Flutter判断context!=null还是mount

abstract class State {
  bool get mounted => _element != null;
  
  BuildContext get context {
    return _element!;
  }
}

abstract class Element {
  void unmount() {
    _widget = null;
    _dependencies = null;
    _lifecycleState = _ElementLifecycle.defunct;
  }
}

所以判断context!=null和mount，是等效的。