onLongPressStart property Null safety
Called when a long press gesture with a primary button has been recognized.
Triggered when a pointer has remained in contact with the screen at the same location for a long period of time.
This is equivalent to (and is called immediately before) onLongPress. The only difference between the two is that this callback contains details of the position at which the pointer initially contacted the screen, whereas onLongPress does not.
final GestureLongPressStartCallback? onLongPressStart;