1. protected
MultiDragGestureRecognizer<MultiDragPointerState> 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 

@protected
MultiDragGestureRecognizer<MultiDragPointerState> createRecognizer(GestureMultiDragStartCallback onStart) {
  switch (affinity) {
    case Axis.horizontal:
      return new HorizontalMultiDragGestureRecognizer()..onStart = onStart;
    case Axis.vertical:
      return new VerticalMultiDragGestureRecognizer()..onStart = onStart;
  }
  return new ImmediateMultiDragGestureRecognizer()..onStart = onStart;
}