Refactor fn2.dart, since it breached our 1000-line threshold.

sky/sdk/lib/framework/widgets/ui_node.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.
 
-library fn;
-
-import 'app.dart';
 import 'dart:async';
 import 'dart:collection';
 import 'dart:mirrors';
 import 'dart:sky' as sky;
-import 'package:vector_math/vector_math.dart';
-import 'rendering/block.dart';
-import 'rendering/box.dart';
-import 'rendering/flex.dart';
-import 'rendering/object.dart';
-import 'rendering/paragraph.dart';
-import 'rendering/stack.dart';
-export 'rendering/object.dart' show Point, Size, Rect, Color, Paint, Path;
-export 'rendering/box.dart' show BoxConstraints, BoxDecoration, Border, BorderSide, EdgeDims;
-export 'rendering/flex.dart' show FlexDirection;
+
+import '../app.dart';
+import '../rendering/box.dart';
+import '../rendering/object.dart';
+
+export '../rendering/box.dart' show BoxConstraints, BoxDecoration, Border, BorderSide, EdgeDims;
+export '../rendering/flex.dart' show FlexDirection;
+export '../rendering/object.dart' show Point, Size, Rect, Color, Paint, Path;
+
 
 // final sky.Tracing _tracing = sky.window.tracing;
 
 final bool _shouldLogRenderDuration = false;
 
 /*
  * All Effen nodes derive from UINode. All nodes have a _parent, a _key and
  * can be sync'd.
  */
 abstract class UINode {
@@ skipping 116 matching lines @@
     }
 
     assert(!node.mounted);
     node.setParent(this);
     node._sync(oldNode, slot);
     assert(node.root is RenderObject);
     return node;
   }
 }
 
+
 // Descendants of TagNode provide a way to tag RenderObjectWrapper and
 // Component nodes with annotations, such as event listeners,
 // stylistic information, etc.
 abstract class TagNode extends UINode {
 
   TagNode(UINode content, { Object key }) : this.content = content, super(key: key);
 
   UINode content;
 
   void _sync(UINode old, dynamic slot) {
@@ skipping 100 matching lines @@
 
   void _handleEvent(sky.Event e) {
     sky.EventListener listener = listeners[e.type];
     if (listener != null) {
       listener(e);
     }
   }
 
