Remove AnimationDirection

This concept is now private to AnimationController. All the clients actually
want the AnimationStatus.

examples/material_gallery/lib/demo/progress_indicator_demo.dart

@@ -14,39 +14,44 @@ class _ProgressIndicatorDemoState extends State<ProgressIndicatorDemo> {
     super.initState();
     controller = new AnimationController(
       duration: const Duration(milliseconds: 1500)
-    )..play(AnimationDirection.forward);
+    )..forward();
 
     animation = new CurvedAnimation(
       parent: controller,
       curve: new Interval(0.0, 0.9, curve: Curves.ease),
       reverseCurve: Curves.ease
     )..addStatusListener((AnimationStatus status) {
-      if (status == AnimationStatus.dismissed || status == AnimationStatus.completed)
-        reverseValueAnimationDirection();
+      if (status == AnimationStatus.dismissed)
+        controller.forward();
+      else if (status == AnimationStatus.completed)
+        controller.reverse();
     });
   }
 
   Animation<double> animation;
   AnimationController controller;
 
-  void handleTap() {
+  void _handleTap() {
     setState(() {
       // valueAnimation.isAnimating is part of our build state
-      if (controller.isAnimating)
+      if (controller.isAnimating) {
         controller.stop();
-      else
-        controller.resume();
+      } else {
+        switch (controller.status) {
+          case AnimationStatus.dismissed:
+          case AnimationStatus.forward:
+            controller.forward();
+            break;
+          case AnimationStatus.reverse:
+          case AnimationStatus.completed:
+            controller.reverse();
+            break;
+        }
+      }
     });
   }
 
-  void reverseValueAnimationDirection() {
-    AnimationDirection direction = (controller.direction == AnimationDirection.forward)
-      ? AnimationDirection.reverse
-      : AnimationDirection.forward;
-    controller.play(direction);
-  }
-
-  Widget buildIndicators(BuildContext context, Widget child) {
+  Widget _buildIndicators(BuildContext context, Widget child) {
     List<Widget> indicators = <Widget>[
         new SizedBox(
           width: 200.0,
@@ -82,13 +87,13 @@ class _ProgressIndicatorDemoState extends State<ProgressIndicatorDemo> {
       body: new DefaultTextStyle(
         style: Theme.of(context).text.title,
         child: new GestureDetector(
-          onTap: handleTap,
+          onTap: _handleTap,
           behavior: HitTestBehavior.opaque,
           child: new Container(
             padding: const EdgeDims.symmetric(vertical: 12.0, horizontal: 8.0),
             child: new AnimatedBuilder(
               animation: animation,
-              builder: buildIndicators
+              builder: _buildIndicators
             )
           )
         )

packages/flutter/lib/src/animation/animation.dart

@@ -4,15 +4,6 @@
 
 import 'dart:ui' show Color, Size, Rect, VoidCallback;
 
-/// The direction in which an animation is running.
-enum AnimationDirection {
-  /// The animation is running from beginning to end.
-  forward,
-
-  /// The animation is running backwards, from end to beginning.
-  reverse
-}
-
 /// The status of an animation
 enum AnimationStatus {
   /// The animation is stopped at the beginning
@@ -62,9 +53,6 @@ abstract class Animation<T> {
   /// The current status of this animation.
   AnimationStatus get status;
 
-  /// The current direction of the animation.
-  AnimationDirection get direction;
-
   /// The current value of the animation.
   T get value;
 
@@ -79,7 +67,6 @@ abstract class Animation<T> {
   }
   String toStringDetails() {
     assert(status != null);
-    assert(direction != null);
     String icon;
     switch (status) {
       case AnimationStatus.forward:
@@ -89,24 +76,10 @@ abstract class Animation<T> {
         icon = '\u25C0'; // <
         break;
       case AnimationStatus.completed:
-        switch (direction) {
-          case AnimationDirection.forward:
-            icon = '\u23ED'; // >>|
-            break;
-          case AnimationDirection.reverse:
-            icon = '\u29CF'; // <|
-            break;
-        }
+        icon = '\u23ED'; // >>|
         break;
       case AnimationStatus.dismissed:
-        switch (direction) {
-          case AnimationDirection.forward:
-            icon = '\u29D0'; // |>
-            break;
-          case AnimationDirection.reverse:
-            icon = '\u23EE'; // |<<
-            break;
-        }
+        icon = '\u23EE'; // |<<
         break;
     }
     assert(icon != null);

packages/flutter/lib/src/animation/animation_controller.dart

@@ -13,6 +13,15 @@ import 'curves.dart';
 import 'forces.dart';
 import 'listener_helpers.dart';
 
+/// The direction in which an animation is running.
+enum _AnimationDirection {
+  /// The animation is running from beginning to end.
+  forward,
+
+  /// The animation is running backwards, from end to beginning.
+  reverse
+}
+
 /// A controller for an animation.
 ///
 /// An animation controller can drive an animation forward or backward and can
@@ -79,9 +88,6 @@ class AnimationController extends Animation<double>
   /// The length of time this animation should last.
   Duration duration;
 
