Flutter 肘初始化状态

Question

I am at the begin of my Cubit learning and i tried to create a "Liter-Tracker" with sharedPrefs. Everything works but not the init state. I have to press a Button first because I initialize the drinkValue with 0. I tried to return an Int with the value from shared prefs but this dont work:( May you help me?

This is my cubit:

class DrinkCubit extends Cubit<DrinkState> {
  DrinkCubit() : super(DrinkState(drinkValue: 0));


  Future<void> loadCounter() async {
    final prefs = await SharedPreferences.getInstance();

    state.drinkValue = (prefs.getInt('counter') ?? 0);
  }


  Future<int> loadInitCounter() async {
    final prefs = await SharedPreferences.getInstance();

    return state.drinkValue = (prefs.getInt('counter') ?? 0);
  }

}

and this my cubit state:

class DrinkState {
  int drinkValue;
  int? amount;

  DrinkState({
    required this.drinkValue,

});

}

I also tried something like this in my MainPage, how i usually init my state with setState:

  @override
  void initState() {
    super.initState();
    BlocProvider.of<DrinkCubit>(context).loadCounter();
  }

Answer 1

Context is not accessible in initstate, try using didChangeDependencies life cycle method Flutter get context in initState method

Answer 2

Firstly, I strongly advise you to avoid the StatefulWidget when you use BLoC, but it doesn't mean you can't use it at all. Just be careful because setState() can rebuild BlocProvider inside the stateful widget.

As for the initialization process, I suggest you use this approach on the BlocProvider.

class DrinkScreen extends StatelessWidget {
  const DrinkScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return BlocProvider(
      create: (context) => DrinkCubit()..loadCounter(), // Or call other initialization method
      child: DrinkView(),
    );
  }
}

This approach works really well if you reuse this screen multiple times, for example, you redirect to DrinkScreen every time you want to fill data and you dispose of the screen afterward ( Navigate.pop() , etc). This way you can automatically initialize the cubit every time you redirect into this screen, you don't need to use StatefulWidget to init the cubit.