dispose method

  1. @mustCallSuper
void dispose ()
@mustCallSuper

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 

@mustCallSuper
void dispose() {
  assert(_debugAssertNotDisposed());
  _listeners = null;
}