How to handle returning an AsyncError when initializing the provider?

[devnta]

Official doc says:

class AsyncTodosNotifier extends AsyncNotifier<List<Todo>> {
  Future<List<Todo>> _fetchTodo() async {
    final json = await http.get('api/todos');
    final todos = jsonDecode(json) as List<Map<String, dynamic>>;
    return todos.map(Todo.fromJson).toList();
  }

  @override
  Future<List<Todo>> build() async {
    // Load initial todo list from the remote repository
    return _fetchTodo();
  }

  Future<void> addTodo(Todo todo) async {
    // Set the state to loading
    state = const AsyncValue.loading();
    // Add the new todo and reload the todo list from the remote repository
    state = await AsyncValue.guard(() async {
      await http.post('api/todos', todo.toJson());
      return _fetchTodo();
    });
  }

  // Let's allow removing todos
  Future<void> removeTodo(String todoId) async {
    state = const AsyncValue.loading();
    state = await AsyncValue.guard(() async {
      await http.delete('api/todos/$todoId');
      return _fetchTodo();
    });
  }

  // Let's mark a todo as completed
  Future<void> toggle(String todoId) async {
    state = const AsyncValue.loading();
    state = await AsyncValue.guard(() async {
      await http.patch(
        'api/todos/$todoId',
        <String, dynamic>{'completed': true},
      );
      return _fetchTodo();
    });
  }
}

// Finally, we are using NotifierProvider to allow the UI to interact with
// our TodosNotifier class.
final asyncTodosProvider =
    AsyncNotifierProvider<AsyncTodosNotifier, List<Todo>>(() {
  return AsyncTodosNotifier();
});

I want to show a dialog to display an error if _fetchTodos() throws an Exception or Error. How can I do that?
@rrousselGit Sorry for mention.
Thank you!

[snapsl]

Use ref.listen() like this and check for error state with next.hasError.

[devnta]

My question is, how can I trigger an error in the build method during the first initialization? If I set the state to AsyncError before the state is initialized, it causes an issue.

[zhxst]

In build method just throw an exception. the notifier will do the job for you.

[devnta]

That mean I just do like this:

@override
  Future<List<Todo>> build() async {
    // Load initial todo list from the remote repository
    return _fetchTodo();
  }

Future<List<Todo>> _fetchTodo() async {
   try {
    final json = await http.get('api/todos');
    final todos = jsonDecode(json) as List<Map<String, dynamic>>;
    return todos.map(Todo.fromJson).toList();
   } catch (e) {
   throw Exception('My exception'); // Add this?
   }
  }

[zhxst]

Exactly.

[devnta]

@zhxst
Is there any issue throw Error instead:

@override
  Future<List<Todo>> build() async {
    // Load initial todo list from the remote repository
    return _fetchTodo();
  }

Future<List<Todo>> _fetchTodo() async {
   try {
    final json = await http.get('api/todos');
    final todos = jsonDecode(json) as List<Map<String, dynamic>>;
    return todos.map(Todo.fromJson).toList();
   } catch (e) {
   throw Future.error(StateError('Error message')) // Add this?
   }
  }