dispose method

  1. @override
void dispose ()
override

Discards any resources used by the object. After this is called, the object is not in a usable state and should be discarded (calls to addListener and removeListener will throw after the object is disposed).

This method should only be called by the object's owner.

Implementation 

@override
void dispose() {
  for (ScrollPosition position in positions) {
    assert(_positionToListener.containsKey(position));
    position.removeListener(_positionToListener[position]);
  }
  super.dispose();
}