 }
 
+
+abstract class Component extends UINode {
+
+  Component({ Object key, bool stateful })
+      : _stateful = stateful != null ? stateful : false,
+        _order = _currentOrder + 1,
+        super(key: key);
+
+  Component.fromArgs(Object key, bool stateful)
+      : this(key: key, stateful: stateful);
+
+  static Component _currentlyBuilding;
+  bool get _isBuilding => _currentlyBuilding == this;
+
+  bool _stateful;
+  bool _dirty = true;
+  bool _disqualifiedFromEverAppearingAgain = false;
+
+  UINode _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);
+    removeChild(_built);
+    _built = null;
+    super.remove();
+  }
+
+  bool _retainStatefulNodeIfPossible(UINode old) {
+    assert(!_disqualifiedFromEverAppearingAgain);
+
+    Component oldComponent = old as Component;
+    if (oldComponent == null || !oldComponent._stateful)
+      return false;
+
+    assert(key == oldComponent.key);
+
+    // Make |this|, the newly-created object, into the "old" Component, and kill it
+    _stateful = false;
+    _built = oldComponent._built;
+    assert(_built != null);
+    _disqualifiedFromEverAppearingAgain = true;
+
+    // Make |oldComponent| the "new" component
+    oldComponent._built = null;
+    oldComponent._dirty = true;
+    oldComponent.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);
+  }
+
+  final int _order;
+  static int _currentOrder = 0;
+
+  /* There are three cases here:
+   * 1) Building for the first time:
+   *      assert(_built == null && old == null)
+   * 2) Re-building (because a dirty flag got set):
+   *      assert(_built != null && old == null)
+   * 3) Syncing against an old version
+   *      assert(_built == null && old != null)
+   */
+  void _sync(UINode old, dynamic slot) {
+    assert(_built == null || old == null);
+    assert(!_disqualifiedFromEverAppearingAgain);
+
+    Component oldComponent = old as Component;
+
+    _slot = slot;
+
+    var oldBuilt;
+    if (oldComponent == null) {
+      oldBuilt = _built;
+    } else {
+      assert(_built == null);
+      oldBuilt = oldComponent._built;
+    }
+
+    int lastOrder = _currentOrder;
+    _currentOrder = _order;
+    _currentlyBuilding = this;
+    _built = build();
+    assert(_built != null);
+    _currentlyBuilding = null;
+    _currentOrder = lastOrder;
+
+    _built = syncChild(_built, oldBuilt, slot);
+    assert(_built != null);
+    _dirty = false;
+    _root = _built.root;
+    assert(_root == root); // in case a subclass reintroduces it
+    assert(root != null);
+  }
+
+  void _buildIfDirty() {
+    assert(!_disqualifiedFromEverAppearingAgain);
+    if (!_dirty || !_mounted)
+      return;
+
+    assert(root != null);
+    _sync(null, _slot);
+  }
+
+  void scheduleBuild() {
+    setState(() {});
+  }
+
+  void setState(Function fn()) {
+    assert(!_disqualifiedFromEverAppearingAgain);
+    _stateful = true;
+    fn();
+    if (_isBuilding || _dirty || !_mounted)
+      return;
+
+    _dirty = true;
+    _scheduleComponentForRender(this);
+  }
+
+  UINode build();
+
+}
+
+Set<Component> _dirtyComponents = new Set<Component>();
+bool _buildScheduled = false;
+bool _inRenderDirtyComponents = false;
+
+void _buildDirtyComponents() {
+  //_tracing.begin('fn::_buildDirtyComponents');
+
+  Stopwatch sw;
+  if (_shouldLogRenderDuration)
+    sw = new Stopwatch()..start();
+
+  try {
+    _inRenderDirtyComponents = true;
+
+    List<Component> sortedDirtyComponents = _dirtyComponents.toList();
+    sortedDirtyComponents.sort((Component a, Component b) => a._order - b._order);
+    for (var comp in sortedDirtyComponents) {
+      comp._buildIfDirty();
+    }
+
+    _dirtyComponents.clear();
+    _buildScheduled = false;
+  } finally {
+    _inRenderDirtyComponents = false;
+  }
+
+  UINode._notifyMountStatusChanged();
+
+  if (_shouldLogRenderDuration) {
+    sw.stop();
+    print('Render took ${sw.elapsedMicroseconds} microseconds');
+  }
+
+  //_tracing.end('fn::_buildDirtyComponents');
+}
+
+void _scheduleComponentForRender(Component c) {
+  assert(!_inRenderDirtyComponents);
+  _dirtyComponents.add(c);
+
+  if (!_buildScheduled) {
+    _buildScheduled = true;
+    new Future.microtask(_buildDirtyComponents);
+  }
+}
+
+
 /*
  * RenderObjectWrappers correspond to a desired state of a RenderObject.
  * They are fully immutable, with one exception: A UINode which is a
  * Component which lives within an MultiChildRenderObjectWrapper's
  * children list, may be replaced with the "old" instance if it has
  * become stateful.
  */
 abstract class RenderObjectWrapper extends UINode {
 
   RenderObjectWrapper({
@@ skipping 83 matching lines @@
   }
 
   void remove() {
     if (child != null)
       removeChild(child);
     super.remove();
   }
 
