Bloc: What is the best approach to pass data between pages?

[basketball-ico]

For example in a Todo App, but works for all type of apps

You have a TodosBloc that have events like LoadTodos, addTodo, DeleteTodo, ...

You have a TodosPage that show a list of all Todos, and have a DetailsPage that show all information of one todo selected.

When you select a Todo in TodosPage I want to show this Todo in DetailsPage

I see two approach for do that, but i don't know what is the best for BLoC, or maybe you can see other approach

1. pass a Todo like argument to DetailsPage

...
  itemBuilder: (BuildContext context, int index) {
    final todo = todos[index];
    return TodoItem(
      todo: todo,
      onTap: ()  {
        Navigator.of(context).push(
          MaterialPageRoute(builder: (_) {
            return DetailsScreen(id: todo.id);
          }),
        );
      }
    );
...

it is so simple, but i don't like that widgets pass this arguments, because all logic is better in a bloc, I think...

2. Set todo in a var in TodosBlocState

...
class TodoSelected extends TodosState {
  final Todo todo;
  TodoSelected(this.todo);
}
...

```dart
....
class SelectTodo extends TodosEvent {
final Todo todo;
SelectTodo(this.todo);
}
...

```dart
....
  Stream<TodosState> mapEventToState(
    TodosState currentState,
    TodosEvent event,
  ) async* {
    if (event is SelectTodo) {
      yield TodoSelected(event.todo);
    }
   ...
  }

...

...
  itemBuilder: (BuildContext context, int index) {
    final todo = todos[index];
    return TodoItem(
      todo: todo,
      onTap: ()  {
        todosBloc.dispatch(TodoSelected(todo));
        Navigator.of(context).push(
          MaterialPageRoute(builder: (_) {
            return DetailsScreen();
          }),
        );
      }
    );
...

[felangel]

@basketball-ico great question! 👍

I think both options are viable as they get the job done and are testable but I slightly prefer the 1st option because it is the "stateless" approach. I think by not having to persist the selected todo we reduce the complexity of the application and I personally tend to always pick the solution that involves maintaining as little state as possible. Let me know if that helps 😄

Also, you can check out the bloc library todo app in the flutter architecture samples for a concrete implementation.

[felangel]

@basketball-ico closing this for now but feel free to comment and I'll gladly reopen it 👍