Replace Align shrinkWrap parameter with widthFactor and heightFactor

examples/widgets/scrollbar.dart

@@ -33,7 +33,8 @@ class ScrollbarAppState extends State<ScrollbarApp> {
     Widget scrollable = new Container(
       margin: new EdgeDims.symmetric(horizontal: 6.0), // TODO(hansmuller) 6.0 should be based on _kScrollbarThumbWidth
       child: new Center(
-        shrinkWrap: ShrinkWrap.both,
+        widthFactor: 1.0,
+        heightFactor: 1.0,
         child: new Container(
           width: 80.0,
           height: _itemExtent * 5.0,

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

@@ -92,7 +92,7 @@ abstract class MaterialButtonState<T extends MaterialButton> extends State<T> {
     Widget contents = new Container(
       padding: new EdgeDims.symmetric(horizontal: 8.0),
       child: new Center(
-        shrinkWrap: ShrinkWrap.width,
+        widthFactor: 1.0,
         child: config.child
       )
     );

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

@@ -344,7 +344,7 @@ class Tab extends StatelessComponent {
     }
 
     Container centeredLabel = new Container(
-      child: new Center(child: labelContent, shrinkWrap: ShrinkWrap.both),
+      child: new Center(child: labelContent, widthFactor: 1.0, heightFactor: 1.0),
       constraints: new BoxConstraints(minWidth: _kMinTabWidth),
       padding: _kTabLabelPadding
     );

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

@@ -143,13 +143,6 @@ class RenderPadding extends RenderShiftedBox {
   }
 }
 
-enum ShrinkWrap {
-  width,
-  height,
-  both,
-  none
-}
-
 class RenderPositionedBox extends RenderShiftedBox {
 
   // This box aligns a child box within itself. It's only useful for
@@ -161,12 +154,13 @@ class RenderPositionedBox extends RenderShiftedBox {
   RenderPositionedBox({
     RenderBox child,
     FractionalOffset alignment: const FractionalOffset(0.5, 0.5),
-    ShrinkWrap shrinkWrap: ShrinkWrap.none
+    double widthFactor,
+    double heightFactor
   }) : _alignment = alignment,
-       _shrinkWrap = shrinkWrap,
+       _widthFactor = widthFactor,
+       _heightFactor = heightFactor,
        super(child) {
     assert(alignment != null);
-    assert(shrinkWrap != null);
   }
 
   FractionalOffset get alignment => _alignment;
@@ -179,31 +173,40 @@ class RenderPositionedBox extends RenderShiftedBox {
     markNeedsLayout();
   }
 
-  ShrinkWrap _shrinkWrap;
-  ShrinkWrap get shrinkWrap => _shrinkWrap;
-  void set shrinkWrap (ShrinkWrap value) {
-    assert(value != null);
-    if (_shrinkWrap == value)
+  double _widthFactor;
+  double get widthFactor => _widthFactor;
+  void set widthFactor (double value) {
+    if (_widthFactor == value)
       return;
-    _shrinkWrap = value;
+    _widthFactor = value;
     markNeedsLayout();
   }
 
-  // These are only valid during performLayout() and paint(), since they rely on constraints which is only set after layout() is called.
-  bool get _shinkWrapWidth => _shrinkWrap == ShrinkWrap.width || _shrinkWrap == ShrinkWrap.both || constraints.maxWidth == double.INFINITY;
-  bool get _shinkWrapHeight => _shrinkWrap == ShrinkWrap.height || _shrinkWrap == ShrinkWrap.both || constraints.maxHeight == double.INFINITY;
+  double _heightFactor;
+  double get heightFactor => _heightFactor;
+  void set heightFactor (double value) {
+    if (_heightFactor == value)
+      return;
+    _heightFactor = value;
+    markNeedsLayout();
+  }
 
   void performLayout() {
+    final bool shrinkWrapWidth = widthFactor != null || constraints.maxWidth == double.INFINITY;
+    final bool shrinkWrapHeight = heightFactor != null || constraints.maxHeight == double.INFINITY;
+
     if (child != null) {
       child.layout(constraints.loosen(), parentUsesSize: true);
-      size = constraints.constrain(new Size(_shinkWrapWidth ? child.size.width : double.INFINITY,
-                                            _shinkWrapHeight ? child.size.height : double.INFINITY));
-      Offset delta = size - child.size;
+      final Size desiredSize = new Size(child.size.width * (_widthFactor ?? 1.0),
+                                        child.size.height * (_heightFactor ?? 1.0));
+      size = constraints.constrain(new Size(shrinkWrapWidth ? desiredSize.width : double.INFINITY,
+                                            shrinkWrapHeight ? desiredSize.height : double.INFINITY));
+      final Offset delta = size - desiredSize;
       final BoxParentData childParentData = child.parentData;
-      childParentData.position = (delta.scale(_alignment.x, _alignment.y)).toPoint();
+      childParentData.position = delta.scale(_alignment.x, _alignment.y).toPoint();
     } else {
-      size = constraints.constrain(new Size(_shinkWrapWidth ? 0.0 : double.INFINITY,
-                                            _shinkWrapHeight ? 0.0 : double.INFINITY));
+      size = constraints.constrain(new Size(shrinkWrapWidth ? 0.0 : double.INFINITY,
+                                            shrinkWrapHeight ? 0.0 : double.INFINITY));
     }
   }
 

