Actions That Don't Change State

In AsyncRedux, returning a new state from reducers is optional. When you don't need to modify the application state, return null to keep the current state unchanged.

Basic Pattern

Return null from reduce() when no state modification is needed:

class MyAction extends ReduxAction<AppState> {
  AppState? reduce() {
    // Perform side effects here
    return null; // State remains unchanged
  }
}

Conditional State Updates

Only update state when certain conditions are met:

class GetAmount extends ReduxAction<AppState> {
  Future<AppState?> reduce() async {
    int amount = await getAmount();
    if (amount == 0)
      return null; // No change needed
    else
      return state.copy(counter: state.counter + amount);
  }
}

Coordinating Other Actions

Actions that dispatch other actions but don't modify state directly:

class InitAction extends ReduxAction<AppState> {
  AppState? reduce() {
    dispatch(ReadDatabaseAction());
    dispatch(StartTimersAction());
    dispatch(TurnOnListenersAction());
    return null; // This action doesn't change state itself
  }
}

Triggering External Services

Call external services without modifying app state:

class SendNotification extends ReduxAction<AppState> {
  final String message;
  SendNotification(this.message);

  Future<AppState?> reduce() async {
    await notificationService.send(message);
    return null;
  }
}

Navigation Actions

Trigger navigation as a side effect:

class GoToSettings extends ReduxAction<AppState> {
  AppState? reduce() {
    dispatch(NavigateAction.pushNamed('/settings'));
    return null;
  }
}

Key Points

Actions that do return a new state can also do side effects and dispatch other actions.
Return type matters: Use AppState? for sync, Future<AppState?> for async
Null means no change: The store keeps its current state

References

URLs from the documentation:

https://asyncredux.com/flutter/basics/changing-state-is-optional
https://asyncredux.com/flutter/basics/actions-and-reducers
https://asyncredux.com/flutter/basics/sync-actions
https://asyncredux.com/flutter/basics/async-actions
https://asyncredux.com/flutter/advanced-actions/redux-action
https://asyncredux.com/flutter/advanced-actions/before-and-after-the-reducer