Use AnimatedContainer for card_collection.dart.

sky/sdk/lib/widgets/animated_container.dart

 // 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 'package:vector_math/vector_math.dart';
 
 import '../animation/animation_performance.dart';
 import '../animation/curves.dart';
 import '../base/lerp.dart';
 import '../painting/box_painter.dart';
 import '../theme/shadows.dart';
 import 'basic.dart';
 
 // This class builds a Container object from a collection of optionally-
 // animated properties. Use syncFields to update the Container's properties,
 // which will optionally animate them using an AnimationPerformance.
 class AnimatedContainer {
+  AnimatedType<double> opacity;
   AnimatedType<Point> position;
   AnimatedType<double> shadow;
   AnimatedColor backgroundColor;
 
   // These don't animate, but are used to build the Container anyway.
   double borderRadius;
   Shape shape;
 
   Map<AnimatedVariable, AnimationPerformance> _variableToPerformance =
       new Map<AnimatedVariable, AnimationPerformance>();
 
   AnimatedContainer();
 
-  AnimationPerformance createPerformance(AnimatedType variable,
+  AnimationPerformance createPerformance(List<AnimatedType> variables,
                                          {Duration duration}) {
     AnimationPerformance performance = new AnimationPerformance()
       ..duration = duration
-      ..variable = variable;
-    _variableToPerformance[variable] = performance;
+      ..variable = new AnimatedList(variables);
+    for (AnimatedVariable variable in variables)
+      _variableToPerformance[variable] = performance;
     return performance;
   }
 
   Widget build(Widget child) {
     Widget current = child;
     if (shadow != null || backgroundColor != null ||
         borderRadius != null || shape != null) {
       current = new DecoratedBox(
         decoration: new BoxDecoration(
           borderRadius: borderRadius,
           shape: shape,
           boxShadow: shadow != null ? _computeShadow(shadow.value) : null,
           backgroundColor: backgroundColor != null ? backgroundColor.value : null),
         child: current);
     }
 
     if (position != null) {
       Matrix4 transform = new Matrix4.identity();
       transform.translate(position.value.x, position.value.y);
-      current = new Transform(transform: transform, child: child);
+      current = new Transform(transform: transform, child: current);
+    }
+
+    if (opacity != null) {
+      current = new Opacity(opacity: opacity.value, child: current);
     }
 
     return current;
   }
 
   void syncFields(AnimatedContainer source) {
     _syncField(position, source.position);
     _syncField(shadow, source.shadow);
     _syncField(backgroundColor, source.backgroundColor);
 
@@ skipping 39 matching lines @@
 
   int level1 = level.floor();
   int level2 = level.ceil();
   double t = level - level1.toDouble();
 
   List<BoxShadow> shadow = new List<BoxShadow>();
   for (int i = 0; i < shadows[level1].length; ++i)
     shadow.add(lerpBoxShadow(shadows[level1][i], shadows[level2][i], t));
   return shadow;
 }