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

@@ -48,7 +48,6 @@ export 'package:flutter/rendering.dart' show
     Rect,
     ScrollDirection,
     Shape,
-    ShrinkWrap,
     Size,
     StyledTextSpan,
     TextAlign,
@@ -238,26 +237,27 @@ class Align extends OneChildRenderObjectWidget {
   Align({
     Key key,
     this.alignment: const FractionalOffset(0.5, 0.5),
-    this.shrinkWrap: ShrinkWrap.none,
+    this.widthFactor,
+    this.heightFactor,
     Widget child
-  }) : super(key: key, child: child) {
-    assert(shrinkWrap != null);
-  }
+  }) : super(key: key, child: child);
 
   final FractionalOffset alignment;
-  final ShrinkWrap shrinkWrap;
+  final double widthFactor;
+  final double heightFactor;
 
-  RenderPositionedBox createRenderObject() => new RenderPositionedBox(alignment: alignment, shrinkWrap: shrinkWrap);
+  RenderPositionedBox createRenderObject() => new RenderPositionedBox(alignment: alignment, widthFactor: widthFactor, heightFactor: heightFactor);
 
   void updateRenderObject(RenderPositionedBox renderObject, Align oldWidget) {
     renderObject.alignment = alignment;
-    renderObject.shrinkWrap = shrinkWrap;
+    renderObject.widthFactor = widthFactor;
+    renderObject.heightFactor = heightFactor;
   }
 }
 
 class Center extends Align {
-  Center({ Key key, ShrinkWrap shrinkWrap: ShrinkWrap.none, Widget child })
-    : super(key: key, shrinkWrap: shrinkWrap, child: child);
+  Center({ Key key, widthFactor, heightFactor, Widget child })
+    : super(key: key, widthFactor: widthFactor, heightFactor: heightFactor, child: child);
 }
 
 class CustomOneChildLayout extends OneChildRenderObjectWidget {

packages/unit/test/rendering/positioned_box_test.dart

@@ -21,22 +21,49 @@ void main() {
       additionalConstraints: new BoxConstraints.tight(new Size(100.0, 100.0)),
       child: new RenderDecoratedBox(decoration: new BoxDecoration())
     );
-    RenderPositionedBox positioner = new RenderPositionedBox(child: sizer, shrinkWrap: ShrinkWrap.width);
+    RenderPositionedBox positioner = new RenderPositionedBox(child: sizer, widthFactor: 1.0);
     layout(positioner, constraints: new BoxConstraints.loose(new Size(200.0, 200.0)));
 
     expect(positioner.size.width, equals(100.0), reason: "positioner width");
     expect(positioner.size.height, equals(200.0), reason: "positioner height");
 
-    positioner.shrinkWrap = ShrinkWrap.height;
+    positioner.widthFactor = null;
+    positioner.heightFactor = 1.0;
     pumpFrame();
 
     expect(positioner.size.width, equals(200.0), reason: "positioner width");
     expect(positioner.size.height, equals(100.0), reason: "positioner height");
 
-    positioner.shrinkWrap = ShrinkWrap.both;
+    positioner.widthFactor = 1.0;
     pumpFrame();
 
     expect(positioner.size.width, equals(100.0), reason: "positioner width");
     expect(positioner.size.height, equals(100.0), reason: "positioner height");
   });
+
+  test('RenderPositionedBox width and height factors', () {
+    RenderConstrainedBox sizer = new RenderConstrainedBox(
+      additionalConstraints: new BoxConstraints.tight(new Size(100.0, 100.0)),
+      child: new RenderDecoratedBox(decoration: new BoxDecoration())
+    );
+    RenderPositionedBox positioner = new RenderPositionedBox(child: sizer, widthFactor: 1.0, heightFactor: 0.0);
+    layout(positioner, constraints: new BoxConstraints.loose(new Size(200.0, 200.0)));
+
+    expect(positioner.size.width, equals(100.0));
+    expect(positioner.size.height, equals(0.0));
+
+    positioner.widthFactor = 0.5;
+    positioner.heightFactor = 0.5;
+    pumpFrame();
+
+    expect(positioner.size.width, equals(50.0));
+    expect(positioner.size.height, equals(50.0));
+
+    positioner.widthFactor = null;
+    positioner.heightFactor = null;
+    pumpFrame();
+
+    expect(positioner.size.width, equals(200.0));
+    expect(positioner.size.height, equals(200.0));
+  });
 }