Called when a long press gesture with a secondary 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) onSecondaryLongPress. The only difference between the two is that this callback contains details of the position at which the pointer initially contacted the screen, whereas onSecondaryLongPress does not.
- kSecondaryButton, the button this callback responds to.
- LongPressGestureRecognizer.onSecondaryLongPressStart, which exposes this callback at the gesture layer.
final GestureLongPressStartCallback? onSecondaryLongPressStart;