1. override
DelayedMultiDragGestureRecognizer createRecognizer(GestureMultiDragStartCallback onStart)

Creates a gesture recognizer that recognizes the start of the drag.

Subclasses can override this function to customize when they start recognizing a drag.

Source 

@override
DelayedMultiDragGestureRecognizer createRecognizer(GestureMultiDragStartCallback onStart) {
  return new DelayedMultiDragGestureRecognizer()
    ..onStart = (Point position) {
      Drag result = onStart(position);
      if (result != null)
        HapticFeedback.vibrate();
      return result;
    };
}