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

Solution

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));
        }

Comments

[Khurshid Ansari]

Check out flutter.io/docs/cookbook/design/snackbars

[Tornike Kurdadze]

Ooh sorry I posted a wrong code, conditional to check doesn't work as well

[Tornike Kurdadze]

now it works but what if building process take mot than 400 mls?

[diegoveloper]

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]

also you can check this answer :) stackoverflow.com/questions/52849373/…