Added BottomAppBar docked FloatingActionButtonLocations (#16167)

* Added BottomAppBar docked FloationActionButtonLocations

* Moved the startTop FloatingActionButtonLocation to the demo

* fixed a typo

examples/flutter_gallery/lib/demo/material/fab_motion_demo.dart

@@ -19,9 +19,9 @@ class FabMotionDemo extends StatefulWidget {
 
 class _FabMotionDemoState extends State<FabMotionDemo> {
   static const List<FloatingActionButtonLocation> _floatingActionButtonLocations = const <FloatingActionButtonLocation>[
-    FloatingActionButtonLocation.endFloat, 
+    FloatingActionButtonLocation.endFloat,
     FloatingActionButtonLocation.centerFloat,
-    const _TopStartFloatingActionButtonLocation(),
+    const _StartTopFloatingActionButtonLocation(),
   ];
 
   bool _showFab = true;
@@ -29,25 +29,25 @@ class _FabMotionDemoState extends State<FabMotionDemo> {
 
   @override
   Widget build(BuildContext context) {
-    final Widget floatingActionButton = _showFab 
+    final Widget floatingActionButton = _showFab
       ? new Builder(builder: (BuildContext context) {
         // We use a widget builder here so that this inner context can find the Scaffold.
         // This makes it possible to show the snackbar.
         return new FloatingActionButton(
           backgroundColor: Colors.yellow.shade900,
           onPressed: () => _showSnackbar(context),
-          child: const Icon(Icons.add), 
+          child: const Icon(Icons.add),
         );
-      }) 
+      })
       : null;
     return new Scaffold(
       appBar: new AppBar(
-        title: const Text('FAB Location'), 
+        title: const Text('FAB Location'),
         // Add 48dp of space onto the bottom of the appbar.
         // This gives space for the top-start location to attach to without
         // blocking the 'back' button.
         bottom: const PreferredSize(
-          preferredSize: const Size.fromHeight(48.0), 
+          preferredSize: const Size.fromHeight(48.0),
           child: const SizedBox(),
         ),
       ),
@@ -93,8 +93,8 @@ class _FabMotionDemoState extends State<FabMotionDemo> {
 
 // Places the Floating Action Button at the top of the content area of the
 // app, on the border between the body and the app bar.
-class _TopStartFloatingActionButtonLocation extends FloatingActionButtonLocation {
-  const _TopStartFloatingActionButtonLocation();
+class _StartTopFloatingActionButtonLocation extends FloatingActionButtonLocation {
+  const _StartTopFloatingActionButtonLocation();
 
   @override
   Offset getOffset(ScaffoldPrelayoutGeometry scaffoldGeometry) {
@@ -130,7 +130,7 @@ class _TopStartFloatingActionButtonLocation extends FloatingActionButtonLocation
         fabX = startPadding;
         break;
     }
-    // Finally, we'll place the Y coordinate for the Floating Action Button 
+    // Finally, we'll place the Y coordinate for the Floating Action Button
     // at the top of the content body.
     //
     // We want to place the middle of the Floating Action Button on the

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

@@ -12,37 +12,37 @@ import 'scaffold.dart';
 // TODO(hmuller): should be device dependent.
 /// The margin that a [FloatingActionButton] should leave between it and the
 /// edge of the screen.
-/// 
+///
 /// [FloatingActionButtonLocation.endFloat] uses this to set the appropriate margin
 /// between the [FloatingActionButton] and the end of the screen.
-const double kFloatingActionButtonMargin = 16.0; 
+const double kFloatingActionButtonMargin = 16.0;
 
 /// The amount of time the [FloatingActionButton] takes to transition in or out.
-/// 
-/// The [Scaffold] uses this to set the duration of [FloatingActionButton] 
+///
+/// The [Scaffold] uses this to set the duration of [FloatingActionButton]
 /// motion, entrance, and exit animations.
 const Duration kFloatingActionButtonSegue = const Duration(milliseconds: 200);
 
