detach method
Implementation
void detach(ScrollPosition position) {
assert(_positionToListener.containsKey(position));
_positionToListener[position]!.forceCancel();
_positionToListener.remove(position);
}
void detach(ScrollPosition position) {
assert(_positionToListener.containsKey(position));
_positionToListener[position]!.forceCancel();
_positionToListener.remove(position);
}