Refactor stateful parts of Component into StatefulComponent

R=abarth@chromium.org, abarth@google.com

Review URL: https://codereview.chromium.org/1217093005.

sdk/example/mine_digger/lib/main.dart

@@ -185,7 +185,7 @@ class Game {
 
   void handleBannerPointerDown(sky.PointerEvent event) {
     initialize();
-    app.setState((){});
+    app.scheduleBuild();
   }
 
   // User action. The user uncovers the cell which can cause losing the game.
@@ -203,7 +203,7 @@ class Game {
       // No mine, uncover nearby if possible.
       cull(x, y);
     }
-    app.setState((){});
+    app.scheduleBuild();
   }
 
   // User action. The user is sure a mine is at this location.
@@ -215,7 +215,7 @@ class Game {
       uiState[y][x] = flaggedCell;
       ++detectedCount;
     }
-    app.setState((){});
+    app.scheduleBuild();
   }
 
   // Recursively uncovers cells whose totalMineCount is zero.

sdk/example/stocks/lib/stock_home.dart

@@ -29,9 +29,9 @@ import 'stock_types.dart';
 
 typedef void ModeUpdater(StockMode mode);
 
-class StockHome extends Component {
+class StockHome extends StatefulComponent {
 
-  StockHome(this.navigator, this.stocks, this.stockMode, this.modeUpdater) : super(stateful: true) {
+  StockHome(this.navigator, this.stocks, this.stockMode, this.modeUpdater) {
     // if (debug)
     //   new Timer(new Duration(seconds: 1), dumpState);
     _drawerController = new DrawerController(_handleDrawerStatusChanged);

sdk/example/stocks/lib/stock_settings.dart

@@ -21,9 +21,9 @@ typedef void SettingsUpdater({
   BackupMode backup
 });
 
-class StockSettings extends Component {
+class StockSettings extends StatefulComponent {
 
-  StockSettings(this.navigator, this.optimism, this.backup, this.updater) : super(stateful: true);
+  StockSettings(this.navigator, this.optimism, this.backup, this.updater);
 
   Navigator navigator;
   StockMode optimism;

sdk/lib/editing/editable_text.dart

@@ -15,14 +15,14 @@ const _kCursorGap = 1.0;
 const _kCursorHeightOffset = 2.0;
 const _kCursorWidth = 1.0;
 
-class EditableText extends Component {
+class EditableText extends StatefulComponent {
 
   EditableText({
     String key,
     this.value,
     this.focused: false,
     this.style,
-    this.cursorColor}) : super(key: key, stateful: true);
+    this.cursorColor}) : super(key: key);
 
   EditableString value;
   bool focused;

sdk/lib/editing/input.dart

@@ -14,13 +14,13 @@ typedef void ValueChanged(value);
 const double _kHintOpacity = 0.26;
 const EdgeDims _kTextfieldPadding = const EdgeDims.symmetric(vertical: 8.0);
 
-class Input extends Component {
+class Input extends StatefulComponent {
 
   Input({String key,
          this.placeholder,
          this.onChanged,
          this.focused})
-      : super(key: key, stateful: true) {
+      : super(key: key) {
     _editableValue = new EditableString(
       text: _value,
       onUpdated: _handleTextUpdated

sdk/lib/widgets/README.md

@@ -254,8 +254,8 @@ class MyCheckbox extends Component {
   }
 }
 
-class MyDialog extends Component {
-  MyDialog({ this.onDismissed }) : super(stateful: true);
+class MyDialog extends StatefulComponent {
+  MyDialog({ this.onDismissed });
 
   Function onDismissed;
   bool _checkboxValue = false;
@@ -298,8 +298,7 @@ component persists for the lifetime of the application.
 The `MyDialog` component is more complicated because it is a stateful component.
 Let's walk through the differences in `MyDialog` caused by its being stateful:
 
- * `MyDialog` passes `stateful: true` to the `Component` constructor, marking
-   the component stateful.
+ * `MyDialog` extends StatefulComponent instead of Component.
 