 /// The fraction of a circle the [FloatingActionButton] should turn when it enters.
-/// 
+///
 /// Its value corresponds to 0.125 of a full circle, equivalent to 45 degrees or pi/4 radians.
 const double kFloatingActionButtonTurnInterval = 0.125;
 
 /// An object that defines a position for the [FloatingActionButton]
 /// based on the [Scaffold]'s [ScaffoldPrelayoutGeometry].
-/// 
+///
 /// Flutter provides [FloatingActionButtonLocation]s for the common
 /// [FloatingActionButton] placements in Material Design applications. These
 /// locations are available as static members of this class.
-/// 
+///
 /// See also:
-/// 
+///
 ///  * [FloatingActionButton], which is a circular button typically shown in the
 ///    bottom right corner of the app.
 ///  * [FloatingActionButtonAnimator], which is used to animate the
-///    [Scaffold.floatingActionButton] from one [FloatingActionButtonLocation] to 
+///    [Scaffold.floatingActionButton] from one [FloatingActionButtonLocation] to
 ///    another.
-///  * [ScaffoldPrelayoutGeometry], the geometry that 
+///  * [ScaffoldPrelayoutGeometry], the geometry that
 ///    [FloatingActionButtonLocation]s use to position the [FloatingActionButton].
 abstract class FloatingActionButtonLocation {
   /// Abstract const constructor. This constructor enables subclasses to provide
@@ -50,15 +50,39 @@ abstract class FloatingActionButtonLocation {
   const FloatingActionButtonLocation();
 
   /// End-aligned [FloatingActionButton], floating at the bottom of the screen.
-  /// 
+  ///
   /// This is the default alignment of [FloatingActionButton]s in Material applications.
   static const FloatingActionButtonLocation endFloat = const _EndFloatFabLocation();
 
   /// Centered [FloatingActionButton], floating at the bottom of the screen.
   static const FloatingActionButtonLocation centerFloat = const _CenterFloatFabLocation();
 
+  /// End-aligned [FloatingActionButton], floating over the
+  /// [Scaffold.bottomNavigationBar] so that the center of the floating
+  /// action button lines up with the top of the bottom navigation bar.
+  ///
+  /// If the value of [Scaffold.bottomNavigationBar] is a [BottomAppBar],
+  /// the bottom app bar can include a "notch" in its shape that accommodates
+  /// the overlapping floating action button.
+  ///
+  /// This is unlikely to be a useful location for apps that lack a bottom
+  /// navigation bar.
+  static FloatingActionButtonLocation endDocked = const _EndDockedFloatingActionButtonLocation();
+
+  /// Center-aligned [FloatingActionButton], floating over the
+  /// [Scaffold.bottomNavigationBar] so that the center of the floating
+  /// action button lines up with the top of the bottom navigation bar.
+  ///
+  /// If the value of [Scaffold.bottomNavigationBar] is a [BottomAppBar],
+  /// the bottom app bar can include a "notch" in its shape that accomodates
+  /// the overlapping floating action button.
+  ///
+  /// This is unlikely to be a useful location for apps that lack a bottom
+  /// navigation bar.
+  static FloatingActionButtonLocation centerDocked = const _CenterDockedFloatingActionButtonLocation();
+
   /// Places the [FloatingActionButton] based on the [Scaffold]'s layout.
-  /// 
+  ///
   /// This uses a [ScaffoldPrelayoutGeometry], which the [Scaffold] constructs
   /// during its layout phase after it has laid out every widget it can lay out
   /// except the [FloatingActionButton]. The [Scaffold] uses the [Offset]
@@ -130,8 +154,70 @@ class _EndFloatFabLocation extends FloatingActionButtonLocation {
   }
 }
 
