Add AnimatedPositionedDirectional (#12228)

This widget makes it easier to animated Positioned widgets with
awareness of the ambient Directionality.

Fixes #11998

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

@@ -416,11 +416,7 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
           child: new Center(
             child: new Stack(
               children: <Widget>[
-                new Positioned(
+                new Positioned.fill(
-                  left: 0.0,
-                  top: 0.0,
-                  right: 0.0,
-                  bottom: 0.0,
                   child: new CustomPaint(
                     painter: new _RadialPainter(
                       circles: _circles.toList(),

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

@@ -464,8 +464,8 @@ class InputDecorator extends StatelessWidget {
         top += topPaddingIncrement + baseStyle.fontSize - labelStyle.fontSize;
 
       stackChildren.add(
-        new AnimatedPositioned(
+        new AnimatedPositionedDirectional(
-          left: 0.0,
+          start: 0.0,
           top: top,
           duration: _kTransitionDuration,
           curve: _kTransitionCurve,

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

@@ -482,6 +482,11 @@ class _AnimatedContainerState extends AnimatedWidgetBaseState<AnimatedContainer>
 /// position over a given duration whenever the given position changes.
 ///
 /// Only works if it's the child of a [Stack].
+///
+/// See also:
+///
+///  * [AnimatedPositionedDirectional], which adapts to the ambient
+///    [Directionality].
 class AnimatedPositioned extends ImplicitlyAnimatedWidget {
   /// Creates a widget that animates its position implicitly.
   ///
@@ -608,6 +613,123 @@ class _AnimatedPositionedState extends AnimatedWidgetBaseState<AnimatedPositione
   }
 }
 
+/// Animated version of [PositionedDirectional] which automatically transitions the child's
+/// position over a given duration whenever the given position changes.
+///
+/// Only works if it's the child of a [Stack].
+///
+/// See also:
+///
+///  * [AnimatedPositioned], which specifies the widget's position visually.
+class AnimatedPositionedDirectional extends ImplicitlyAnimatedWidget {
+  /// Creates a widget that animates its position implicitly.
+  ///
+  /// Only two out of the three horizontal values ([start], [end],
+  /// [width]), and only two out of the three vertical values ([top],
+  /// [bottom], [height]), can be set. In each case, at least one of
+  /// the three must be null.
+  ///
+  /// The [curve] and [duration] arguments must not be null.
+  const AnimatedPositionedDirectional({
+    Key key,
+    @required this.child,
+    this.start,
+    this.top,
+    this.end,
+    this.bottom,
+    this.width,
+    this.height,
+    Curve curve: Curves.linear,
+    @required Duration duration,
+  }) : assert(start == null || end == null || width == null),
+       assert(top == null || bottom == null || height == null),
+      super(key: key, curve: curve, duration: duration);
+
+  /// The widget below this widget in the tree.
+  final Widget child;
+
+  /// The offset of the child's start edge from the start of the stack.
+  final double start;
+
+  /// The offset of the child's top edge from the top of the stack.
+  final double top;
+
+  /// The offset of the child's end edge from the end of the stack.
+  final double end;
+
+  /// The offset of the child's bottom edge from the bottom of the stack.
+  final double bottom;
+
+  /// The child's width.
+  ///
+  /// Only two out of the three horizontal values (start, end, width) can be
+  /// set. The third must be null.
+  final double width;
+
+  /// The child's height.
+  ///
+  /// Only two out of the three vertical values (top, bottom, height) can be
+  /// set. The third must be null.
+  final double height;
+
+  @override
+  _AnimatedPositionedDirectionalState createState() => new _AnimatedPositionedDirectionalState();
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder description) {
+    super.debugFillProperties(description);
+    description.add(new DoubleProperty('start', start, defaultValue: null));
+    description.add(new DoubleProperty('top', top, defaultValue: null));
+    description.add(new DoubleProperty('end', end, defaultValue: null));
+    description.add(new DoubleProperty('bottom', bottom, defaultValue: null));
+    description.add(new DoubleProperty('width', width, defaultValue: null));
+    description.add(new DoubleProperty('height', height, defaultValue: null));
+  }
+}
+
+class _AnimatedPositionedDirectionalState extends AnimatedWidgetBaseState<AnimatedPositionedDirectional> {
+  Tween<double> _start;
+  Tween<double> _top;
+  Tween<double> _end;
+  Tween<double> _bottom;
+  Tween<double> _width;
+  Tween<double> _height;
+
+  @override
+  void forEachTween(TweenVisitor<dynamic> visitor) {
+    _start = visitor(_start, widget.start, (dynamic value) => new Tween<double>(begin: value));
+    _top = visitor(_top, widget.top, (dynamic value) => new Tween<double>(begin: value));
+    _end = visitor(_end, widget.end, (dynamic value) => new Tween<double>(begin: value));
+    _bottom = visitor(_bottom, widget.bottom, (dynamic value) => new Tween<double>(begin: value));
+    _width = visitor(_width, widget.width, (dynamic value) => new Tween<double>(begin: value));
+    _height = visitor(_height, widget.height, (dynamic value) => new Tween<double>(begin: value));
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return new PositionedDirectional(
+      child: widget.child,
+      start: _start?.evaluate(animation),
+      top: _top?.evaluate(animation),
+      end: _end?.evaluate(animation),
+      bottom: _bottom?.evaluate(animation),
+      width: _width?.evaluate(animation),
+      height: _height?.evaluate(animation)
+    );
+  }
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder description) {
+    super.debugFillProperties(description);
+    description.add(new ObjectFlagProperty<Tween<double>>.has('start', _start));
+    description.add(new ObjectFlagProperty<Tween<double>>.has('top', _top));
+    description.add(new ObjectFlagProperty<Tween<double>>.has('end', _end));
+    description.add(new ObjectFlagProperty<Tween<double>>.has('bottom', _bottom));
+    description.add(new ObjectFlagProperty<Tween<double>>.has('width', _width));
+    description.add(new ObjectFlagProperty<Tween<double>>.has('height', _height));
+  }
+}
+
 /// Animated version of [Opacity] which automatically transitions the child's
 /// opacity over a given duration whenever the given opacity changes.
 ///