  * `MyDialog` has non-`final` member variables. Over the lifetime of the dialog,
    we'll need to modify the values of these member variables, which means we

sdk/lib/widgets/animated_component.dart

@@ -17,9 +17,9 @@ class _AnimationEntry {
   StreamSubscription<double> subscription;
 }
 
-abstract class AnimatedComponent extends Component {
+abstract class AnimatedComponent extends StatefulComponent {
 
-  AnimatedComponent({ String key }) : super(key: key, stateful: true);
+  AnimatedComponent({ String key }) : super(key: key);
 
   void syncFields(AnimatedComponent source) { }
 

sdk/lib/widgets/basic.dart

@@ -22,7 +22,7 @@ import 'widget.dart';
 export '../rendering/box.dart' show BackgroundImage, BoxConstraints, BoxDecoration, Border, BorderSide, EdgeDims;
 export '../rendering/flex.dart' show FlexDirection, FlexJustifyContent, FlexAlignItems;
 export '../rendering/object.dart' show Point, Offset, Size, Rect, Color, Paint, Path;
-export 'widget.dart' show Widget, Component, App, runApp, Listener, ParentDataNode;
+export 'widget.dart' show Widget, Component, StatefulComponent, App, runApp, Listener, ParentDataNode;
 
 
 // PAINTING NODES
@@ -505,8 +505,8 @@ class Image extends LeafRenderObjectWrapper {
   }
 }
 
-class FutureImage extends Component {
-  FutureImage({ this.image, this.size }) : super(stateful: true);
+class FutureImage extends StatefulComponent {
+  FutureImage({ this.image, this.size });
 
   Future<sky.Image> image;
   Size size;

sdk/lib/widgets/button_base.dart

@@ -4,9 +4,9 @@
 
 import 'basic.dart';
 
-abstract class ButtonBase extends Component {
+abstract class ButtonBase extends StatefulComponent {
 
-  ButtonBase({ String key, this.highlight: false }) : super(key: key, stateful: true);
+  ButtonBase({ String key, this.highlight: false }) : super(key: key);
 
   bool highlight;
 

sdk/lib/widgets/navigator.dart

@@ -74,9 +74,9 @@ class NavigationState {
   }
 }
 
-class Navigator extends Component {
+class Navigator extends StatefulComponent {
 
-  Navigator(this.state, { String key }) : super(key: key, stateful: true);
+  Navigator(this.state, { String key }) : super(key: key);
 
   NavigationState state;
 

sdk/lib/widgets/scrollable.dart

@@ -24,13 +24,13 @@ abstract class ScrollClient {
 
 enum ScrollDirection { vertical, horizontal }
 
-abstract class Scrollable extends Component {
+abstract class Scrollable extends StatefulComponent {
 
   Scrollable({
    String key,
    this.backgroundColor,
    this.direction: ScrollDirection.vertical
-  }) : super(key: key, stateful: true);
+  }) : super(key: key);
 
   Color backgroundColor;
   ScrollDirection direction;

sdk/lib/widgets/widget.dart

@@ -137,9 +137,6 @@ abstract class Widget {
   // Returns the child which should be retained as the child of this node.
   Widget syncChild(Widget newNode, Widget oldNode, dynamic slot) {
 
-    assert(oldNode is! Component ||
-           (oldNode is Component && !oldNode._disqualifiedFromEverAppearingAgain)); // TODO(ianh): Simplify this once the analyzer is cleverer
-
     if (newNode == oldNode) {
       assert(newNode == null || newNode.mounted);
       assert(newNode is! RenderObjectWrapper ||
@@ -359,26 +356,18 @@ class Listener extends TagNode  {
 
 abstract class Component extends Widget {
 
-  Component({ String key, bool stateful })
-      : _stateful = stateful != null ? stateful : false,
-        _order = _currentOrder + 1,
+  Component({ String key })
+      : _order = _currentOrder + 1,
         super._withKey(key);
 
   static Component _currentlyBuilding;
   bool get _isBuilding => _currentlyBuilding == this;
 
-  bool _stateful;
   bool _dirty = true;
-  bool _disqualifiedFromEverAppearingAgain = false;
 
   Widget _built;
   dynamic _slot; // cached slot from the last time we were synced
 
-  void didMount() {
-    assert(!_disqualifiedFromEverAppearingAgain);
-    super.didMount();
-  }
-
   void remove() {
     assert(_built != null);
     assert(root != null);
@@ -408,38 +397,6 @@ abstract class Component extends Widget {
     scheduleBuild();
   }
 
