GestureDragUpdateCallback typedef

void GestureDragUpdateCallback (DragUpdateDetails details)

Signature for when a pointer that is in contact with the screen and moving has moved again.

The details object provides the position of the touch and the distance it has travelled since the last update.

See DragGestureRecognizer.onUpdate.

Implementation 

typedef GestureDragUpdateCallback = void Function(DragUpdateDetails details);