+// Provider of common logic for [FloatingActionButtonLocation]s that
+// dock to the [BottomAppBar].
+abstract class _DockedFloatingActionButtonLocation extends FloatingActionButtonLocation {
+  const _DockedFloatingActionButtonLocation();
+
+  // Positions the Y coordinate of the [FloatingActionButton] at a height
+  // where it docks to the [BottomAppBar].
+  @protected
+  double getDockedY(ScaffoldPrelayoutGeometry scaffoldGeometry) {
+    final double contentBottom = scaffoldGeometry.contentBottom;
+    final double bottomSheetHeight = scaffoldGeometry.bottomSheetSize.height;
+    final double fabHeight = scaffoldGeometry.floatingActionButtonSize.height;
+    final double snackBarHeight = scaffoldGeometry.snackBarSize.height;
+
+    double fabY = contentBottom - fabHeight / 2.0;
+    // The FAB should sit with a margin between it and the snack bar.
+    if (snackBarHeight > 0.0)
+      fabY = math.min(fabY, contentBottom - snackBarHeight - fabHeight - kFloatingActionButtonMargin);
+    // The FAB should sit with its center in front of the top of the bottom sheet.
+    if (bottomSheetHeight > 0.0)
+      fabY = math.min(fabY, contentBottom - bottomSheetHeight - fabHeight / 2.0);
+
+    final double maxFabY = scaffoldGeometry.scaffoldSize.height - fabHeight;
+    return math.min(maxFabY, fabY);
+  }
+}
+
+class _EndDockedFloatingActionButtonLocation extends _DockedFloatingActionButtonLocation {
+  const _EndDockedFloatingActionButtonLocation();
+
+  @override
+  Offset getOffset(ScaffoldPrelayoutGeometry scaffoldGeometry) {
+    // Compute the x-axis offset.
+    double fabX;
+    assert(scaffoldGeometry.textDirection != null);
+    switch (scaffoldGeometry.textDirection) {
+      case TextDirection.rtl:
+        // In RTL, the end of the screen is the left.
+        final double endPadding = scaffoldGeometry.minInsets.left;
+        fabX = kFloatingActionButtonMargin + endPadding;
+        break;
+      case TextDirection.ltr:
+        // In LTR, the end of the screen is the right.
+        final double endPadding = scaffoldGeometry.minInsets.right;
+        fabX = scaffoldGeometry.scaffoldSize.width - scaffoldGeometry.floatingActionButtonSize.width - kFloatingActionButtonMargin - endPadding;
+      break;
+    }
+    // Return an offset with a docked Y coordinate.
+    return new Offset(fabX, getDockedY(scaffoldGeometry));
+  }
+}
+
+class _CenterDockedFloatingActionButtonLocation extends _DockedFloatingActionButtonLocation {
+  const _CenterDockedFloatingActionButtonLocation();
+
+  @override
+  Offset getOffset(ScaffoldPrelayoutGeometry scaffoldGeometry) {
+    final double fabX = (scaffoldGeometry.scaffoldSize.width - scaffoldGeometry.floatingActionButtonSize.width) / 2.0;
+    return new Offset(fabX, getDockedY(scaffoldGeometry));
+  }
+}
+
 /// Provider of animations to move the [FloatingActionButton] between [FloatingActionButtonLocation]s.
-/// 
+///
 /// The [Scaffold] uses [Scaffold.floatingActionButtonAnimator] to define:
 ///
 ///  * The [Offset] of the [FloatingActionButton] between the old and new
@@ -139,48 +225,48 @@ class _EndFloatFabLocation extends FloatingActionButtonLocation {
 ///  * An [Animation] to scale the [FloatingActionButton] during the transition.
 ///  * An [Animation] to rotate the [FloatingActionButton] during the transition.
 ///  * Where to start a new animation from if an animation is interrupted.
-/// 
+///
 /// See also:
-/// 
+///
 ///  * [FloatingActionButton], which is a circular button typically shown in the
 ///    bottom right corner of the app.
-///  * [FloatingActionButtonLocation], which the [Scaffold] uses to place the 
-///    [Scaffold.floatingActionButton] within the [Scaffold]'s layout. 
+///  * [FloatingActionButtonLocation], which the [Scaffold] uses to place the
+///    [Scaffold.floatingActionButton] within the [Scaffold]'s layout.
 abstract class FloatingActionButtonAnimator {
   /// Abstract const constructor. This constructor enables subclasses to provide
   /// const constructors so that they can be used in const expressions.
   const FloatingActionButtonAnimator();
 
