Added LayoutId widget, MultiChildLayoutDelegate.isChild()

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

@@ -14,15 +14,10 @@ import 'tool_bar.dart';
 
 const double _kFloatingActionButtonMargin = 16.0; // TODO(hmuller): should be device dependent
 
-const int _kBodyIndex = 0;
-const int _kToolBarIndex = 1;
-const int _kBottomSheetIndex = 2;
-const int _kSnackBarIndex = 3;
-const int _kFloatingActionButtonIndex = 4;
+enum _Child { body, toolBar, bottomSheet, snackBar, floatingActionButton }
 
 class _ScaffoldLayout extends MultiChildLayoutDelegate {
-  void performLayout(Size size, BoxConstraints constraints, int childCount) {
-    assert(childCount == 5);
+  void performLayout(Size size, BoxConstraints constraints) {
 
     // This part of the layout has the same effect as putting the toolbar and
     // body in a column and making the body flexible. What's different is that
@@ -30,12 +25,19 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
     // so the toolbar's shadow is drawn on top of the body.
 
     final BoxConstraints toolBarConstraints = constraints.loosen().tightenWidth(size.width);
-    final Size toolBarSize = layoutChild(_kToolBarIndex, toolBarConstraints);
-    final double bodyHeight = size.height - toolBarSize.height;
-    final BoxConstraints bodyConstraints = toolBarConstraints.tightenHeight(bodyHeight);
-    layoutChild(_kBodyIndex, bodyConstraints);
-    positionChild(_kToolBarIndex, Point.origin);
-    positionChild(_kBodyIndex, new Point(0.0, toolBarSize.height));
+    Size toolBarSize = Size.zero;
+
+    if (isChild(_Child.toolBar)) {
+      toolBarSize = layoutChild(_Child.toolBar, toolBarConstraints);
+      positionChild(_Child.toolBar, Point.origin);
+    }
+
+    if (isChild(_Child.body)) {
+      final double bodyHeight = size.height - toolBarSize.height;
+      final BoxConstraints bodyConstraints = toolBarConstraints.tightenHeight(bodyHeight);
+      layoutChild(_Child.body, bodyConstraints);
+      positionChild(_Child.body, new Point(0.0, toolBarSize.height));
+    }
 
     // The BottomSheet and the SnackBar are anchored to the bottom of the parent,
     // they're as wide as the parent and are given their intrinsic height.
@@ -47,24 +49,39 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
     // by _kFloatingActionButtonMargin.
 
     final BoxConstraints fullWidthConstraints = constraints.loosen().tightenWidth(size.width);
-    final Size bottomSheetSize = layoutChild(_kBottomSheetIndex, fullWidthConstraints);
-    final Size snackBarSize = layoutChild(_kSnackBarIndex, fullWidthConstraints);
-    final Size fabSize = layoutChild(_kFloatingActionButtonIndex, constraints.loosen());
-    positionChild(_kBottomSheetIndex, new Point(0.0, size.height - bottomSheetSize.height));
-    positionChild(_kSnackBarIndex, new Point(0.0, size.height - snackBarSize.height));
-
-    final double fabX = size.width - fabSize.width - _kFloatingActionButtonMargin;
-    double fabY = size.height - fabSize.height - _kFloatingActionButtonMargin;
-    if (snackBarSize.height > 0.0)
-      fabY = math.min(fabY, size.height - snackBarSize.height - fabSize.height - _kFloatingActionButtonMargin);
-    if (bottomSheetSize.height > 0.0)
-      fabY = math.min(fabY, size.height - bottomSheetSize.height - fabSize.height / 2.0);
-    positionChild(_kFloatingActionButtonIndex, new Point(fabX, fabY));
+    Size bottomSheetSize = Size.zero;
+    Size snackBarSize = Size.zero;
+
+    if (isChild(_Child.bottomSheet)) {
+      bottomSheetSize = layoutChild(_Child.bottomSheet, fullWidthConstraints);
+      positionChild(_Child.bottomSheet, new Point(0.0, size.height - bottomSheetSize.height));
+    }
+
+    if (isChild(_Child.snackBar)) {
+      snackBarSize = layoutChild(_Child.snackBar, fullWidthConstraints);
+      positionChild(_Child.snackBar, new Point(0.0, size.height - snackBarSize.height));
+    }
+
+    if (isChild(_Child.floatingActionButton)) {
+      final Size fabSize = layoutChild(_Child.floatingActionButton, constraints.loosen());
+      final double fabX = size.width - fabSize.width - _kFloatingActionButtonMargin;
+      double fabY = size.height - fabSize.height - _kFloatingActionButtonMargin;
+      if (snackBarSize.height > 0.0)
+        fabY = math.min(fabY, size.height - snackBarSize.height - fabSize.height - _kFloatingActionButtonMargin);
+      if (bottomSheetSize.height > 0.0)
+        fabY = math.min(fabY, size.height - bottomSheetSize.height - fabSize.height / 2.0);
+      positionChild(_Child.floatingActionButton, new Point(fabX, fabY));
+    }
   }
 }
 
 final _ScaffoldLayout _scaffoldLayout = new _ScaffoldLayout();
 