 }
 
-class Opacity extends OneChildRenderObjectWrapper {
-  Opacity({ this.opacity, UINode child, Object key })
-    : super(child: child, key: key);
-
-  RenderOpacity get root { RenderOpacity result = super.root; return result; }
-  final double opacity;
-
-  RenderOpacity createNode() => new RenderOpacity(opacity: opacity);
-
-  void syncRenderObject(Opacity old) {
-    super.syncRenderObject(old);
-    root.opacity = opacity;
-  }
-}
-
-class ClipRect extends OneChildRenderObjectWrapper {
-
-  ClipRect({ UINode child, Object key })
-    : super(child: child, key: key);
-
-  RenderClipRect get root { RenderClipRect result = super.root; return result; }
-  RenderClipRect createNode() => new RenderClipRect();
-}
-
-class ClipOval extends OneChildRenderObjectWrapper {
-
-  ClipOval({ UINode child, Object key })
-    : super(child: child, key: key);
-
-  RenderClipOval get root { RenderClipOval result = super.root; return result; }
-  RenderClipOval createNode() => new RenderClipOval();
-}
-
-class Padding extends OneChildRenderObjectWrapper {
-
-  Padding({ this.padding, UINode child, Object key })
-    : super(child: child, key: key);
-
-  RenderPadding get root { RenderPadding result = super.root; return result; }
-  final EdgeDims padding;
-
-  RenderPadding createNode() => new RenderPadding(padding: padding);
-
-  void syncRenderObject(Padding old) {
-    super.syncRenderObject(old);
-    root.padding = padding;
-  }
-
-}
-
-class DecoratedBox extends OneChildRenderObjectWrapper {
-
-  DecoratedBox({ this.decoration, UINode child, Object key })
-    : super(child: child, key: key);
-
-  RenderDecoratedBox get root { RenderDecoratedBox result = super.root; return result; }
-  final BoxDecoration decoration;
-
-  RenderDecoratedBox createNode() => new RenderDecoratedBox(decoration: decoration);
-
-  void syncRenderObject(DecoratedBox old) {
-    super.syncRenderObject(old);
-    root.decoration = decoration;
-  }
-
-}
-
-class SizedBox extends OneChildRenderObjectWrapper {
-
-  SizedBox({
-    double width: double.INFINITY,
-    double height: double.INFINITY,
-    UINode child,
-    Object key
-  }) : desiredSize = new Size(width, height), super(child: child, key: key);
-
-  RenderSizedBox get root { RenderSizedBox result = super.root; return result; }
-  final Size desiredSize;
-
-  RenderSizedBox createNode() => new RenderSizedBox(desiredSize: desiredSize);
-
-  void syncRenderObject(SizedBox old) {
-    super.syncRenderObject(old);
-    root.desiredSize = desiredSize;
-  }
-
-}
-
-class ConstrainedBox extends OneChildRenderObjectWrapper {
-
-  ConstrainedBox({ this.constraints, UINode child, Object key })
-    : super(child: child, key: key);
-
-  RenderConstrainedBox get root { RenderConstrainedBox result = super.root; return result; }
-  final BoxConstraints constraints;
-
-  RenderConstrainedBox createNode() => new RenderConstrainedBox(additionalConstraints: constraints);
-
-  void syncRenderObject(ConstrainedBox old) {
-    super.syncRenderObject(old);
-    root.additionalConstraints = constraints;
-  }
-
-}
-
-class ShrinkWrapWidth extends OneChildRenderObjectWrapper {
-
-  ShrinkWrapWidth({ UINode child, Object key }) : super(child: child, key: key);
-
-  RenderShrinkWrapWidth get root { RenderShrinkWrapWidth result = super.root; return result; }
-
-  RenderShrinkWrapWidth createNode() => new RenderShrinkWrapWidth();
-
-}
-
-class Transform extends OneChildRenderObjectWrapper {
-
-  Transform({ this.transform, UINode child, Object key })
-    : super(child: child, key: key);
-
-  RenderTransform get root { RenderTransform result = super.root; return result; }
-  final Matrix4 transform;
-
-  RenderTransform createNode() => new RenderTransform(transform: transform);
-
-  void syncRenderObject(Transform old) {
-    super.syncRenderObject(old);
-    root.transform = transform;
-  }
-
-}
-
-class SizeObserver extends OneChildRenderObjectWrapper {
-
-  SizeObserver({ this.callback, UINode child, Object key })
-    : super(child: child, key: key);
-
-  RenderSizeObserver get root { RenderSizeObserver result = super.root; return result; }
-  final SizeChangedCallback callback;
-
-  RenderSizeObserver createNode() => new RenderSizeObserver(callback: callback);
-
-  void syncRenderObject(SizeObserver old) {
-    super.syncRenderObject(old);
-    root.callback = callback;
-  }
-
-  void remove() {
-    root.callback = null;
-    super.remove();
-  }
-
-}
-
-// TODO(jackson) need a mechanism for marking the RenderCustomPaint as needing paint
-class CustomPaint extends OneChildRenderObjectWrapper {
-
-  CustomPaint({ this.callback, UINode child, Object key })
-    : super(child: child, key: key);
-
-  RenderCustomPaint get root { RenderCustomPaint result = super.root; return result; }
-  final CustomPaintCallback callback;
-
-  RenderCustomPaint createNode() => new RenderCustomPaint(callback: callback);
-
-  void syncRenderObject(CustomPaint old) {
-    super.syncRenderObject(old);
-    root.callback = callback;
-  }
-
-  void remove() {
-    root.callback = null;
-    super.remove();
-  }
-
-}
-
 abstract class MultiChildRenderObjectWrapper extends RenderObjectWrapper {
 