-  /// Moves the [FloatingActionButton] by scaling out and then in at a new 
+  /// Moves the [FloatingActionButton] by scaling out and then in at a new
   /// [FloatingActionButtonLocation].
-  /// 
+  ///
   /// This animator shrinks the [FloatingActionButton] down until it disappears, then
   /// grows it back to full size at its new [FloatingActionButtonLocation].
-  /// 
+  ///
   /// This is the default [FloatingActionButton] motion animation.
   static const FloatingActionButtonAnimator scaling = const _ScalingFabMotionAnimator();
 
   /// Gets the [FloatingActionButton]'s position relative to the origin of the
   /// [Scaffold] based on [progress].
-  /// 
-  /// [begin] is the [Offset] provided by the previous 
+  ///
+  /// [begin] is the [Offset] provided by the previous
   /// [FloatingActionButtonLocation].
-  /// 
-  /// [end] is the [Offset] provided by the new 
+  ///
+  /// [end] is the [Offset] provided by the new
   /// [FloatingActionButtonLocation].
-  /// 
+  ///
   /// [progress] is the current progress of the transition animation.
   /// When [progress] is 0.0, the returned [Offset] should be equal to [begin].
   /// when [progress] is 1.0, the returned [Offset] should be equal to [end].
   Offset getOffset({@required Offset begin, @required Offset end, @required double progress});
 
   /// Animates the scale of the [FloatingActionButton].
-  /// 
+  ///
   /// The animation should both start and end with a value of 1.0.
-  /// 
+  ///
   /// For example, to create an animation that linearly scales out and then back in,
   /// you could join animations that pass each other:
-  /// 
+  ///
   /// ```dart
   ///   @override
   ///   Animation<double> getScaleAnimation({@required Animation<double> parent}) {
@@ -194,15 +280,15 @@ abstract class FloatingActionButtonAnimator {
   Animation<double> getScaleAnimation({@required Animation<double> parent});
 
   /// Animates the rotation of [Scaffold.floatingActionButton].
-  /// 
+  ///
   /// The animation should both start and end with a value of 0.0 or 1.0.
-  /// 
+  ///
   /// The animation values are a fraction of a full circle, with 0.0 and 1.0
   /// corresponding to 0 and 360 degrees, while 0.5 corresponds to 180 degrees.
-  /// 
-  /// For example, to create a rotation animation that rotates the 
+  ///
+  /// For example, to create a rotation animation that rotates the
   /// [FloatingActionButton] through a full circle:
-  /// 
+  ///
   /// ```dart
   ///   @override
   ///   Animation<double> getRotationAnimation({@required Animation<double> parent}) {
@@ -212,15 +298,15 @@ abstract class FloatingActionButtonAnimator {
   Animation<double> getRotationAnimation({@required Animation<double> parent});
 
   /// Gets the progress value to restart a motion animation from when the animation is interrupted.
-  /// 
+  ///
   /// [previousValue] is the value of the animation before it was interrupted.
-  /// 
+  ///
   /// The restart of the animation will affect all three parts of the motion animation:
   /// offset animation, scale animation, and rotation animation.
-  /// 
+  ///
   /// An interruption triggers if the [Scaffold] is given a new [FloatingActionButtonLocation]
   /// while it is still animating a transition between two previous [FloatingActionButtonLocation]s.
-  /// 
+  ///
   /// A sensible default is usually 0.0, which is the same as restarting
   /// the animation from the beginning, regardless of the original state of the animation.
   double getAnimationRestart(double previousValue) => 0.0;
@@ -256,10 +342,10 @@ class _ScalingFabMotionAnimator extends FloatingActionButtonAnimator {
 
