Re-land Expose height and width factor in AnimatedAlign (#61136)

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

@@ -882,10 +882,14 @@ class AnimatedAlign extends ImplicitlyAnimatedWidget {
     Key key,
     @required this.alignment,
     this.child,
+    this.heightFactor,
+    this.widthFactor,
     Curve curve = Curves.linear,
     @required Duration duration,
     VoidCallback onEnd,
   }) : assert(alignment != null),
+       assert(widthFactor == null || widthFactor >= 0.0),
+       assert(heightFactor == null || heightFactor >= 0.0),
        super(key: key, curve: curve, duration: duration, onEnd: onEnd);
 
   /// How to align the child.
@@ -911,6 +915,16 @@ class AnimatedAlign extends ImplicitlyAnimatedWidget {
   /// {@macro flutter.widgets.child}
   final Widget child;
 
+  /// If non-null, sets its height to the child's height multiplied by this factor.
+  ///
+  /// Must be greater than or equal to 0.0, defaults to null.
+  final double heightFactor;
+
+  /// If non-null, sets its width to the child's width multiplied by this factor.
+  ///
+  /// Must be greater than or equal to 0.0, defaults to null.
+  final double widthFactor;
+
   @override
   _AnimatedAlignState createState() => _AnimatedAlignState();
 
@@ -923,16 +937,26 @@ class AnimatedAlign extends ImplicitlyAnimatedWidget {
 
 class _AnimatedAlignState extends AnimatedWidgetBaseState<AnimatedAlign> {
   AlignmentGeometryTween _alignment;
+  Tween<double> _heightFactorTween;
+  Tween<double> _widthFactorTween;
 
   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
     _alignment = visitor(_alignment, widget.alignment, (dynamic value) => AlignmentGeometryTween(begin: value as AlignmentGeometry)) as AlignmentGeometryTween;
+    if(widget.heightFactor != null) {
+      _heightFactorTween = visitor(_heightFactorTween, widget.heightFactor, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    }
+    if(widget.widthFactor != null) {
+      _widthFactorTween = visitor(_widthFactorTween, widget.widthFactor, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    }
   }
 
   @override
   Widget build(BuildContext context) {
     return Align(
       alignment: _alignment.evaluate(animation),
+      heightFactor: _heightFactorTween?.evaluate(animation),
+      widthFactor: _widthFactorTween?.evaluate(animation),
       child: widget.child,
     );
   }
@@ -941,6 +965,8 @@ class _AnimatedAlignState extends AnimatedWidgetBaseState<AnimatedAlign> {
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
     description.add(DiagnosticsProperty<AlignmentGeometryTween>('alignment', _alignment, defaultValue: null));
+    description.add(DiagnosticsProperty<Tween<double>>('widthFactor', _widthFactorTween, defaultValue: null));
+    description.add(DiagnosticsProperty<Tween<double>>('heightFactor', _heightFactorTween, defaultValue: null));
   }
 }
 

packages/flutter/test/widgets/align_test.dart

@@ -112,4 +112,51 @@ void main() {
     expect(size.width, equals(800.0));
     expect(size.height, equals(10.0));
   });
+
+  testWidgets('Align widthFactor', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: Row(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: <Widget>[
+            Align(
+              widthFactor: 0.5,
+              child: Container(
+                height: 100.0,
+                width: 100.0,
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+    final RenderBox box = tester.renderObject<RenderBox>(find.byType(Align));
+    expect(box.size.width, equals(50.0));
+  });
+
+  testWidgets('Align heightFactor', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: <Widget>[
+            Align(
+              alignment: Alignment.center,
+              heightFactor: 0.5,
+              child: Container(
+                height: 100.0,
+                width: 100.0,
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+    final RenderBox box = tester.renderObject<RenderBox>(find.byType(Align));
+    expect(box.size.height, equals(50.0));
+  });
 }

packages/flutter/test/widgets/animated_align_test.dart

@@ -59,4 +59,104 @@ void main() {
     expect(tester.getSize(find.byKey(target)), const Size(100.0, 200.0));
     expect(tester.getTopRight(find.byKey(target)), const Offset(800.0, 400.0));
   });
+
+  testWidgets('AnimatedAlign widthFactor', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: Row(
+          mainAxisSize: MainAxisSize.min,
+          children: <Widget>[
+            AnimatedAlign(
+              alignment: Alignment.center,
+              curve: Curves.ease,
+              widthFactor: 0.5,
+              duration: const Duration(milliseconds: 200),
+              child: Container(
+                height: 100.0,
+                width: 100.0,
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+    final RenderBox box = tester.renderObject<RenderBox>(find.byType(AnimatedAlign));
+    expect(box.size.width, equals(50.0));
+  });
+
+  testWidgets('AnimatedAlign heightFactor', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: Column(
+          children: <Widget>[
+            AnimatedAlign(
+              alignment: Alignment.center,
+              curve: Curves.ease,
+              heightFactor: 0.5,
+              duration: const Duration(milliseconds: 200),
+              child: Container(
+                height: 100.0,
+                width: 100.0,
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+    final RenderBox box = tester.renderObject<RenderBox>(find.byType(AnimatedAlign));
+    expect(box.size.height, equals( 50.0));
+  });
+
+  testWidgets('AnimatedAlign null height factor', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: <Widget>[
+            AnimatedAlign(
+              alignment: Alignment.center,
+              curve: Curves.ease,
+              duration: const Duration(milliseconds: 200),
+              child: Container(
+                height: 100.0,
+                width: 100.0,
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+    final RenderBox box = tester.renderObject<RenderBox>(find.byType(Container));
+    expect(box.size, equals(const Size(100.0, 100)));
+  });
+
+  testWidgets('AnimatedAlign null widthFactor', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: SizedBox.shrink(
+          child: Row(
+            mainAxisSize: MainAxisSize.min,
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+               AnimatedAlign(
+                alignment: Alignment.center,
+                curve: Curves.ease,
+                duration: const Duration(milliseconds: 200),
+                child: Container(
+                  height: 100.0,
+                  width: 100.0,
+                ),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+    final RenderBox box = tester.renderObject<RenderBox>(find.byType(Container));
+    expect(box.size, equals(const Size(100.0, 100)));
+  });
 }