Flutter show SnackBar and return empty Container in StreamBuilder throws an Error

Question

Hello I am trying to show Snackbar if network response return error right now My Build function looks like this:

  @override
  Widget build(BuildContext context) {
    NewsBloc bloc = NewsBloc();
    return Scaffold(
      key: scaffoldKey,
      body: Container(
        color: Colors.white,
        child: StreamBuilder<List<BaseModel>>(
          stream: bloc.newsStream,
          builder: (BuildContext context, AsyncSnapshot<List<BaseModel>> snap) {
            if (snap.hasError) {
              scaffoldKey.currentState.showSnackBar(SnackBar(
                content: Container(
                  height: 100,
                ),
              ));
              return Center(child: Text(snap.error));
            } else if (!snap.hasData) {
              return Center(child: CircularProgressIndicator());
            } else {
              return _newsList(snap.data);
            }
          },
        ),
      ),
    );
  }

It shows the Snackbar but also throws an error:

This Scaffold widget cannot be marked as needing to build
because the framework is already in the procces

Check out https://flutter.io/docs/cookbook/design/snackbars – Khurshid Ansari Dec 26 '18 at 06:39 — Khurshid Ansari, Dec 26 '18 at 06:39

diegoveloper · Answer 1 · 2018-12-26T06:25:13.170

4

That's because you shouldn't display a Snackbar while your Widget is the process of rebuilding, a workaround that you can use is :

          _displaySnackBar(BuildContext context) async {
            await Future.delayed(Duration(milliseconds: 400));
            scaffoldKey.currentState.showSnackBar(SnackBar(
              content: Container(
                height: 100,
              ),
            ));
          }

and

   if (snap.hasError) {
          _displaySnackBar(context);
          return Center(child: Text(snap.error));
        }

edited Dec 26 '18 at 06:25

answered Dec 26 '18 at 06:07

diegoveloper

93,875
20
236
194

Ooh sorry I posted a wrong code, conditional to check doesn't work as well – Tornike Kurdadze Dec 26 '18 at 06:09
now it works but what if building process take mot than 400 mls? – Tornike Kurdadze Dec 26 '18 at 06:30
that's is not about the process time , that time is after you receive the data from your stream , I added an extra delay after your widget is refreshed. – diegoveloper Dec 26 '18 at 06:32
also you can check this answer :) https://stackoverflow.com/questions/52849373/error-when-i-try-to-show-a-snackbar-in-a-builder – diegoveloper Dec 26 '18 at 06:35

score 0 · Answer 2 · answered Jan 03 '19 at 13:56

0

It's a workarround but worked for me

Future<void> _snackBar(String text, context) async {
    Scaffold.of(context).showSnackBar(Helper.snackBarInfo(text));
}

answered Jan 03 '19 at 13:56

limars

56
3

score 0 · Answer 3 · edited Jun 17 '20 at 17:54

StreamBuilder(
    stream: bloc.stream,
    builder: (BuildContext context,
        AsyncSnapshot snapshot) {
      if (snapshot.hasData) {
        SchedulerBinding.instance
              .addPostFrameCallback((_) {
            Scaffold.of(context).showSnackBar(
              SnackBar(
                content: Text(
                        snapshot.data.error,
                        style: TextStyle(fontSize: 16)),
                duration: Duration(seconds: 3),
              ),
            );
          }); 
      }
      return Container();
    }),

Flutter show SnackBar and return empty Container in StreamBuilder throws an Error

3 Answers3