不良狀態：使用StreamBuilder和Firestore時，Snapshot既沒有資料也沒有錯誤

我正在將資料從 Firestore 添加到Streamfrom StreamBuilder，但出現以下錯誤：

發生例外。StateError（壞狀態：快照既沒有資料也沒有錯誤

我的代碼。

class Home extends StatefulWidget {
  const Home({Key? key}) : super(key: key);

  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  AppState? estado;

  static String? userID = FirebaseAuth.instance.currentUser?.uid;
  static final userColeccion = FirebaseFirestore.instance.collection("users");

  var groupfav = ' ';
  Stream<QuerySnapshot>? taskGroup;

  @override
  void initState() {
    super.initState();
    getGroupFavData();
  }

  void getGroupFavData() async {
    var groupFavData = await userColeccion.doc("$userID").get();
    var groupfav = groupFavData.data()!['groupfav'];

    taskGroup = FirebaseFirestore.instance
        .collection("groups")
        .doc(groupfav) // pass the obtained value
        .collection("task")
        .snapshots();
  }

  @override
  Widget build(BuildContext context) {
    estado = Provider.of<AppState>(context, listen: true);
    return Scaffold(
      appBar: AppBar(
        title: const Text("Home"),
        automaticallyImplyLeading: false,
      ),
      body: StreamBuilder(
        stream: taskGroup,
        builder: (
          BuildContext context,
          AsyncSnapshot<QuerySnapshot> snapshot,
        ) {
          if (snapshot.hasError) {
            return const Text("error");
          }
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const Text("Loading");
          }
          var data = snapshot.requireData;

          return ListView.builder(
            itemCount: data.size,
            itemBuilder: (context, index) {
              return Card(
                child: ListTile(
                  title: Text("${data.docs[index]['titulo']}"),
                  subtitle: Text("${data.docs[index]['contenido']}"),
                  onTap: () {},
                  trailing: IconButton(
                    icon: const Icon(Icons.delete),
                    color: Colors.red[200],
                    onPressed: () {},
                  ),
                ),
              );
            },
          );
        },
      ),
    );
  }
}

uj5u.com熱心網友回復：

好的，看看你的問題，我知道 1）你需要在開始監聽該檔案之前獲取檔案的資料，這很正常，所以你想先呼叫集合，獲取檔案，然后監聽名為task的檔案集合，這是有道理的。您的問題仍然是異步問題。該應用程式正在重建尚未到達的流；你必須修復事情的順序。

然后，您需要稍微改變一下并執行以下操作：

選項＃1：a）使用FutureBuilder：這將允許您進行異步呼叫以根據用戶ID獲取檔案名稱b）在獲得與該用戶關聯的檔案后，您想監聽由產生的流該集合在該檔案中稱為任務。在那里你可以連接StreamBuilder。

選項#2 : a) 保持原樣，但聽任務組快照；但隨著值到達該集合，請繼續重建串列。

這些是我的建議。

這是選項1的一些簡短代碼：

// .. in your Scaffold's body:

Scaffold(
 body: FutureBuilder( // the future builder fetches the initial data
   future: userColeccion.doc("$userID").get(),
   builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {

     if (snapshot.hasData) {
       var groupfav = snapshot.data()!['groupfav'];

       // then once the 'groupfav' has arrived, 
       // start listening on the taskGroup

       taskGroup = FirebaseFirestore.instance
        .collection("groups")
        .doc(groupfav) // pass the obtained value
        .collection("task")
        .snapshots();

       return StreamBuilder(
           stream: taskGroup,
           builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
          // the rest of your code

       });
     }

     return CircularProgressIndicator();
   }
)

)

選項 2 類似于：

List<Task> userTasks = [];

void getGroupFavData() async {
    var groupFavData = await userColeccion.doc("$userID").get();
    var groupfav = groupFavData.data()!['groupfav'];

    taskGroup = FirebaseFirestore.instance
        .collection("groups")
        .doc(groupfav) // pass the obtained value
        .collection("task")
        .snapshots().listen((snapshot) {
          // here populate a list of your tasks
          // and trigger a widget rebuild once you've grabbed the values
          // and display it as a list on the UI

          setState(() {

            userTasks = snapshot.docs.map((d) => Task.fromJson(d.data())).toList();
          });
 
       });
  }

And in your Scaffold, you can have a ListView just rendering the items on that task list, like:

ListView.builder(
  itemCount: userTasks.length,
  itemBuilder: (context, index) {
     // render your tasks here
  })

Here's a

Hope those pointers take you somewhere.

標籤：火力基地 扑 镖 谷歌云火库

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