Haptic feedback on time changes in TimePicker (#8348)

Trigger a vibration on hour/minute changes, with an upper bound on
number of feedback events per second.

Note: state changes are expected to trigger haptic feedback on Android,
but not on iOS time pickers.

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

@@ -22,6 +22,7 @@ const double _kTwoPi = 2 * math.PI;
 const int _kHoursPerDay = 24;
 const int _kHoursPerPeriod = 12;
 const int _kMinutesPerHour = 60;
+const Duration _kVibrateCommitDelay = const Duration(milliseconds: 100);
 
 /// Whether the [TimeOfDay] is before or after noon.
 enum DayPeriod {
@@ -644,12 +645,17 @@ class _TimePickerDialogState extends State<_TimePickerDialog> {
 
   _TimePickerMode _mode = _TimePickerMode.hour;
   TimeOfDay _selectedTime;
+  Timer _vibrateTimer;
 
   void _vibrate() {
     switch (Theme.of(context).platform) {
       case TargetPlatform.android:
       case TargetPlatform.fuchsia:
-        HapticFeedback.vibrate();
+        _vibrateTimer?.cancel();
+        _vibrateTimer = new Timer(_kVibrateCommitDelay, () {
+          HapticFeedback.vibrate();
+          _vibrateTimer = null;
+        });
         break;
       case TargetPlatform.iOS:
         break;
@@ -664,6 +670,7 @@ class _TimePickerDialogState extends State<_TimePickerDialog> {
   }
 
   void _handleTimeChanged(TimeOfDay value) {
+    _vibrate();
     setState(() {
       _selectedTime = value;
     });
@@ -759,6 +766,13 @@ class _TimePickerDialogState extends State<_TimePickerDialog> {
       )
     );
   }
+
+  @override
+  void dispose() {
+    _vibrateTimer?.cancel();
+    _vibrateTimer = null;
+    super.dispose();
+  }
 }
 
 /// Shows a dialog containing a material design time picker.

packages/flutter/test/material/time_picker_test.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 class _TimePickerLauncher extends StatelessWidget {
@@ -110,4 +111,92 @@ void main() {
     await finishPicker(tester);
     expect(result.hour, equals(9));
   });
+
+  group('haptic feedback', () {
+    const Duration kFastFeedbackInteral = const Duration(milliseconds: 10);
+    const Duration kSlowFeedbackInteral = const Duration(milliseconds: 200);
+    int hapticFeedbackCount;
+
+    setUpAll(() {
+      PlatformMessages.setMockJSONMessageHandler('flutter/platform', (dynamic message) {
+        if (message['method'] == "HapticFeedback.vibrate")
+          hapticFeedbackCount++;
+      });
+    });
+
+    setUp(() {
+      hapticFeedbackCount = 0;
+    });
+
+    testWidgets('tap-select vibrates once', (WidgetTester tester) async {
+      Point center = await startPicker(tester, (TimeOfDay time) { });
+      await tester.tapAt(new Point(center.x, center.y - 50.0));
+      await finishPicker(tester);
+      expect(hapticFeedbackCount, 1);
+    });
+
+    testWidgets('quick successive tap-selects vibrate once', (WidgetTester tester) async {
+      Point center = await startPicker(tester, (TimeOfDay time) { });
+      await tester.tapAt(new Point(center.x, center.y - 50.0));
+      await tester.pump(kFastFeedbackInteral);
+      await tester.tapAt(new Point(center.x, center.y + 50.0));
+      await finishPicker(tester);
+      expect(hapticFeedbackCount, 1);
+    });
+
+    testWidgets('slow successive tap-selects vibrate once per tap', (WidgetTester tester) async {
+      Point center = await startPicker(tester, (TimeOfDay time) { });
+      await tester.tapAt(new Point(center.x, center.y - 50.0));
+      await tester.pump(kSlowFeedbackInteral);
+      await tester.tapAt(new Point(center.x, center.y + 50.0));
+      await tester.pump(kSlowFeedbackInteral);
+      await tester.tapAt(new Point(center.x, center.y - 50.0));
+      await finishPicker(tester);
+      expect(hapticFeedbackCount, 3);
+    });
+
+    testWidgets('drag-select vibrates once', (WidgetTester tester) async {
+      Point center = await startPicker(tester, (TimeOfDay time) { });
+      Point hour0 = new Point(center.x, center.y - 50.0);
+      Point hour3 = new Point(center.x + 50.0, center.y);
+
+      TestGesture gesture = await tester.startGesture(hour3);
+      await gesture.moveBy(hour0 - hour3);
+      await gesture.up();
+      await finishPicker(tester);
+      expect(hapticFeedbackCount, 1);
+    });
+
+    testWidgets('quick drag-select vibrates once', (WidgetTester tester) async {
+      Point center = await startPicker(tester, (TimeOfDay time) { });
+      Point hour0 = new Point(center.x, center.y - 50.0);
+      Point hour3 = new Point(center.x + 50.0, center.y);
+
+      TestGesture gesture = await tester.startGesture(hour3);
+      await gesture.moveBy(hour0 - hour3);
+      await tester.pump(kFastFeedbackInteral);
+      await gesture.moveBy(hour3 - hour0);
+      await tester.pump(kFastFeedbackInteral);
+      await gesture.moveBy(hour0 - hour3);
+      await gesture.up();
+      await finishPicker(tester);
+      expect(hapticFeedbackCount, 1);
+    });
+
+    testWidgets('slow drag-select vibrates once', (WidgetTester tester) async {
+      Point center = await startPicker(tester, (TimeOfDay time) { });
+      Point hour0 = new Point(center.x, center.y - 50.0);
+      Point hour3 = new Point(center.x + 50.0, center.y);
+
+      TestGesture gesture = await tester.startGesture(hour3);
+      await gesture.moveBy(hour0 - hour3);
+      await tester.pump(kSlowFeedbackInteral);
+      await gesture.moveBy(hour3 - hour0);
+      await tester.pump(kSlowFeedbackInteral);
+      await gesture.moveBy(hour0 - hour3);
+      await gesture.up();
+      await finishPicker(tester);
+      expect(hapticFeedbackCount, 3);
+    });
+  });
 }