SizedBox.expand (#6791)

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

@@ -808,11 +808,20 @@ class CustomMultiChildLayout extends MultiChildRenderObjectWidget {
 ///
 /// If not given a child, this widget will size itself to the given width and
 /// height, treating nulls as zero.
+///
+/// The [new SizedBox.expand] constructor can be used to make a [SizedBox] that
+/// sizes itself to fit the parent. It is equivalent to setting [width] and
+/// [height] to [double.INFINITY].
 class SizedBox extends SingleChildRenderObjectWidget {
   /// Creates a box of a specific size.
   const SizedBox({ Key key, this.width, this.height, Widget child })
     : super(key: key, child: child);
 
+  const SizedBox.expand({ Key key, Widget child })
+    : width = double.INFINITY,
+      height = double.INFINITY,
+      super(key: key, child: child);
+
   /// If non-null, requires the child to have exactly this width.
   final double width;
 
@@ -833,13 +842,22 @@ class SizedBox extends SingleChildRenderObjectWidget {
     renderObject.additionalConstraints = _additionalConstraints;
   }
 
+  @override
+  String toStringShort() {
+    String type = (width == double.INFINITY && height == double.INFINITY) ?
+                  '$runtimeType.expand' : '$runtimeType';
+    return key == null ? '$type' : '$type-$key';
+  }
+
   @override
   void debugFillDescription(List<String> description) {
     super.debugFillDescription(description);
-    if (width != null)
-      description.add('width: $width');
-    if (height != null)
-      description.add('height: $height');
+    if (width != double.INFINITY || height != double.INFINITY) {
+      if (width != null)
+        description.add('width: $width');
+      if (height != null)
+        description.add('height: $height');
+    }
   }
 }
 

packages/flutter/test/widgets/sized_box_test.dart

+// Copyright 2016 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 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('SizedBox - no child', (WidgetTester tester) async {
+    GlobalKey patient = new GlobalKey();
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox(
+          key: patient,
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(0.0, 0.0)));
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox(
+          key: patient,
+          height: 0.0,
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(0.0, 0.0)));
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox(
+          key: patient,
+          width: 0.0,
+          height: 0.0,
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(0.0, 0.0)));
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox(
+          key: patient,
+          width: 100.0,
+          height: 100.0,
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(100.0, 100.0)));
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox(
+          key: patient,
+          width: 1000.0,
+          height: 1000.0,
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(800.0, 600.0)));
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox.expand(
+          key: patient,
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(800.0, 600.0)));
+  });
+
+  testWidgets('SizedBox - container child', (WidgetTester tester) async {
+    GlobalKey patient = new GlobalKey();
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox(
+          key: patient,
+          child: new Container(),
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(800.0, 600.0)));
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox(
+          key: patient,
+          height: 0.0,
+          child: new Container(),
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(800.0, 0.0)));
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox(
+          key: patient,
+          width: 0.0,
+          height: 0.0,
+          child: new Container(),
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(0.0, 0.0)));
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox(
+          key: patient,
+          width: 100.0,
+          height: 100.0,
+          child: new Container(),
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(100.0, 100.0)));
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox(
+          key: patient,
+          width: 1000.0,
+          height: 1000.0,
+          child: new Container(),
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(800.0, 600.0)));
+
+    await tester.pumpWidget(
+      new Center(
+        child: new SizedBox.expand(
+          key: patient,
+          child: new Container(),
+        )
+      )
+    );
+    expect(patient.currentContext.size, equals(const Size(800.0, 600.0)));
+  });
+}