+void _addIfNonNull(List<LayoutId> children, Widget child, Object childId) {
+  if (child != null)
+    children.add(new LayoutId(child: child, id: childId));
+}
+
 class Scaffold extends StatelessComponent {
   Scaffold({
     Key key,
@@ -92,14 +109,14 @@ class Scaffold extends StatelessComponent {
         child: snackBar
       );
     }
-    return new CustomMultiChildLayout(<Widget>[
-      materialBody ?? new Container(height: 0.0),
-      paddedToolBar ?? new Container(height: 0.0),
-      bottomSheet ?? new Container(height: 0.0),
-      constrainedSnackBar ?? new Container(height: 0.0),
-      floatingActionButton ?? new Container(height: 0.0)
-    ],
-      delegate: _scaffoldLayout
-    );
+
+    final List<LayoutId>children = new List<LayoutId>();
+    _addIfNonNull(children, materialBody, _Child.body);
+    _addIfNonNull(children, paddedToolBar, _Child.toolBar);
+    _addIfNonNull(children, bottomSheet, _Child.bottomSheet);
+    _addIfNonNull(children, constrainedSnackBar, _Child.snackBar);
+    _addIfNonNull(children, floatingActionButton, _Child.floatingActionButton);
+
+    return new CustomMultiChildLayout(children, delegate: _scaffoldLayout);
   }
 }

packages/flutter/lib/src/rendering/custom_layout.dart

@@ -5,10 +5,12 @@
 import 'box.dart';
 import 'object.dart';
 
-class _MultiChildParentData extends ContainerBoxParentDataMixin<RenderBox> { }
+class MultiChildLayoutParentData extends ContainerBoxParentDataMixin<RenderBox> {
+  Object id;
+}
 
 abstract class MultiChildLayoutDelegate {
-  final List<RenderBox> _indexToChild = <RenderBox>[];
+  final Map<Object, RenderBox> _idToChild = new Map<Object, RenderBox>();
 
   /// Returns the size of this object given the incomming constraints.
   /// The size cannot reflect the instrinsic sizes of the children.
@@ -16,41 +18,47 @@ abstract class MultiChildLayoutDelegate {
   /// can reflect that.
   Size getSize(BoxConstraints constraints) => constraints.biggest;
 
+  /// True if a non-null LayoutChild was provided for the specified id.
+  bool isChild(Object childId) => _idToChild[childId] != null;
+
   /// Ask the child to update its layout within the limits specified by
   /// the constraints parameter. The child's size is returned.
-  Size layoutChild(int childIndex, BoxConstraints constraints) {
-    final RenderBox child = _indexToChild[childIndex];
+  Size layoutChild(Object childId, BoxConstraints constraints) {
+    final RenderBox child = _idToChild[childId];
+    assert(child != null);
     child.layout(constraints, parentUsesSize: true);
     return child.size;
   }
 
   /// Specify the child's origin relative to this origin.
-  void positionChild(int childIndex, Point position) {
-    final RenderBox child = _indexToChild[childIndex];
-    final _MultiChildParentData childParentData = child.parentData;
+  void positionChild(Object childId, Point position) {
+    final RenderBox child = _idToChild[childId];
+    assert(child != null);
+    final MultiChildLayoutParentData childParentData = child.parentData;
     childParentData.position = position;
   }
 
   void _callPerformLayout(Size size, BoxConstraints constraints, RenderBox firstChild) {
     RenderBox child = firstChild;
     while (child != null) {
-      _indexToChild.add(child);
-      final _MultiChildParentData childParentData = child.parentData;
+      final MultiChildLayoutParentData childParentData = child.parentData;
+      assert(childParentData.id != null);
+      _idToChild[childParentData.id] = child;
       child = childParentData.nextSibling;
     }
-    performLayout(size, constraints, _indexToChild.length);
-    _indexToChild.clear();
+    performLayout(size, constraints);
+    _idToChild.clear();
   }
 
