add initState, rename animated_container

sky/sdk/lib/widgets/widget.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 'dart:async';
 import 'dart:collection';
 import 'dart:sky' as sky;
 
 import 'package:sky/mojo/activity.dart' as activity;
 
@@ skipping 503 matching lines @@
 
   Widget build();
 
 }
 
 abstract class StatefulComponent extends Component {
 
   StatefulComponent({ String key }) : super(key: key);
 
   bool _disqualifiedFromEverAppearingAgain = false;
+  bool _isStateInitialized = false;
 
   void didMount() {
     assert(!_disqualifiedFromEverAppearingAgain);
     super.didMount();
   }
 
   void _buildIfDirty() {
     assert(!_disqualifiedFromEverAppearingAgain);
     super._buildIfDirty();
   }
 
   void _sync(Widget old, dynamic slot) {
     assert(!_disqualifiedFromEverAppearingAgain);
+    // TODO(ianh): _sync should only be called once when old == null
+    if (old == null && !_isStateInitialized) {
+      initState();
+      _isStateInitialized = true;
+    }
     super._sync(old, slot);
   }
 
   Widget syncChild(Widget node, Widget oldNode, dynamic slot) {
     assert(!_disqualifiedFromEverAppearingAgain);
     return super.syncChild(node, oldNode, slot);
   }
 
   bool retainStatefulNodeIfPossible(StatefulComponent newNode) {
     assert(!_disqualifiedFromEverAppearingAgain);
@@ skipping 13 matching lines @@
   }
 
   // This is called by retainStatefulNodeIfPossible(), during
   // syncChild(), just before _sync() is called. Derived
   // classes should override this method to update `this` to
   // account for the new values the parent passed to `source`.
   // Make sure to call super.syncFields(source) unless you are
   // extending StatefulComponent directly.
   void syncFields(Component source);
 
+  // Stateful components can override initState if they want
+  // to do non-trivial work to initialize state. This is
+  // always called before build().
+  void initState() { }
+
   void setState(Function fn()) {
     assert(!_disqualifiedFromEverAppearingAgain);
     fn();
     scheduleBuild();
   }
 }
 
 Set<Component> _dirtyComponents = new Set<Component>();
 bool _buildScheduled = false;
 bool _inRenderDirtyComponents = false;
@@ skipping 550 matching lines @@
     if (root.parent == null) {
       // we haven't attached it yet
       assert(_container.child == null);
       _container.child = root;
     }
     assert(root.parent == _container);
   }
 
   Widget build() => builder();
 }