Navigate based on data from stream

Question

Stream builder is used to draw widget based on data from stream.

What is the right way to achieve navigation based on the data?

Details: There is a logout button in drawer. It clears the session and emits a data in the stream.

There's a stateless widget with stream builder listening on data and updating UI. How to make it navigate to login screen based on data in the stream?

Possible duplicate of [Navigating to a new screen when stream value in BLOC changes](https://stackoverflow.com/questions/54101589/navigating-to-a-new-screen-when-stream-value-in-bloc-changes) — mirkancal, May 05 '19 at 13:38

score -1 · Answer 1 · answered May 05 '19 at 10:38

-1

In your stateless widget's build method, you can listen changes in your stream with listen() method.

 Widget build(BuildContext context) {
    Repository.bulletins.listen((pet) {
      pet.documents[pet.documents.length - 1].data['animalType'] == "Dog"
          ? Navigator.push(
              context,
              MaterialPageRoute(
                builder: (context) => LostPetForm(),
              ))
          : print('not yet');
    });
    return Scaffold(...

answered May 05 '19 at 10:38

mirkancal

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```I/flutter (14304): The following assertion was thrown while finalizing the widget tree: I/flutter (14304): setState() or markNeedsBuild() called when widget tree was locked. I/flutter (14304): This _ModalScope widget cannot be marked as needing to build because the framework is I/flutter (14304): locked.``` I get this exception when I navigated from listener method inside build method. I read it is not possible to navigate from inside build method. – Harish Reddy May 05 '19 at 12:53
Where did you read it? I've post it after I've tried on a small app with 2 screens and firestore on the backend, it navigated itself when I changed the data from Firestore, without a problem. This error means that you are calling setState during the build phase. If you didn't use setState, Navigator.pop uses setState internally according to this SO post. https://stackoverflow.com/a/51246379/9779791 Maybe you can try using Navigator somewhere else in the code, maybe in initState() – mirkancal May 05 '19 at 13:33

score -1 · Answer 2 · answered May 05 '19 at 13:25

Inspired from https://stackoverflow.com/a/54109955/1918649

In the build method of the widget that creates Profile

  @override
  Widget build(BuildContext context) {
    final userBloc = BlocProvider.of<UserBloc>(context);
    return ...
           somewhere here Profile(userBloc)
           ...
}

class Profile extends StatefulWidget  {

  final userBloc;

  Profile(this.userBloc);

  @override
  State<StatefulWidget> createState() => ProfileState();
}

class ProfileState extends State<Profile> {

  @override
  void initState() {
    super.initState();
    widget.userBloc.stream.listen((userData){
      if(userData==null) {
        Navigator.push(
            context,
            MaterialPageRoute(
              builder: (context) => LandingPage(),
            ));
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: new AppBar(
        title: new Text("Profile"),
      ),
      drawer: CustomDrawer(),
      body: Center(
        child: StreamBuilder<UserModel>(
          initialData: widget.userBloc.user,
          stream: widget.userBloc.stream,
          builder: (ctx, snap) => snap.hasData?Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Image.network(snap.data?.imageUrl),
              Text(snap.data?.username)
            ],
          ):Text('You are logged out'),
        ),
      ),
    );
  }
}

Navigate based on data from stream

2 Answers2