packages/flutter/test/widgets/animated_positioned_test.dart

@@ -20,7 +20,7 @@ void main() {
     expect(positioned, hasOneLineDescription);
   });
 
-  testWidgets('AnimatedPositioned - basics', (WidgetTester tester) async {
+  testWidgets('AnimatedPositioned - basics (VISUAL)', (WidgetTester tester) async {
     final GlobalKey key = new GlobalKey();
 
     RenderBox box;
@@ -35,10 +35,10 @@ void main() {
             top: 30.0,
             width: 70.0,
             height: 110.0,
-            duration: const Duration(seconds: 2)
+            duration: const Duration(seconds: 2),
-          )
+          ),
-        ]
+        ],
-      )
+      ),
     );
 
     box = key.currentContext.findRenderObject();
@@ -59,25 +59,27 @@ void main() {
             top: 31.0,
             width: 59.0,
             height: 71.0,
-            duration: const Duration(seconds: 2)
+            duration: const Duration(seconds: 2),
-          )
+          ),
-        ]
+        ],
-      )
+      ),
     );
 
+    const Offset first = const Offset(50.0 + 70.0 / 2.0, 30.0 + 110.0 / 2.0);
+    const Offset last = const Offset(37.0 + 59.0 / 2.0, 31.0 + 71.0 / 2.0);
+
     box = key.currentContext.findRenderObject();
-    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(const Offset(50.0 + 70.0 / 2.0, 30.0 + 110.0 / 2.0)));
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(first));
 
     await tester.pump(const Duration(seconds: 1));
 
     box = key.currentContext.findRenderObject();
-    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(const Offset(50.0 - (50.0 - 37.0) / 2.0 + (70.0 - (70.0 - 59.0) / 2.0) / 2.0,
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(Offset.lerp(first, last, 0.5)));
-                                                                                30.0 + (31.0 - 30.0) / 2.0 + (110.0 - (110.0 - 71.0) / 2.0) / 2.0)));
 
     await tester.pump(const Duration(seconds: 1));
 
     box = key.currentContext.findRenderObject();
-    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(const Offset(37.0 + 59.0 / 2.0, 31.0 + 71.0 / 2.0)));
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(last));
 
     expect(box, hasAGoodToStringDeep);
     expect(
@@ -100,6 +102,178 @@ void main() {
     );
   });
 
