我的MessagesBloc类做错了什么?我应该如何创建它？

Question

Lorem Ipsum只是印刷和排版行业的虚拟文本。自15世纪以来，Lorem Ipsum一直是业界的标准虚拟文本，当时一家不知名的印刷商拿出了一个排版，然后把它弄乱了，做成了一个排版样本簿。它不仅存活了五个世纪，还经历了电子排版的飞跃，基本上保持不变。它在20世纪60年代随着包含Lorem Ipsum段落的Letraset sheets的发布而流行起来，最近又随着包括Lorem Ipsum版本的桌面出版软件Aldus PageMaker而流行起来。

Answer 1

如果父部件中没有BlocProvider，则需要创建一个阻塞实例，并为BlocBuilder提供一个阻塞。

MessageBloc _messageBloc = MessageBloc(databaseService: someDatabaseServicInstance);
...

    Widget build(BuildContext context) {
           return BlocBuilder<MessagesBloc, MessagesState>(
        bloc: _messageBloc,
        builder: (context, state) {
      if (state is Loading) {
        return LoadingIndicator();
      }
      if (state is Finished) {
        messages = state.messages;
        return messages.length != 0
            ? _buildMessageView(messages)
            : _buildEmptyMessageView();
      }
    });
};

Answer 2

-> AddMessage -> BlocListener listen AddMessageComplete event -> replace messages变量来自state.messages (您应该添加AddMessage事件的状态，如AddMessageFinished或AddMessageComplete)

List<Message> messages = [];
MessageBloc _messageBloc = BlocProvider.of<MessagesBloc>(context);

  @override
  void initState() {
    super.initState();
    _firebaseMessaging.configure(
      onMessage: (Map<String, dynamic> message) async {
        print("onMessage: $message");

        var result = Message.fromMap(
            new Map<String, dynamic>.from(message['notification']));

         // I exactly don't know it works, if not works use yours.
        _messageBloc.add(
          AddMessage(message: result),
        );

        //setState(() {
        //  messages.add(result);
        //});
      },
  }

    Widget build(BuildContext context) {
      return BlocConsumer<MessagesBloc, MessagesState>(
        listener: (context, state) {
           if (state is AddCompleted) {
              setState(() {
                messages = state.messages;
              }
           }
        },
        builder: (context, state) {
          if (state is Loading) {
            return LoadingIndicator();
          }
          if (state is Finished) {
            messages = state.messages;
            return messages.length != 0
                ? _buildMessageView(messages)
                : _buildEmptyMessageView();
          }
        },
      }
    );
  }