-  AnimationDirection get direction => _direction;
-  AnimationDirection _direction = AnimationDirection.forward;
-
   Ticker _ticker;
   Simulation _simulation;
 
@@ -106,31 +112,28 @@ class AnimationController extends Animation<double>
   /// Whether this animation is currently animating in either the forward or reverse direction.
   bool get isAnimating => _ticker.isTicking;
 
+  _AnimationDirection _direction;
+
   AnimationStatus get status {
     if (!isAnimating && value == upperBound)
       return AnimationStatus.completed;
     if (!isAnimating && value == lowerBound)
       return AnimationStatus.dismissed;
-    return _direction == AnimationDirection.forward ?
+    return _direction == _AnimationDirection.forward ?
         AnimationStatus.forward :
         AnimationStatus.reverse;
   }
 
   /// Starts running this animation forwards (towards the end).
-  Future forward() => play(AnimationDirection.forward);
-
-  /// Starts running this animation in reverse (towards the beginning).
-  Future reverse() => play(AnimationDirection.reverse);
-
-  /// Starts running this animation in the given direction.
-  Future play(AnimationDirection direction) {
-    _direction = direction;
-    return resume();
+  Future forward() {
+    _direction = _AnimationDirection.forward;
+    return animateTo(upperBound);
   }
 
-  /// Resumes this animation in the most recent direction.
-  Future resume() {
-    return animateTo(_direction == AnimationDirection.forward ? upperBound : lowerBound);
+  /// Starts running this animation in reverse (towards the beginning).
+  Future reverse() {
+    _direction = _AnimationDirection.reverse;
+    return animateTo(lowerBound);
   }
 
   /// Drives the animation from its current value to target.
@@ -165,7 +168,7 @@ class AnimationController extends Animation<double>
   /// animation will complete, otherwise it will dismiss.
   Future fling({ double velocity: 1.0, Force force }) {
     force ??= kDefaultSpringForce;
-    _direction = velocity < 0.0 ? AnimationDirection.reverse : AnimationDirection.forward;
+    _direction = velocity < 0.0 ? _AnimationDirection.reverse : _AnimationDirection.forward;
     return animateWith(force.release(value, velocity));
   }
 

packages/flutter/lib/src/animation/animations.dart

@@ -16,7 +16,6 @@ class _AlwaysCompleteAnimation extends Animation<double> {
   void addStatusListener(AnimationStatusListener listener) { }
   void removeStatusListener(AnimationStatusListener listener) { }
   AnimationStatus get status => AnimationStatus.completed;
-  AnimationDirection get direction => AnimationDirection.forward;
   double get value => 1.0;
 }
 
@@ -35,7 +34,6 @@ class _AlwaysDismissedAnimation extends Animation<double> {
   void addStatusListener(AnimationStatusListener listener) { }
   void removeStatusListener(AnimationStatusListener listener) { }
   AnimationStatus get status => AnimationStatus.dismissed;
-  AnimationDirection get direction => AnimationDirection.forward;
   double get value => 0.0;
 }
 
@@ -57,7 +55,6 @@ class AlwaysStoppedAnimation<T> extends Animation<T> {
   void addStatusListener(AnimationStatusListener listener) { }
   void removeStatusListener(AnimationStatusListener listener) { }
   AnimationStatus get status => AnimationStatus.forward;
-  AnimationDirection get direction => AnimationDirection.forward;
 }
 
 /// Implements most of the [Animation] interface, by deferring its behavior to a
@@ -77,7 +74,6 @@ abstract class AnimationWithParentMixin<T> {
   void removeStatusListener(AnimationStatusListener listener) => parent.removeStatusListener(listener);
 
   AnimationStatus get status => parent.status;
-  AnimationDirection get direction => parent.direction;
 }
 
 /// An animation that is a proxy for another animation.
@@ -92,13 +88,11 @@ class ProxyAnimation extends Animation<double>
     _parent = animation;
     if (_parent == null) {
       _status = AnimationStatus.dismissed;
-      _direction = AnimationDirection.forward;
       _value = 0.0;
     }
   }
 
   AnimationStatus _status;
-  AnimationDirection _direction;
   double _value;
 
   /// The animation whose value this animation will proxy.
@@ -112,7 +106,6 @@ class ProxyAnimation extends Animation<double>
       return;
     if (_parent != null) {
       _status = _parent.status;
-      _direction = _parent.direction;
       _value = _parent.value;
       if (isListening)
         didStopListening();
@@ -126,7 +119,6 @@ class ProxyAnimation extends Animation<double>
       if (_status != _parent.status)
         notifyStatusListeners(_parent.status);
       _status = null;
-      _direction = null;
       _value = null;
     }
   }
@@ -146,7 +138,6 @@ class ProxyAnimation extends Animation<double>
   }
 
   AnimationStatus get status => _parent != null ? _parent.status : _status;
-  AnimationDirection get direction => _parent != null ? _parent.direction : _direction;
   double get value => _parent != null ? _parent.value : _value;
 }
 
