Global snackbar/dialog utils class in flutter

Question

I want to create a GlobalMessageUtils class that would open a material snackbar or dialog without having to pass the build context. The idea is that whenever there's any error (no network, bad request, etc) I am able to pop open a snackbar and relay the message to the user.Is there a concept of global context?

I was playing with the idea of making my GlobalMessageUtils class a singleton that takes in a build context and instantiate it at the MaterialApp level, but I haven't gotten this to work. Any body have any ideas? Is this even a good pattern in flutter? If not, how do you guys deal with error handling at a global level?

Answer 1

Using the BLOC pattern and Rxdart, I created a UiErrorUtils class

class UiErrorUtils {
 // opens snackbar
  void openSnackBar(BuildContext context, String message) async {
    await Scaffold.of(context).showSnackBar(
      SnackBar(
        content: Text(message),
      ),
    );
  }
  // subscribes to stream that triggers open snackbar
  void subscribeToSnackBarStream(BuildContext context, PublishSubject<String> stream){
    stream.listen((String message){
      openSnackBar(context, message);
    });
  }
}

In your StatefulWidget, you can use the context provided in the initState hook:

class WidgetThatUsesUIErrorUtils extends StatefulWidget {
  final UiErrorUtils uiErrorUtils;
  final  Bloc bloc;

  WidgetThatUsesUIErrorUtils({this.uiErrorUtils, this.bloc});

  WidgetThatUsesUIErrorUtils createState() => WidgetThatUsesUIErrorUtilsState(
        uiErrorUtils: uiErrorUtils,
        bloc: bloc,
      );
}

class WidgetThatUsesUIErrorUtilsState extends State<WidgetThatUsesUIErrorUtils> {
  final Bloc _bloc;
  final UiErrorUtils _uiErrorUtils;

  WidgetThatUsesUIErrorUtilsState({Bloc bloc, UiErrorUtils uiErrorUtils})
      : _bloc = bloc ?? Bloc(),
        _uiErrorUtils = uiErrorUtils ?? UiErrorUtils();

  @override
  void initState() {
    super.initState();
    // Subscribe to UI feedback streams from  provided _bloc
    _uiErrorUtils.subscribeToSnackBarStream(context, _bloc.snackBarSubject);

  }

}

BLOC

class Bloc extends BlocBase {
  // UI Feedback Subjects
  final PublishSubject<String> snackBarSubject = PublishSubject<String>();

  //  some function that gets data from network
  Future<bool> getDataRequest() async {
     try {
      // get request code here
      } catch(error) {
      this.snackBarSubject.add(error);
    }

  }

  @override
  void dispose() {
    snackBarSubject?.close();
  }
}

Now your widget has subscribed to the bloc's snackBarStream. So in your bloc whenever a request fails you can add the message to the snackBarStream and since your widget has subscribed via UiErrorUtils the snackbar will trigger with the message.