GestureTapDownCallback typedef Null safety
Signature for when a pointer that might cause a tap has contacted the screen.
The position at which the pointer contacted the screen is available in the
- GestureDetector.onTapDown, which matches this signature.
- TapGestureRecognizer, which uses this signature in one of its callbacks.
typedef GestureTapDownCallback = void Function(TapDownDetails details);