1. override
void rejectGesture(int pointer)

Called when this member loses the arena for the given pointer id.

Source 

@override
void rejectGesture(int pointer) {
  assert(_pointers != null);
  if (_pointers.containsKey(pointer)) {
    T state = _pointers[pointer];
    assert(state != null);
    state.rejected();
    _removeState(pointer);
  } // else we already preemptively forgot about it (e.g. we got an up event)
}