-  bool _retainStatefulNodeIfPossible(Component old) {
-    assert(!_disqualifiedFromEverAppearingAgain);
-
-    if (old == null || !old._stateful)
-      return false;
-
-    assert(runtimeType == old.runtimeType);
-    assert(key == old.key);
-
-    // Make |this|, the newly-created object, into the "old" Component, and kill it
-    _stateful = false;
-    _built = old._built;
-    assert(_built != null);
-    _disqualifiedFromEverAppearingAgain = true;
-
-    // Make |old| the "new" component
-    old._built = null;
-    old._dirty = true;
-    old.syncFields(this);
-    return true;
-  }
-
-  // This is called by _retainStatefulNodeIfPossible(), during
-  // syncChild(), just before _sync() is called.
-  // This must be implemented on any subclass that can become stateful
-  // (but don't call super.syncFields() if you inherit directly from
-  // Component, since that'll fire an assert).
-  // If you don't ever become stateful, then don't override this.
-  void syncFields(Component source) {
-    assert(false);
-  }
-
   // order corresponds to _build_ order, not depth in the tree.
   // All the Components built by a particular other Component will have the
   // same order, regardless of whether one is subsequently inserted
@@ -457,7 +414,6 @@ abstract class Component extends Widget {
   //      assert(_built == null && old != null)
   void _sync(Component old, dynamic slot) {
     assert(_built == null || old == null);
-    assert(!_disqualifiedFromEverAppearingAgain);
 
     _slot = slot;
 
@@ -487,7 +443,6 @@ abstract class Component extends Widget {
   }
 
   void _buildIfDirty() {
-    assert(!_disqualifiedFromEverAppearingAgain);
     if (!_dirty || !_mounted)
       return;
 
@@ -496,21 +451,76 @@ abstract class Component extends Widget {
   }
 
   void scheduleBuild() {
-    assert(!_disqualifiedFromEverAppearingAgain);
     if (_isBuilding || _dirty || !_mounted)
       return;
     _dirty = true;
     _scheduleComponentForRender(this);
   }
 
+  Widget build();
+
+}
+
+abstract class StatefulComponent extends Component {
+
+  StatefulComponent({ String key }) : super(key: key);
+
+  bool _disqualifiedFromEverAppearingAgain = false;
+
+  void didMount() {
+    assert(!_disqualifiedFromEverAppearingAgain);
+    super.didMount();
+  }
+
+  void _buildIfDirty() {
+    assert(!_disqualifiedFromEverAppearingAgain);
+    super._buildIfDirty();
+  }
+
+  void _sync(Widget old, dynamic slot) {
+    assert(!_disqualifiedFromEverAppearingAgain);
+    super._sync(old, slot);
+  }
+
+  Widget syncChild(Widget node, Widget oldNode, dynamic slot) {
+    assert(!_disqualifiedFromEverAppearingAgain);
+    return super.syncChild(node, oldNode, slot);
+  }
+
+  bool _retainStatefulNodeIfPossible(StatefulComponent old) {
+    assert(!_disqualifiedFromEverAppearingAgain);
+
+    if (old == null)
+      return false;
+
+    assert(runtimeType == old.runtimeType);
+    assert(key == old.key);
+
+    // Make |this|, the newly-created object, into the "old" Component, and kill it
+    _built = old._built;
+    assert(_built != null);
+    _disqualifiedFromEverAppearingAgain = true;
+
+    // Make |old| the "new" component
+    old._built = null;
+    old._dirty = true;
+    old.syncFields(this);
+    return true;
+  }
+
+  // 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);
+
   void setState(Function fn()) {
-    assert(_stateful);
+    assert(!_disqualifiedFromEverAppearingAgain);
     fn();
     scheduleBuild();
   }
-
-  Widget build();
-
 }
 
 Set<Component> _dirtyComponents = new Set<Component>();
@@ -930,10 +940,9 @@ class WidgetSkyBinding extends SkyBinding {
 
 }
 
-abstract class App extends Component {
+abstract class App extends StatefulComponent {
 
-  // Apps are assumed to be stateful
-  App({ String key }) : super(key: key, stateful: true);
+  App({ String key }) : super(key: key);
 
   void _handleEvent(sky.Event event) {
     if (event.type == 'back')
@@ -950,13 +959,15 @@ abstract class App extends Component {
     SkyBinding.instance.removeEventListener(_handleEvent);
   }
 
+  void syncFields(Component source) { }
+
   // Override this to handle back button behavior in your app
   void onBack() { }
 }
 
-abstract class AbstractWidgetRoot extends Component {
+abstract class AbstractWidgetRoot extends StatefulComponent {
 
-  AbstractWidgetRoot() : super(stateful: true) {
+  AbstractWidgetRoot() {
     _mounted = true;
     _scheduleComponentForRender(this);
   }