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我是 bloc 的新手，我有静态数据，需要使用数据层“存储库和模型”编写干净的代码，然后在 initstate 中写入这一行，加载小部件只能工作，但我发现我应该在 initstate 中编写 cubit dunction要发出加载状态，请注意我没有使用加载状态。只是初始和加载有这个错误

TypeError: Cannot read properties of null (reading 'getAllPostsRep')

The relevant error-causing widget was
LayoutBuilder LayoutBuilder:file:///C:/Users/Michael/Desktop/task/New/lib/presentation/screens/home_screen.dart:34:24
When the exception was thrown, this was the stack
packages/facebookui/business_logic/cubit/posts_cubit.dart 15:38                                                       getAllPosts

在 initstate 中写下这一行之后

class _FeedState extends State<Feed> {
  List<PostModel> allPosts = [];

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

  @override
  Widget build(BuildContext context) {
    return Expanded(
      flex: 2,
      child: Align(
        alignment: AlignmentDirectional.topStart,
        child: SingleChildScrollView(
          child: Align(
            alignment: AlignmentDirectional.topStart,
            child: Column(
              children: [
                Stories(), //stories widget
                Card(
                  child: Column(
                    children: [
                      WhatsOnYourMind(), //img,textfield of create post
                      CustomDivider(),
                      LiveSection(), //live, video and photos section
                      SizedBox(
                        height: 20,
                      )
                    ],
                  ),
                ),
                //create room and rooms
                Rooms(),
                //all posts
                BlocBuilder<PostsCubit, PostsState>(
                  builder: (context, state) {
                    if (state is PostsLoaded) {
                      setState(() {
                        allPosts = (state).postsList;
                      });
                      return Posts(allPosts: allPosts);
                    } else {
                      return Loading();
                    }
                  },
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

这是从 fly post 获取静态数据的存储库

class PostsRepository {
  //charactersWebServices

  Future<List<PostModel>> getAllPostsRep() async {
    await Future.delayed(const Duration(seconds: 2));
    //posts is a const data
    return posts;
  }
}

这是状态

part of 'posts_cubit.dart';

@immutable
abstract class PostsState {}

class PostsInitial extends PostsState {}

class PostsLoaded extends PostsState {
  final List<PostModel> postsList;
  PostsLoaded(this.postsList);
}

这是肘

class PostsCubit extends Cubit<PostsState> {
  final PostsRepository postsRepository;
  List<PostModel> allposts = [];

  PostsCubit(this.postsRepository) : super(PostsInitial());

  List<PostModel> getAllPosts() {
    postsRepository.getAllPostsRep().then((value) {
      emit(PostsLoaded(value));
      allposts = value;
    });
    return allposts;
  }
}

这是常量数据

List<PostModel> posts = [
  PostModel(
      name: 'Abdullah Ghayad',
      time: 5,
      text:
          'The APIC Text is the most comprehensive and up-to-date reference for infection prevention and control (IPC). Written, edited, and reviewed by more than 200 subject matter experts, it reflects the latest guidelines, regulations, and standards of practice.The APIC Text\’s 11 sections and 125 peer-reviewed chapters are broad ranging, covering everything from fundamental principles, microbiology, epidemiology, and surveillance to more specialized topics, including specialty care populations, special pathogens, occupational health, and supportive care.',
      comments: 5,
      like: 50,
      profileImage:
          'http://c.files.bbci.co.uk/C870/production/_112921315_gettyimages-876284806.jpg',
      images: [
        'https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSCZlf5lc5tX-0gY-y94pGS0mQdL-D0lCH2OQ&usqp=CAU'
      ]),
]
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1 回答 1

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因为postsRepository为null，所以需要初始化

  final PostsRepository postsRepository = PostsRepository();

并将其从构造函数中移除

于 2021-10-03T15:56:59.540 回答