Bloc: What is the proper way to fire an event (without a user pressing some button), right after a widget is a added in the tree?

[anuragvohraec]

Hi Felix/bloc team,

Thank you for this awesome framework, which has standardized my whole flutter development experience !

I have one question which keeps coming back to me.
What is the proper way to fire an event right after widget is addded to widget tree.

Say I have a captcha widget, the initial state of it is to show a circular progress indicator.
Now what is the right way to trigger event, without user interaction, to start the actual loading process of captcha from the network.

class Bloc_Captcha extends Bloc<Event_Captcha, State_Captcha> {
  Bloc_Captcha();

  @override
  State_Captcha get initialState => State_Captcha_loading();

  @override
  Stream<State_Captcha> mapEventToState(Event_Captcha event) async* {
    if (event is Event_Captcha_reload) {
      yield State_Captcha_loading();

      //lets fetch the captcha from internet
      var client = Client();
      try {
        var res = await client.get(event.url);

        yield State_Captcha_loaded(res.body);
      } catch (e) {
        yield State_Captcha_failed();
      }
    }
  }
}

Where exactly will I fire this event Event_Captcha_reload from, as it has to be done automatically without user pressing some button, right after this widget is added to the tree ?

[felangel]

Hi @anuragvohraec 👋
Thanks for opening an issue and for the positive feedback!

The easiest thing to do is fire the event from the create of BlocProvider

BlocProvider(
  create: (context) => Bloc_Captcha()..add(Event_Captcha_reload()),
  child: ...
),

Another option is you can create a StatefulWidget and in the State you can override initState and add the event there.

class _MyWidgetState extends State<MyWidget> {
  @override
  void initState() {
    super.initState();
    context.bloc<Bloc_Captcha>().add(Event_Captcha_reload());
  }
}

Hope that helps 👍