-enum SnackBarStatus {
-  active,
-  inactive,
-}
+export 'package:sky/animation/animation_performance.dart' show AnimationStatus;
 
-typedef void SnackBarStatusChangedCallback(SnackBarStatus status);
+typedef void SnackBarStatusChangedCallback(AnimationStatus status);
 
 const Duration _kSlideInDuration = const Duration(milliseconds: 200);
 
@@ -48,53 +44,35 @@ class SnackBarAction extends Component {
 
 // TODO(mpcomplete): generalize this to a SlideIn class.
 class SnackBarSlideInIntention extends AnimationIntention {
-  SnackBarSlideInIntention(this.duration, this.onStatusChanged);
+  SnackBarSlideInIntention(Duration duration) {
+    _position = new AnimatedValue<Point>(const Point(0.0, 50.0), end: Point.origin);
+    performance = new AnimationPerformance(duration: duration, variable: _position);
+  }
 
-  Duration duration;
   SnackBarStatusChangedCallback onStatusChanged;
   AnimatedValue<Point> _position;
-  AnimationPerformance _performance;
+  AnimationPerformance performance;
 
   void initFields(AnimatedContainer container) {
-    _position = new AnimatedValue<Point>(new Point(0.0, 50.0), end: Point.origin);
-    _performance = new AnimationPerformance()
-      ..duration = _kSlideInDuration
-      ..variable = _position
-      ..addListener(() { _updateProgress(container); });
-    _performance.progress = 0.0;
+    performance.addListener(() { _updateProgress(container); });
+    performance.progress = 0.0;
     if (container.tag)
-      _show();
+      performance.play();
   }
 
   void syncFields(AnimatedContainer original, AnimatedContainer updated) {
     if (original.tag != updated.tag) {
       original.tag = updated.tag;
-      original.tag ? _show() : _hide();
-    }
+      performance.play(original.tag ? AnimationDirection.forward : AnimationDirection.reverse);
     }
-
-  void _show() {
-    _performance.play();
-  }
-
-  void _hide() {
-    _performance.reverse();
   }
 
-  SnackBarStatus _lastStatus;
   void _updateProgress(AnimatedContainer container) {
     container.setState(() {
       container.transform = new Matrix4.identity()
         ..translate(_position.value.x, _position.value.y);
     });
-
-    SnackBarStatus status = _status;
-    if (_lastStatus != null && status != _lastStatus && onStatusChanged != null)
-      scheduleMicrotask(() { onStatusChanged(status); });
-    _lastStatus = status;
   }
-
-  SnackBarStatus get _status => _performance.isDismissed ? SnackBarStatus.inactive : SnackBarStatus.active;
 }
 
 class SnackBar extends StatefulComponent {
@@ -117,7 +95,8 @@ class SnackBar extends StatefulComponent {
   SnackBarSlideInIntention _intention;
 
   void initState() {
-    _intention = new SnackBarSlideInIntention(_kSlideInDuration, onStatusChanged);
+    _intention = new SnackBarSlideInIntention(_kSlideInDuration);
+    _intention.performance.addStatusListener(_onStatusChanged);
   }
 
   void syncFields(SnackBar source) {
@@ -127,6 +106,11 @@ class SnackBar extends StatefulComponent {
     showing = source.showing;
   }
 
+  void _onStatusChanged(AnimationStatus status) {
+    if (onStatusChanged != null)
+      scheduleMicrotask(() { onStatusChanged(status); });
+  }
+
   Widget build() {
     List<Widget> children = [
       new Flexible(