   /// Layout and position all children given this widget's size and the specified
   /// constraints. This method must apply layoutChild() to each child. It should
   /// specify the final position of each child with positionChild().
-  void performLayout(Size size, BoxConstraints constraints, int childCount);
+  void performLayout(Size size, BoxConstraints constraints);
 }
 
 class RenderCustomMultiChildLayoutBox extends RenderBox
-  with ContainerRenderObjectMixin<RenderBox, _MultiChildParentData>,
-       RenderBoxContainerDefaultsMixin<RenderBox, _MultiChildParentData> {
+  with ContainerRenderObjectMixin<RenderBox, MultiChildLayoutParentData>,
+       RenderBoxContainerDefaultsMixin<RenderBox, MultiChildLayoutParentData> {
   RenderCustomMultiChildLayoutBox({
     List<RenderBox> children,
     MultiChildLayoutDelegate delegate
@@ -60,8 +68,8 @@ class RenderCustomMultiChildLayoutBox extends RenderBox
   }
 
   void setupParentData(RenderBox child) {
-    if (child.parentData is! _MultiChildParentData)
-      child.parentData = new _MultiChildParentData();
+    if (child.parentData is! MultiChildLayoutParentData)
+      child.parentData = new MultiChildLayoutParentData();
   }
 
   MultiChildLayoutDelegate get delegate => _delegate;

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

@@ -288,6 +288,39 @@ class CustomOneChildLayout extends OneChildRenderObjectWidget {
   }
 }
 
+class LayoutId extends ParentDataWidget {
+  LayoutId({
+    Key key,
+    Widget child,
+    this.id
+  }) : super(key: key, child: child);
+
+  final Object id;
+
+  void debugValidateAncestor(Widget ancestor) {
+    assert(() {
+      'LayoutId must placed inside a CustomMultiChildLayout';
+      return ancestor is CustomMultiChildLayout;
+    });
+  }
+
+  void applyParentData(RenderObject renderObject) {
+    assert(renderObject.parentData is MultiChildLayoutParentData);
+    final MultiChildLayoutParentData parentData = renderObject.parentData;
+    if (parentData.id != id) {
+      parentData.id = id;
+      AbstractNode targetParent = renderObject.parent;
+      if (targetParent is RenderObject)
+        targetParent.markNeedsLayout();
+    }
+  }
+
+  void debugFillDescription(List<String> description) {
+    super.debugFillDescription(description);
+    description.add('id: $id');
+  }
+}
+
 class CustomMultiChildLayout extends MultiChildRenderObjectWidget {
   CustomMultiChildLayout(List<Widget> children, {
     Key key,

packages/unit/test/widget/custom_multi_child_layout_test.dart

@@ -14,16 +14,16 @@ class TestMultiChildLayoutDelegate extends MultiChildLayoutDelegate {
 
   Size performLayoutSize;
   BoxConstraints performLayoutConstraints;
-  int performLayoutChildCount;
   Size performLayoutSize0;
   Size performLayoutSize1;
+  bool performLayoutIsChild;
 
-  void performLayout(Size size, BoxConstraints constraints, int childCount) {
+  void performLayout(Size size, BoxConstraints constraints) {
     performLayoutSize = size;
     performLayoutConstraints = constraints;
-    performLayoutChildCount = childCount;
     performLayoutSize0 = layoutChild(0, constraints);
     performLayoutSize1 = layoutChild(1, constraints);
+    performLayoutIsChild = isChild('fred');
   }
 }
 
@@ -33,8 +33,8 @@ void main() {
       TestMultiChildLayoutDelegate delegate = new TestMultiChildLayoutDelegate();
       tester.pumpWidget(new Center(
         child: new CustomMultiChildLayout([
-          new Container(width: 150.0, height: 100.0),
-          new Container(width: 100.0, height: 200.0)
+          new LayoutId(id: 0, child: new Container(width: 150.0, height: 100.0)),
+          new LayoutId(id: 1, child: new Container(width: 100.0, height: 200.0))
         ],
           delegate: delegate
         )
@@ -51,11 +51,11 @@ void main() {
       expect(delegate.performLayoutConstraints.maxWidth, 800.0);
       expect(delegate.performLayoutConstraints.minHeight, 0.0);
       expect(delegate.performLayoutConstraints.maxHeight, 600.0);
-      expect(delegate.performLayoutChildCount, 2);
       expect(delegate.performLayoutSize0.width, 150.0);
       expect(delegate.performLayoutSize0.height, 100.0);
       expect(delegate.performLayoutSize1.width, 100.0);
       expect(delegate.performLayoutSize1.height, 200.0);
+      expect(delegate.performLayoutIsChild, false);
     });
   });
 }