+  testWidgets('AnimatedPositioned - basics (LTR)', (WidgetTester tester) async {
+    final GlobalKey key = new GlobalKey();
+
+    RenderBox box;
+
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Stack(
+          children: <Widget>[
+            new AnimatedPositionedDirectional(
+              child: new Container(key: key),
+              start: 50.0,
+              top: 30.0,
+              width: 70.0,
+              height: 110.0,
+              duration: const Duration(seconds: 2),
+            ),
+          ],
+        ),
+      ),
+    );
+
+    box = key.currentContext.findRenderObject();
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(const Offset(50.0 + 70.0 / 2.0, 30.0 + 110.0 / 2.0)));
+
+    await tester.pump(const Duration(seconds: 1));
+
+    box = key.currentContext.findRenderObject();
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(const Offset(50.0 + 70.0 / 2.0, 30.0 + 110.0 / 2.0)));
+
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Stack(
+          children: <Widget>[
+            new AnimatedPositionedDirectional(
+              child: new Container(key: key),
+              start: 37.0,
+              top: 31.0,
+              width: 59.0,
+              height: 71.0,
+              duration: const Duration(seconds: 2),
+            ),
+          ],
+        ),
+      ),
+    );
+
+    const Offset first = const Offset(50.0 + 70.0 / 2.0, 30.0 + 110.0 / 2.0);
+    const Offset last = const Offset(37.0 + 59.0 / 2.0, 31.0 + 71.0 / 2.0);
+
+    box = key.currentContext.findRenderObject();
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(first));
+
+    await tester.pump(const Duration(seconds: 1));
+
+    box = key.currentContext.findRenderObject();
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(Offset.lerp(first, last, 0.5)));
+
+    await tester.pump(const Duration(seconds: 1));
+
+    box = key.currentContext.findRenderObject();
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(last));
+
+    expect(box, hasAGoodToStringDeep);
+    expect(
+      box.toStringDeep(minLevel: DiagnosticLevel.info),
+      equalsIgnoringHashCodes(
+        'RenderLimitedBox#00000\n'
+        ' │ parentData: top=31.0; left=37.0; width=59.0; height=71.0;\n'
+        ' │   offset=Offset(37.0, 31.0) (can use size)\n'
+        ' │ constraints: BoxConstraints(w=59.0, h=71.0)\n'
+        ' │ size: Size(59.0, 71.0)\n'
+        ' │ maxWidth: 0.0\n'
+        ' │ maxHeight: 0.0\n'
+        ' │\n'
+        ' └─child: RenderConstrainedBox#00000\n'
+        '     parentData: <none> (can use size)\n'
+        '     constraints: BoxConstraints(w=59.0, h=71.0)\n'
+        '     size: Size(59.0, 71.0)\n'
+        '     additionalConstraints: BoxConstraints(biggest)\n',
+      ),
+    );
+  });
+
+  testWidgets('AnimatedPositioned - basics (RTL)', (WidgetTester tester) async {
+    final GlobalKey key = new GlobalKey();
+
+    RenderBox box;
+
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.rtl,
+        child: new Stack(
+          children: <Widget>[
+            new AnimatedPositionedDirectional(
+              child: new Container(key: key),
+              start: 50.0,
+              top: 30.0,
+              width: 70.0,
+              height: 110.0,
+              duration: const Duration(seconds: 2),
+            ),
+          ],
+        ),
+      ),
+    );
+
+    box = key.currentContext.findRenderObject();
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(const Offset(800.0 - 50.0 - 70.0 / 2.0, 30.0 + 110.0 / 2.0)));
+
+    await tester.pump(const Duration(seconds: 1));
+
+    box = key.currentContext.findRenderObject();
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(const Offset(800.0 - 50.0 - 70.0 / 2.0, 30.0 + 110.0 / 2.0)));
+
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.rtl,
+        child: new Stack(
+          children: <Widget>[
+            new AnimatedPositionedDirectional(
+              child: new Container(key: key),
+              start: 37.0,
+              top: 31.0,
+              width: 59.0,
+              height: 71.0,
+              duration: const Duration(seconds: 2),
+            ),
+          ],
+        ),
+      ),
+    );
+
+    const Offset first = const Offset(800.0 - 50.0 - 70.0 / 2.0, 30.0 + 110.0 / 2.0);
+    const Offset last = const Offset(800.0 - 37.0 - 59.0 / 2.0, 31.0 + 71.0 / 2.0);
+
+    box = key.currentContext.findRenderObject();
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(first));
+
+    await tester.pump(const Duration(seconds: 1));
+
+    box = key.currentContext.findRenderObject();
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(Offset.lerp(first, last, 0.5)));
+
+    await tester.pump(const Duration(seconds: 1));
+
+    box = key.currentContext.findRenderObject();
+    expect(box.localToGlobal(box.size.center(Offset.zero)), equals(last));
+
+    expect(box, hasAGoodToStringDeep);
+    expect(
+      box.toStringDeep(minLevel: DiagnosticLevel.info),
+      equalsIgnoringHashCodes(
+        'RenderLimitedBox#00000\n'
+        ' │ parentData: top=31.0; right=37.0; width=59.0; height=71.0;\n'
+        ' │   offset=Offset(704.0, 31.0) (can use size)\n'
+        ' │ constraints: BoxConstraints(w=59.0, h=71.0)\n'
+        ' │ size: Size(59.0, 71.0)\n'
+        ' │ maxWidth: 0.0\n'
+        ' │ maxHeight: 0.0\n'
+        ' │\n'
+        ' └─child: RenderConstrainedBox#00000\n'
+        '     parentData: <none> (can use size)\n'
+        '     constraints: BoxConstraints(w=59.0, h=71.0)\n'
+        '     size: Size(59.0, 71.0)\n'
+        '     additionalConstraints: BoxConstraints(biggest)\n'
+      ),
+    );
+  });
+
   testWidgets('AnimatedPositioned - interrupted animation', (WidgetTester tester) async {
     final GlobalKey key = new GlobalKey();