这通常是因为Bloc builder的initialState返回了一个String类型，但Bloc的State类型是int。解决方法是确保initialState返回一个int类型值。以下是一个示例代码：

class MyBloc extends Bloc {
  @override
  int get initialState => 0;

  @override
  Stream mapEventToState(MyEvent event) async* {
    if (event is IncrementEvent) {
      yield state + 1;
    } else if (event is DecrementEvent) {
      yield state - 1;
    }
  }
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocBuilder(
      builder: (context, state) {
        return Text(
          '$state',
        );
      },
    );
  }
}