   @override
   Animation<double> getRotationAnimation({Animation<double> parent}) {
-    // Because we only see the last half of the rotation tween, 
+    // Because we only see the last half of the rotation tween,
     // it needs to go twice as far.
     final Tween<double> rotationTween = new Tween<double>(
-      begin: 1.0 - kFloatingActionButtonTurnInterval * 2, 
+      begin: 1.0 - kFloatingActionButtonTurnInterval * 2,
       end: 1.0,
     );
     // This rotation will turn on the way in, but not on the way out.
@@ -294,4 +380,4 @@ class _AnimationSwap<T> extends CompoundAnimation<T> {
 
   @override
   T get value => parent.value < swapThreshold ? first.value : next.value;
-}
\ No newline at end of file
+}

packages/flutter/test/material/floating_action_button_location_test.dart

@@ -7,53 +7,31 @@ import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  group('Floating action button positioner', () {
-    Widget build(FloatingActionButton fab, FloatingActionButtonLocation fabLocation, [_GeometryListener listener]) {
-      return new Directionality(
-        textDirection: TextDirection.ltr,
-        child: new MediaQuery(
-          data: const MediaQueryData(
-            viewInsets: const EdgeInsets.only(bottom: 200.0),
-          ),
-          child: new Scaffold(
-            appBar: new AppBar(title: const Text('FabLocation Test')),
-            floatingActionButtonLocation: fabLocation,
-            floatingActionButton: fab,
-            body: listener,
-          ),
-        ),
-      );
-    }
-
-    const FloatingActionButton fab1 = const FloatingActionButton(
-        onPressed: null,
-        child: const Text('1'),
-      );
-
+  group('Basic floating action button locations', () {
     testWidgets('still animates motion when the floating action button is null', (WidgetTester tester) async {
-      await tester.pumpWidget(build(null, null));
+      await tester.pumpWidget(buildFrame(fab: null, location: null));
 
       expect(find.byType(FloatingActionButton), findsNothing);
       expect(tester.binding.transientCallbackCount, 0);
 
-      await tester.pumpWidget(build(null, FloatingActionButtonLocation.endFloat));
+      await tester.pumpWidget(buildFrame(fab: null, location: FloatingActionButtonLocation.endFloat));
 
       expect(find.byType(FloatingActionButton), findsNothing);
       expect(tester.binding.transientCallbackCount, greaterThan(0));
 
-      await tester.pumpWidget(build(null, FloatingActionButtonLocation.centerFloat));
+      await tester.pumpWidget(buildFrame(fab: null, location: FloatingActionButtonLocation.centerFloat));
 
       expect(find.byType(FloatingActionButton), findsNothing);
       expect(tester.binding.transientCallbackCount, greaterThan(0));
     });
 
     testWidgets('moves fab from center to end and back', (WidgetTester tester) async {
-      await tester.pumpWidget(build(fab1, FloatingActionButtonLocation.endFloat));
+      await tester.pumpWidget(buildFrame(location: FloatingActionButtonLocation.endFloat));
 
       expect(tester.getCenter(find.byType(FloatingActionButton)), const Offset(756.0, 356.0));
       expect(tester.binding.transientCallbackCount, 0);
 
-      await tester.pumpWidget(build(fab1, FloatingActionButtonLocation.centerFloat));
+      await tester.pumpWidget(buildFrame(location: FloatingActionButtonLocation.centerFloat));
 
       expect(tester.binding.transientCallbackCount, greaterThan(0));
 
@@ -62,8 +40,8 @@ void main() {
       expect(tester.getCenter(find.byType(FloatingActionButton)), const Offset(400.0, 356.0));
       expect(tester.binding.transientCallbackCount, 0);
 
