无法获取StreamBuilder数据，报错_ControllerStream不是Iterable子类型

问题原因 #

• 第一处错误在getChatData的实现：你当前yield的是getChat(id).asStream()，也就是每次向流中推送的是另一个Stream对象，而不是接口返回的消息列表数据，所以snapshot.data拿到的是流对象而非可遍历的列表，触发类型不匹配报错
• 第二处错误在getChat的实现：async和then混用导致你没有正确把消息列表作为Future的返回值返回，接口请求到的列表没有被正确传递出去，所以会出现snapshot.data为空的情况

修复代码 #

1. 修正getChat函数，正确返回消息列表 #

把then写法改为更清晰的await写法，显式返回最终的消息列表，同时过滤接口返回末尾多余逗号生成的空消息：

Future<List> getChat(orderId) async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  var _token = prefs.getString('token');
  print('The Latest Order Token is $_token');

  final Map<String, dynamic> body = {
    "id": "$orderId",
  };
  final List _messageData = [];

  var url = Uri.parse('$_server/api/driver/get/convo/?access_token=$_token');

  http.Response response = await http.post(url, body: body, headers: {
    "Content-Type": 'application/x-www-form-urlencoded'
  });
  print(response.body);

  switch (response.statusCode) {
    case 200:
      final Map<String, dynamic> responseData = json.decode(response.body);
      print("The ${response.body}");
      var x = responseData['message_data'].split(",");
      print(x);
      for (int i = 0; i < x.length; i++) {
        // 过滤空字符串，避免接口返回末尾逗号生成的空消息
        if(x[i].trim().isNotEmpty) {
          _messageData.add(x[i]);
          print(x[i]);
        }
      }
      print(x);
      break;
    default:
      final Map<String, dynamic> responseData = json.decode(response.body);
      print(responseData);
      break;
  }
  return _messageData;
}

2. 修正getChatData函数，推送正确的列表数据 #

不要把Future转成Stream推送，直接await拿到列表后推送列表本身：

Stream<List> getChatData(Duration refreshTime, id) async* {
  while (true) {
    await Future.delayed(refreshTime);
    yield await getChat(id);
  }
}

3. 可选优化StreamBuilder的状态处理 #

补充加载、错误状态的展示，同时拆分消息字段区分发送者和消息内容：

StreamBuilder(
  stream: _chatStream,
  builder: (context, snapshot) {
    if (snapshot.connectionState == ConnectionState.waiting) {
      return const Center(child: CircularProgressIndicator());
    }
    if (snapshot.hasError) {
      return Center(child: Text('加载失败：${snapshot.error}'));
    }
    if (snapshot.hasData) {
      final messages = snapshot.data as List;
      List<MessageBubble> messageWidgets = [];
      for (var message in messages) {
        // 拆分消息内容区分发送者、消息文本
        final splitMsg = message.split(' - ');
        final senderAndContent = splitMsg[1].split(': ');
        final msgSender = senderAndContent[0];
        final msgText = senderAndContent[1];
        
        final currentUser = "loggedInUser.displayName";
        final msgBubble = MessageBubble(
          msgText: msgText,
          msgSender: msgSender,
          user: currentUser == msgSender
        );
        messageWidgets.add(msgBubble);
      }
      return Expanded(
        child: ListView(
          reverse: true,
          padding: const EdgeInsets.symmetric(vertical: 15, horizontal: 10),
          children: messageWidgets,
        )
      );
    }
    return const Center(child: Text('暂无聊天消息'));
  },
),

内容的提问来源于stack exchange，提问作者Doing Things Occasionally