Triggering initial event in BLoC

Your discomfort really has reason – no event should be fired from build() method (build() could be fired as many times as Flutter framework needs)

Our case is to fire initial event on Bloc creation

Possibilities overview

1. case with inserting Bloc with BlocProvider – this is preferred way

create: callback is fired only once when BlocProvider is mounted & BlocProvider would close() bloc when BlocProvider is unmounted

    class ExampleScreenState extends StatelessWidget {
    
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          body: BlocProvider(
            create: (context) => ExampleBloc()..add(Fetch()), // <-- first event, 
            child: BlocBuilder<ExampleBloc, ExampleState>(
              builder: (BuildContext context, state) {
                ...
              },
            ),
          ),
        );
      }
    }

2. case when you create Bloc in State of Statefull widget

class _ExampleScreenStateState extends State<ExampleScreenState> {
  ExampleBloc _exampleBloc;

  @override
  void initState() {
    super.initState();
    _exampleBloc = ExampleBloc();
    _exampleBloc.add(Fetch());
    // or use cascade notation
    // _exampleBloc = ExampleBloc()..add(Fetch());
  }

  @override
  void dispose() {
    super.dispose();
    _exampleBloc.close(); // do not forget to close, prefer use BlocProvider - it would handle it for you
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: BlocBuilder<ExampleBloc, ExampleState>(
        bloc: _exampleBloc,
        builder: (BuildContext context, state) {
         ...
        },
      ),
    );
  }
}

3. add first event on Bloc instance creation – this way has drawbacks when testing because first event is implicit

class ExampleBloc extends Bloc<ExampleEvent, ExampleState> {

  ...

  ExampleBloc() {
    add(Fetch());
  }
}

// insert it to widget tree with BlocProvider or create in State
BlocProvider( create: (_) => ExampleBloc(), ...

// or in State

class _ExampleScreenStateState extends State<ExampleScreenState> {
  final _exampleBloc = ExampleBloc(); 
...

PS feel free to reach me in comments