Flutter bloc naming

Flutter BLoC naming

For flutter_bloc + freezed. Extends the official BLoC naming convention with stricter event names and a freezed-aware factory shape.

Events

Public class names

Freezed generates = _Load for a union member by default. Override it to a public class so the UI can call the constructor directly without going through the Event.factory() indirection.

@freezed
sealed class LoginEvent with _$LoginEvent {
  const factory LoginEvent.started() = LoginStarted;
  const factory LoginEvent.usernameChanged(String value) = LoginUsernameChanged;
  const factory LoginEvent.passwordChanged(String value) = LoginPasswordChanged;
  const factory LoginEvent.submitted() = LoginSubmitted;
}

bloc.add(LoginStarted());                       // good
bloc.add(LoginEvent.started());                 // avoid (extra indirection)

Past tense, domain-neutral

An event describes what happened in the domain, not what the UI did. A domain event survives the button being swapped for a swipe, a back-press, or a programmatic trigger.

// good
LoginSubmitted, LogoutRequested, SessionFinished
UsernameChanged, ProfileTabSelected, FavoriteToggled
TimerTicked, SyncTicked
Started, Initialized, ItemsRefreshed

// bad: imperative, reads like a command
LoadData, StartSession, CancelSession

// bad: pinned to a UI trigger
SubmitButtonPressed, LaunchButtonClicked, CancelTapped

Common shapes:

• User action: <Verb>Requested (trigger-neutral) or <Thing>Submitted for a form submit.
• Value change: <Field>Changed, <Thing>Selected, <Thing>Toggled.
• System: <Thing>Ticked, <Thing>Started, <Thing>Finished.
• Screen lifecycle: Started (the BLoC community default for "ready, load data") and Closed.

Pressed, Clicked, Tapped are forbidden. This is stricter than the official convention, which allows Pressed. The trade-off is fewer renames when the UI changes.

Feature prefix

To avoid collisions across BLoCs and to keep events globally readable:

LoginStarted              // good
ProfileEditorStarted      // good
Started                   // too generic

Factory name matches class name

const factory LoginEvent.started() = LoginStarted;
const factory LoginEvent.usernameChanged(String value) = LoginUsernameChanged;

started ↔ Started, usernameChanged ↔ UsernameChanged. No surprises.

Sealed

Events are sealed (requires freezed 3.0+) so exhaustive switches catch unhandled cases at compile time.

@freezed
sealed class LoginEvent with _$LoginEvent { ... }

States

Sealed class, public variants, present-tense names. The name describes the current state, not the transition into it.

@freezed
sealed class LoginState with _$LoginState {
  const factory LoginState.initial() = LoginInitial;
  const factory LoginState.loading() = LoginLoading;
  const factory LoginState.success() = LoginSuccess;
  const factory LoginState.failure({required Exception e}) = LoginFailure;
}

// good: present-tense, current state
Initial, Loading, Loaded, Saving, Success, Failure, Empty
Setup, Running, Paused, Finished, Cancelled

// bad: reads like an event
LoadSucceeded, StartedLoading, ShowError

Handlers

Handler name is _on<EventSuffix>, where EventSuffix is the part of the event class after the feature prefix. No feature prefix on the handler itself, it is already local to the BLoC.

on<LoginStarted>(_onStarted);
on<LoginUsernameChanged>(_onUsernameChanged);
on<LoginSubmitted>(_onSubmitted);

Future<void> _onStarted(LoginStarted event, Emitter<LoginState> emit) async { ... }
void _onUsernameChanged(LoginUsernameChanged event, Emitter<LoginState> emit) { ... }

Checklist

• Event class is public, not _Load.
• UI calls the constructor directly, not the factory.
• Event is in past tense.
• Event has no Pressed / Clicked / Tapped suffix.
• Event has a feature prefix (LoginStarted, not bare Started).
• Event class is sealed.
• State class is sealed, state variants are public.
• Handler is _on<EventSuffix>, no feature prefix.

References

• Official BLoC naming convention