@@ -186,7 +177,6 @@ class ReverseAnimation extends Animation<double>
   }
 
   AnimationStatus get status => _reverseStatus(parent.status);
-  AnimationDirection get direction => _reverseDirection(parent.direction);
   double get value => 1.0 - parent.value;
 
   AnimationStatus _reverseStatus(AnimationStatus status) {
@@ -197,13 +187,6 @@ class ReverseAnimation extends Animation<double>
       case AnimationStatus.dismissed: return AnimationStatus.completed;
     }
   }
-
-  AnimationDirection _reverseDirection(AnimationDirection direction) {
-    switch (direction) {
-      case AnimationDirection.forward: return AnimationDirection.reverse;
-      case AnimationDirection.reverse: return AnimationDirection.forward;
-    }
-  }
 }
 
 /// An animation that applies a curve to another animation.
@@ -238,7 +221,7 @@ class CurvedAnimation extends Animation<double> with AnimationWithParentMixin<do
   /// The curve direction is only reset when we hit the beginning or the end of
   /// the timeline to avoid discontinuities in the value of any variables this
   /// a animation is used to animate.
-  AnimationDirection _curveDirection;
+  AnimationStatus _curveDirection;
 
   void _handleStatusChanged(AnimationStatus status) {
     switch (status) {
@@ -247,16 +230,16 @@ class CurvedAnimation extends Animation<double> with AnimationWithParentMixin<do
         _curveDirection = null;
         break;
       case AnimationStatus.forward:
-        _curveDirection ??= AnimationDirection.forward;
+        _curveDirection ??= AnimationStatus.forward;
         break;
       case AnimationStatus.reverse:
-        _curveDirection ??= AnimationDirection.reverse;
+        _curveDirection ??= AnimationStatus.reverse;
         break;
     }
   }
 
   double get value {
-    final bool useForwardCurve = reverseCurve == null || (_curveDirection ?? parent.direction) == AnimationDirection.forward;
+    final bool useForwardCurve = reverseCurve == null || (_curveDirection ?? parent.status) != AnimationStatus.reverse;
     Curve activeCurve = useForwardCurve ? curve : reverseCurve;
 
     double t = parent.value;
@@ -324,7 +307,6 @@ class TrainHoppingAnimation extends Animation<double>
   }
 
   AnimationStatus get status => _currentTrain.status;
-  AnimationDirection get direction => _currentTrain.direction;
 
   double _lastValue;
   void _valueChangeHandler() {

packages/flutter/lib/src/material/bottom_sheet.dart

@@ -51,7 +51,7 @@ class _BottomSheetState extends State<BottomSheet> {
     return renderBox.size.height;
   }
 
-  bool get _dismissUnderway => config.animationController.direction == AnimationDirection.reverse;
+  bool get _dismissUnderway => config.animationController.status == AnimationStatus.reverse;
 
   void _handleDragUpdate(double delta) {
     if (_dismissUnderway)

packages/flutter/lib/src/material/tabs.dart

@@ -809,7 +809,6 @@ class _TabBarViewState extends PageableListState<TabBarView> implements TabBarSe
 
   TabBarSelectionState _selection;
   List<Widget> _items;
-  AnimationDirection _scrollDirection = AnimationDirection.forward;
 
   int get _tabCount => config.children.length;
 
@@ -906,16 +905,11 @@ class _TabBarViewState extends PageableListState<TabBarView> implements TabBarSe
 
     if (selectedIndex < previousSelectedIndex) {
       _updateItemsFromChildren(selectedIndex, previousSelectedIndex);
-      _scrollDirection = AnimationDirection.reverse;
+      scrollTo(1.0 - animation.value);
     } else {
       _updateItemsFromChildren(previousSelectedIndex, selectedIndex);
-      _scrollDirection = AnimationDirection.forward;
-    }
-
-    if (_scrollDirection == AnimationDirection.forward)
       scrollTo(animation.value);
-    else
-      scrollTo(1.0 - animation.value);
+    }
   }
 
   void dispatchOnScroll() {

packages/flutter/lib/src/material/toggleable.dart

@@ -66,7 +66,10 @@ abstract class RenderToggleable extends RenderConstrainedBox implements Semantic
     _position
       ..curve = Curves.easeIn
       ..reverseCurve = Curves.easeOut;
-    _positionController.play(value ? AnimationDirection.forward : AnimationDirection.reverse);
+    if (value)
+      _positionController.forward();
+    else
+      _positionController.reverse();
   }
 
   Color get activeColor => _activeColor;

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

@@ -479,7 +479,8 @@ class HeroController extends NavigatorObserver {
 
   void _addHeroToOverlay(Widget hero, Object tag, OverlayState overlay) {
     OverlayEntry entry = new OverlayEntry(builder: (_) => hero);
-    if (_animation.direction == AnimationDirection.forward)
+    assert(_animation.status != AnimationStatus.dismissed && _animation.status != AnimationStatus.completed);
+    if (_animation.status == AnimationStatus.forward)
       _to.insertHeroOverlayEntry(entry, tag, overlay);
     else
       _from.insertHeroOverlayEntry(entry, tag, overlay);