Add optional haptic feedback on LongPressDraggable (#18781)

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

@@ -267,6 +267,7 @@ class LongPressDraggable<T> extends Draggable<T> {
     VoidCallback onDragStarted,
     DraggableCanceledCallback onDraggableCanceled,
     VoidCallback onDragCompleted,
+    this.hapticFeedbackOnStart = true,
     bool ignoringFeedbackSemantics = true,
   }) : super(
     key: key,
@@ -284,12 +285,15 @@ class LongPressDraggable<T> extends Draggable<T> {
     ignoringFeedbackSemantics: ignoringFeedbackSemantics,
   );
 
+  /// Whether haptic feedback should be triggered on drag start.
+  final bool hapticFeedbackOnStart;
+
   @override
   DelayedMultiDragGestureRecognizer createRecognizer(GestureMultiDragStartCallback onStart) {
     return new DelayedMultiDragGestureRecognizer()
       ..onStart = (Offset position) {
         final Drag result = onStart(position);
-        if (result != null)
+        if (result != null && hapticFeedbackOnStart)
           HapticFeedback.vibrate();
         return result;
       };

packages/flutter/test/widgets/draggable_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter/semantics.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/services.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/gestures.dart';
 
@@ -1635,6 +1636,14 @@ void main() {
     expect(onDragStartedCalled, isTrue);
   });
 
+  testWidgets('long-press draggable calls Haptic Feedback onStart', (WidgetTester tester) async {
+    await _testLongPressDraggableHapticFeedback(tester: tester, hapticFeedbackOnStart: true, expectedHapticFeedbackCount: 1);
+  });
+
+  testWidgets('long-press draggable can disable Haptic Feedback', (WidgetTester tester) async {
+    await _testLongPressDraggableHapticFeedback(tester: tester, hapticFeedbackOnStart: false, expectedHapticFeedbackCount: 0);
+  });
+
   testWidgets('Drag feedback with child anchor positions correctly', (WidgetTester tester) async {
     await _testChildAnchorFeedbackPosition(tester: tester);
   });
@@ -1793,6 +1802,48 @@ void main() {
 
 }
 
+Future<Null> _testLongPressDraggableHapticFeedback({WidgetTester tester, bool hapticFeedbackOnStart, int expectedHapticFeedbackCount}) async {
+  bool onDragStartedCalled = false;
+
+  int hapticFeedbackCalls = 0;
+  SystemChannels.platform.setMockMethodCallHandler((MethodCall methodCall) async {
+    if (methodCall.method == 'HapticFeedback.vibrate') {
+      hapticFeedbackCalls++;
+    }
+  });
+
+  await tester.pumpWidget(new MaterialApp(
+    home: new LongPressDraggable<int>(
+      data: 1,
+      child: const Text('Source'),
+      feedback: const Text('Dragging'),
+      hapticFeedbackOnStart: hapticFeedbackOnStart,
+      onDragStarted: () {
+        onDragStartedCalled = true;
+      },
+    ),
+  ));
+
+  expect(find.text('Source'), findsOneWidget);
+  expect(find.text('Dragging'), findsNothing);
+  expect(onDragStartedCalled, isFalse);
+
+  final Offset firstLocation = tester.getCenter(find.text('Source'));
+  await tester.startGesture(firstLocation, pointer: 7);
+  await tester.pump();
+
+  expect(find.text('Source'), findsOneWidget);
+  expect(find.text('Dragging'), findsNothing);
+  expect(onDragStartedCalled, isFalse);
+
+  await tester.pump(kLongPressTimeout);
+
+  expect(find.text('Source'), findsOneWidget);
+  expect(find.text('Dragging'), findsOneWidget);
+  expect(onDragStartedCalled, isTrue);
+  expect(hapticFeedbackCalls, expectedHapticFeedbackCount);
+}
+
 Future<Null> _testChildAnchorFeedbackPosition({WidgetTester tester, double top = 0.0, double left = 0.0}) async {
   final List<int> accepted = <int>[];
   int dragStartedCount = 0;