Data not rebuild (restart) with rxdart

Question

I do floating alert which is controlled with stream. The logic of that alert is, when tap the OK button on it to turn true to stream and then close.

I will show my codes, and please fix me what my logic wrong.

 Widget dataState(
      AsyncSnapshot pinValidateSnapshot, ChangePinBloc changePinBloc) {
    if (pinValidateSnapshot.data == true) {
      WidgetsBinding.instance.addPostFrameCallback(
          (_) => Navigator.pushNamed(context, newConfirmPinRoute));
    }
    else if(pinValidateSnapshot.data == false){
      return StreamBuilder(
        stream: changePinBloc.alertStream,
        builder: (context, AsyncSnapshot<bool> alertSnapshot) {
          // if (alertSnapshot.hasError) {
          //   changePinBloc.onCloseAlert(false);
          // }
          return Positioned.fill(
            child: Visibility(
              visible: alertSnapshot.data != true,
              child: AlertContainerView(
                message: 'Same',
                onOKTap: () {
                  changePinBloc.onCloseAlert(true);
                },
              ),
            ),
          );
        },
      );
    }
    return Center(child: Text('WTF'),);
  }

Here is codes in bloc class

final alertController = PublishSubject<bool>();
Stream<bool>get alertStream => alertController.stream;

  void onCloseAlert(bool flag) {
    alertController.sink.add(flag);

  }

In here although pinValidateSnapshot change state, the alertSnapshot don't change start again from initial state, it always left previous state and alert not show again. How to do with that?