   // In MultiChildRenderObjectWrapper subclasses, slots are RenderObject nodes
   // to use as the "insert before" sibling in ContainerRenderObjectMixin.add() calls
 
   MultiChildRenderObjectWrapper({
     Object key,
     List<UINode> children
   }) : this.children = children == null ? const [] : children,
        super(key: key) {
@@ skipping 165 matching lines @@
       oldNode = oldChildren[oldStartIndex];
       removeChild(oldNode);
       advanceOldStartIndex();
     }
 
     assert(root == this.root); // TODO(ianh): Remove this once the analyzer is cleverer
   }
 
 }
 
-class Block extends MultiChildRenderObjectWrapper {
-
-  Block(List<UINode> children, { Object key })
-    : super(key: key, children: children);
-
-  RenderBlock get root { RenderBlock result = super.root; return result; }
-  RenderBlock createNode() => new RenderBlock();
-
-}
-
-class Stack extends MultiChildRenderObjectWrapper {
-
-  Stack(List<UINode> children, { Object key })
-    : super(key: key, children: children);
-
-  RenderStack get root { RenderStack result = super.root; return result; }
-  RenderStack createNode() => new RenderStack();
-
-}
-
-class StackPositionedChild extends ParentDataNode {
-  StackPositionedChild(UINode content, {
-    double top, double right, double bottom, double left
-  }) : super(content, new StackParentData()..top = top
-                                           ..right = right
-                                           ..bottom = bottom
-                                           ..left = left);
-}
-
-class Paragraph extends RenderObjectWrapper {
-
-  Paragraph({ Object key, this.text }) : super(key: key);
-
-  RenderParagraph get root { RenderParagraph result = super.root; return result; }
-  RenderParagraph createNode() => new RenderParagraph(text: text);
-
-  final String text;
-
-  void syncRenderObject(UINode old) {
-    super.syncRenderObject(old);
-    root.text = text;
-  }
-
-  void insert(RenderObjectWrapper child, dynamic slot) {
-    assert(false);
-    // Paragraph does not support having children currently
-  }
-
-}
-
-class Text extends Component {
-  Text(this.data) : super(key: '*text*');
-  final String data;
-  bool get interchangeable => true;
-  UINode build() => new Paragraph(text: data);
-}
-
-class Flex extends MultiChildRenderObjectWrapper {
-
-  Flex(List<UINode> children, {
-    Object key,
-    this.direction: FlexDirection.horizontal,
-    this.justifyContent: FlexJustifyContent.flexStart,
-    this.alignItems: FlexAlignItems.center
-  }) : super(key: key, children: children);
-
-  RenderFlex get root { RenderFlex result = super.root; return result; }
-  RenderFlex createNode() => new RenderFlex(direction: this.direction);
-
-  final FlexDirection direction;
-  final FlexJustifyContent justifyContent;
-  final FlexAlignItems alignItems;
-
-  void syncRenderObject(UINode old) {
-    super.syncRenderObject(old);
-    root.direction = direction;
-    root.justifyContent = justifyContent;
-    root.alignItems = alignItems;
-  }
-
-}
-
-class FlexExpandingChild extends ParentDataNode {
-  FlexExpandingChild(UINode content, { int flex: 1, Object key })
-    : super(content, new FlexBoxParentData()..flex = flex, key: key);
-}
-
-class Image extends RenderObjectWrapper {
-
-  Image({
-    Object key,
-    this.src,
-    this.size
-  }) : super(key: key);
-
-  RenderImage get root { RenderImage result = super.root; return result; }
-  RenderImage createNode() => new RenderImage(this.src, this.size);
-
-  final String src;
