1. override
void dispose()

Releases any resources used by the object.

This method is called by the owner of this gesture recognizer when the object is no longer needed (e.g. when a gesture recognizer is being unregistered from a GestureDetector, the GestureDetector widget calls this method).

Source 

@override
void dispose() {
  resolve(GestureDisposition.rejected);
  for (int pointer in _trackedPointers)
    GestureBinding.instance.pointerRouter.removeRoute(pointer, handleEvent);
  _trackedPointers.clear();
  assert(_entries.isEmpty);
  super.dispose();
}