dispose method

@override @mustCallSuper void dispose()

Dipsoses this ValueListenable and sets isDisposed to true. Successive calls to this method will be ignored.

Implementation

@override
@mustCallSuper
void dispose() {
  if (!_isDisposed) {
    super.dispose();
    this._isDisposed = true;
  } else {
    // todo: Log warning!
  }
}