-  final Size size;
-
-  void syncRenderObject(UINode old) {
-    super.syncRenderObject(old);
-    root.src = src;
-    root.requestedSize = size;
-  }
-
-  void insert(RenderObjectWrapper child, dynamic slot) {
-    assert(false);
-    // Image does not support having children currently
-  }
-
-}
-
-Set<Component> _dirtyComponents = new Set<Component>();
-bool _buildScheduled = false;
-bool _inRenderDirtyComponents = false;
-
-void _buildDirtyComponents() {
-  //_tracing.begin('fn::_buildDirtyComponents');
-
-  Stopwatch sw;
-  if (_shouldLogRenderDuration)
-    sw = new Stopwatch()..start();
-
-  try {
-    _inRenderDirtyComponents = true;
-
-    List<Component> sortedDirtyComponents = _dirtyComponents.toList();
-    sortedDirtyComponents.sort((Component a, Component b) => a._order - b._order);
-    for (var comp in sortedDirtyComponents) {
-      comp._buildIfDirty();
-    }
-
-    _dirtyComponents.clear();
-    _buildScheduled = false;
-  } finally {
-    _inRenderDirtyComponents = false;
-  }
-
-  UINode._notifyMountStatusChanged();
-
-  if (_shouldLogRenderDuration) {
-    sw.stop();
-    print('Render took ${sw.elapsedMicroseconds} microseconds');
-  }
-
-  //_tracing.end('fn::_buildDirtyComponents');
-}
-
-void _scheduleComponentForRender(Component c) {
-  assert(!_inRenderDirtyComponents);
-  _dirtyComponents.add(c);
-
-  if (!_buildScheduled) {
-    _buildScheduled = true;
-    new Future.microtask(_buildDirtyComponents);
-  }
-}
-
-abstract class Component extends UINode {
-
-  Component({ Object key, bool stateful })
-      : _stateful = stateful != null ? stateful : false,
-        _order = _currentOrder + 1,
-        super(key: key);
-
-  Component.fromArgs(Object key, bool stateful)
-      : this(key: key, stateful: stateful);
-
-  static Component _currentlyBuilding;
-  bool get _isBuilding => _currentlyBuilding == this;
-
-  bool _stateful;
-  bool _dirty = true;
-  bool _disqualifiedFromEverAppearingAgain = false;
-
-  UINode _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);
-    removeChild(_built);
-    _built = null;
-    super.remove();
-  }
-
-  bool _retainStatefulNodeIfPossible(UINode old) {
-    assert(!_disqualifiedFromEverAppearingAgain);
-
-    Component oldComponent = old as Component;
-    if (oldComponent == null || !oldComponent._stateful)
-      return false;
-
-    assert(key == oldComponent.key);
-
-    // Make |this|, the newly-created object, into the "old" Component, and kill it
-    _stateful = false;
-    _built = oldComponent._built;
-    assert(_built != null);
-    _disqualifiedFromEverAppearingAgain = true;
-
-    // Make |oldComponent| the "new" component
-    oldComponent._built = null;
-    oldComponent._dirty = true;
-    oldComponent.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);
-  }
-
-  final int _order;
-  static int _currentOrder = 0;
-
-  /* There are three cases here:
-   * 1) Building for the first time:
-   *      assert(_built == null && old == null)
-   * 2) Re-building (because a dirty flag got set):
-   *      assert(_built != null && old == null)
-   * 3) Syncing against an old version
-   *      assert(_built == null && old != null)
-   */
-  void _sync(UINode old, dynamic slot) {
-    assert(_built == null || old == null);
-    assert(!_disqualifiedFromEverAppearingAgain);
-
-    Component oldComponent = old as Component;
-
-    _slot = slot;
-
-    var oldBuilt;
-    if (oldComponent == null) {
-      oldBuilt = _built;
-    } else {
-      assert(_built == null);
-      oldBuilt = oldComponent._built;