-      await tester.pumpWidget(build(fab1, FloatingActionButtonLocation.endFloat));
-      
+      await tester.pumpWidget(buildFrame(location: FloatingActionButtonLocation.endFloat));
+
       expect(tester.binding.transientCallbackCount, greaterThan(0));
 
       await tester.pumpAndSettle();
@@ -73,11 +51,11 @@ void main() {
     });
 
     testWidgets('moves to and from custom-defined positions', (WidgetTester tester) async {
-      await tester.pumpWidget(build(fab1, _kTopStartFabLocation));
+      await tester.pumpWidget(buildFrame(location: const _StartTopFloatingActionButtonLocation()));
 
       expect(tester.getCenter(find.byType(FloatingActionButton)), const Offset(44.0, 56.0));
 
-      await tester.pumpWidget(build(fab1, FloatingActionButtonLocation.centerFloat));
+      await tester.pumpWidget(buildFrame(location: FloatingActionButtonLocation.centerFloat));
       expect(tester.binding.transientCallbackCount, greaterThan(0));
 
       await tester.pumpAndSettle();
@@ -85,8 +63,8 @@ void main() {
       expect(tester.getCenter(find.byType(FloatingActionButton)), const Offset(400.0, 356.0));
       expect(tester.binding.transientCallbackCount, 0);
 
-      await tester.pumpWidget(build(fab1, _kTopStartFabLocation));
-      
+      await tester.pumpWidget(buildFrame(location: const _StartTopFloatingActionButtonLocation()));
+
       expect(tester.binding.transientCallbackCount, greaterThan(0));
 
       await tester.pumpAndSettle();
@@ -122,23 +100,76 @@ void main() {
 
       // We'll listen to the Scaffold's geometry for any 'jumps' to a size of 1 to detect changes in the size and rotation of the fab.
       // Creating a scaffold with the fab at endFloat
-      await tester.pumpWidget(build(fab1, FloatingActionButtonLocation.endFloat, geometryListener));
-      
+      await tester.pumpWidget(buildFrame(location: FloatingActionButtonLocation.endFloat, listener: geometryListener));
+
       listenerState = tester.state(find.byType(_GeometryListener));
       listenerState.geometryListenable.addListener(check);
-      
+
       // Moving the fab to centerFloat'
-      await tester.pumpWidget(build(fab1, FloatingActionButtonLocation.centerFloat, geometryListener));
+      await tester.pumpWidget(buildFrame(location: FloatingActionButtonLocation.centerFloat, listener: geometryListener));
       await tester.pumpAndSettle();
 
       // Moving the fab to the top start after finishing the previous motion
-      await tester.pumpWidget(build(fab1, _kTopStartFabLocation, geometryListener));
+      await tester.pumpWidget(buildFrame(location: const _StartTopFloatingActionButtonLocation(), listener: geometryListener));
 
       // Interrupting motion to move to the end float
-      await tester.pumpWidget(build(fab1, FloatingActionButtonLocation.endFloat, geometryListener));
+      await tester.pumpWidget(buildFrame(location: FloatingActionButtonLocation.endFloat, listener: geometryListener));
       await tester.pumpAndSettle();
     });
+  });
+
+  testWidgets('Docked floating action button locations', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      buildFrame(
+        location: FloatingActionButtonLocation.endDocked,
+        bab: const SizedBox(height: 100.0),
+        viewInsets: EdgeInsets.zero,
+      ),
+    );
+
+    // Scaffold 800x600, FAB is 56x56, BAB is 800x100, FAB's center is
+    // at the top of the BAB.
+    expect(tester.getCenter(find.byType(FloatingActionButton)), const Offset(756.0, 500.0));
 
