Flutter: bloc, how to show an alert dialog

Question

I´m new in the bloc pattern and stream stuff. I want to show up an alert dialog when I press a button, but I can´t find a way to do it. Actually my code is:

Widget button() {
  return RaisedButton(
      child: Text('Show alert'),
      color: Colors.blue[700],
      textColor: Colors.white,
      onPressed: () {
        bloc.submit();
      });
   }



return Scaffold(
        appBar: AppBar(
          title: Text("Title"),
        ),
        body: StreamBuilder(
            stream: bloc.getAlert,
            builder: (context, snapshot) {
              if (snapshot.hasData) {
                return Text("I have Dataaaaaa ${snapshot.data}");
              } else
                return ListView(
                  children: <Widget>[
                    Container(
                     button()
                    )
                ...

And the BLoC:

final _submissionController = StreamController();
Stream get submissionStream=> _submissionController.stream;
Sink get submissionSink=> _submissionController.sink;

I tried to do something like:

Widget button() {
  return StreamBuilder(
stream: submissionStream
builder: (context, snapshot){
if (snapshot.hasData){
return showDialog(...)
}else
 return RaisedButton(
      child: Text('Show alert'),
      color: Colors.blue[700],
      textColor: Colors.white,
      onPressed: () {
        bloc.submit();
      });
   }

But, of course, it didn´t work.

Answer 1

You can't show a dialog when build working. When you have new data, then you create a new widget. Probably better for you will be not using the stream in this case, but if it necessary you should use

WidgetsBinding.instance.addPostFrameCallback((_) => yourFunction(context));

or

Future.microtask(() => showDialogFunction(context));

in your if

if (snapshot.hasData) { WidgetsBinding.instance.addPostFrameCallback((_) => showDialogFunction(context)); }

This code will be launched after build method, so dialog will show immediately.

Bloc function always return widget, so always return button() or different wiget when stream has data