-    }
-
-    int lastOrder = _currentOrder;
-    _currentOrder = _order;
-    _currentlyBuilding = this;
-    _built = build();
-    assert(_built != null);
-    _currentlyBuilding = null;
-    _currentOrder = lastOrder;
-
-    _built = syncChild(_built, oldBuilt, slot);
-    assert(_built != null);
-    _dirty = false;
-    _root = _built.root;
-    assert(_root == root); // in case a subclass reintroduces it
-    assert(root != null);
-  }
-
-  void _buildIfDirty() {
-    assert(!_disqualifiedFromEverAppearingAgain);
-    if (!_dirty || !_mounted)
-      return;
-
-    assert(root != null);
-    _sync(null, _slot);
-  }
-
-  void scheduleBuild() {
-    setState(() {});
-  }
-
-  void setState(Function fn()) {
-    assert(!_disqualifiedFromEverAppearingAgain);
-    _stateful = true;
-    fn();
-    if (_isBuilding || _dirty || !_mounted)
-      return;
-
-    _dirty = true;
-    _scheduleComponentForRender(this);
-  }
-
-  UINode build();
-
-}
-
-class Container extends Component {
-
-  Container({
-    Object key,
-    this.child,
-    this.constraints,
-    this.decoration,
-    this.width,
-    this.height,
-    this.margin,
-    this.padding,
-    this.transform
-  }) : super(key: key);
-
-  final UINode child;
-  final BoxConstraints constraints;
-  final BoxDecoration decoration;
-  final EdgeDims margin;
-  final EdgeDims padding;
-  final Matrix4 transform;
-  final double width;
-  final double height;
-
-  UINode build() {
-    UINode current = child;
-
-    if (child == null && width == null && height == null)
-      current = new SizedBox();
-
-    if (padding != null)
-      current = new Padding(padding: padding, child: current);
-
-    if (decoration != null)
-      current = new DecoratedBox(decoration: decoration, child: current);
-
-    if (width != null || height != null)
-      current = new SizedBox(
-        width: width == null ? double.INFINITY : width,
-        height: height == null ? double.INFINITY : height,
-        child: current
-      );
-
-    if (constraints != null)
-      current = new ConstrainedBox(constraints: constraints, child: current);
-
-    if (margin != null)
-      current = new Padding(padding: margin, child: current);
-
-    if (transform != null)
-      current = new Transform(transform: transform, child: current);
-
-    return current;
-  }
-
-}
 
 class UINodeAppView extends AppView {
 
   UINodeAppView() {
     assert(_appView == null);
   }
 
   static UINodeAppView _appView;
   static void initUINodeAppView() {
     if (_appView == null)
@@ skipping 53 matching lines @@
       // we haven't attached it yet
       UINodeAppView._appView.root = root;
     }
     assert(root.parent is RenderView);
   }
 
 }
 
 typedef UINode Builder();
 
-class RenderNodeToUINodeAdapter extends AbstractUINodeRoot {
+class RenderObjectToUINodeAdapter extends AbstractUINodeRoot {
 
-  RenderNodeToUINodeAdapter(
+  RenderObjectToUINodeAdapter(
     RenderObjectWithChildMixin<RenderBox> container,
     this.builder
   ) : _container = container {
     assert(builder != null);
   }
 
   RenderObjectWithChildMixin<RenderBox> _container;
   RenderObjectWithChildMixin<RenderBox> get container => _container;
   void set container(RenderObjectWithChildMixin<RenderBox> value) {
     if (_container != value) {
@@ skipping 18 matching lines @@
       // we haven't attached it yet
       assert(_container.child == null);
       _container.child = root;
     }
     assert(root.parent == _container);
   }
 
   UINode build() => builder();
 
 }