+    await tester.pumpWidget(
+      buildFrame(
+        location: FloatingActionButtonLocation.centerDocked,
+        bab: const SizedBox(height: 100.0),
+        viewInsets: EdgeInsets.zero,
+      ),
+    );
+    await tester.pumpAndSettle();
+    expect(tester.getCenter(find.byType(FloatingActionButton)), const Offset(400.0, 500.0));
+
+
+    await tester.pumpWidget(
+      buildFrame(
+        location: FloatingActionButtonLocation.endDocked,
+        bab: const SizedBox(height: 100.0),
+        viewInsets: EdgeInsets.zero,
+      ),
+    );
+    await tester.pumpAndSettle();
+    expect(tester.getCenter(find.byType(FloatingActionButton)), const Offset(756.0, 500.0));
+  });
+
+  testWidgets('Docked floating action button locations: no BAB, small BAB', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      buildFrame(
+        location: FloatingActionButtonLocation.endDocked,
+        viewInsets: EdgeInsets.zero,
+      ),
+    );
+    expect(tester.getCenter(find.byType(FloatingActionButton)), const Offset(756.0, 572.0));
+
+    await tester.pumpWidget(
+      buildFrame(
+        location: FloatingActionButtonLocation.endDocked,
+        bab: const SizedBox(height: 16.0),
+        viewInsets: EdgeInsets.zero,
+      ),
+    );
+    expect(tester.getCenter(find.byType(FloatingActionButton)), const Offset(756.0, 572.0));
   });
 }
 
@@ -169,7 +200,7 @@ class _GeometryListenerState extends State<_GeometryListener> {
 
     if (geometryListenable != null)
       geometryListenable.removeListener(onGeometryChanged);
-    
+
     geometryListenable = newListenable;
     geometryListenable.addListener(onGeometryChanged);
     cache = new _GeometryCachePainter(geometryListenable);
@@ -201,15 +232,50 @@ class _GeometryCachePainter extends CustomPainter {
   }
 }
 
-const _TopStartFabLocation _kTopStartFabLocation = const _TopStartFabLocation();
+Widget buildFrame({
+  FloatingActionButton fab: const FloatingActionButton(
+    onPressed: null,
+    child: const Text('1'),
+  ),
+  FloatingActionButtonLocation location,
+  _GeometryListener listener,
+  TextDirection textDirection: TextDirection.ltr,
+  EdgeInsets viewInsets: const EdgeInsets.only(bottom: 200.0),
+  Widget bab,
+}) {
+  return new Directionality(
+    textDirection: textDirection,
+    child: new MediaQuery(
+      data: new MediaQueryData(viewInsets: viewInsets),
+      child: new Scaffold(
+        appBar: new AppBar(title: const Text('FabLocation Test')),
+        floatingActionButtonLocation: location,
+        floatingActionButton: fab,
+        bottomNavigationBar: bab,
+        body: listener,
+      ),
+    ),
+  );
+}
 
-class _TopStartFabLocation extends FloatingActionButtonLocation {
-  const _TopStartFabLocation();
+class _StartTopFloatingActionButtonLocation extends FloatingActionButtonLocation {
+  const _StartTopFloatingActionButtonLocation();
 
   @override
   Offset getOffset(ScaffoldPrelayoutGeometry scaffoldGeometry) {
-    final double fabX = 16.0 + scaffoldGeometry.minInsets.left;
+    double fabX;
+    assert(scaffoldGeometry.textDirection != null);
+    switch (scaffoldGeometry.textDirection) {
+      case TextDirection.rtl:
+        final double startPadding = kFloatingActionButtonMargin + scaffoldGeometry.minInsets.right;
+        fabX = scaffoldGeometry.scaffoldSize.width - scaffoldGeometry.floatingActionButtonSize.width - startPadding;
+        break;
+      case TextDirection.ltr:
+        final double startPadding = kFloatingActionButtonMargin + scaffoldGeometry.minInsets.left;
+        fabX = startPadding;
+        break;
+    }
     final double fabY = scaffoldGeometry.contentTop - (scaffoldGeometry.floatingActionButtonSize.height / 2.0);
     return new Offset(fabX, fabY);
   }
-}
\ No newline at end of file
+}