在从 flutter 中的 Firestore 加载数据之前出现错误

Question

Here when i try to load data in my flutter app, before loading data it throws an error for 1 second then it displays the data, here is the error:

here is my code:

  class MapScreenState extends State<DashboardPage> {

  Stream<DocumentSnapshot> getData() async*{
    var user = await FirebaseAuth.instance.currentUser();
    yield* Firestore.instance.collection('Profile').document(user.uid).snapshots();
  }
  @override
  void initState() {
    super.initState();

    getData();//until this is completed user stays null we can use it to check whether it's loaded
  }

  @override
  Widget build(BuildContext context) {

    return StreamBuilder(
      stream: getData(),
      builder: (context, snapshot) {

        if (snapshot.hasError) {
          return new showProfile(
            name: "anonymous",
            email: "null",
            pin: "null",
            address: "null",
          );
        }else {
          var userDocument = snapshot.data;
          return new showProfile(
            name: userDocument['name'],
            email: userDocument["email"],
            pin: userDocument["pin"],
            address: userDocument["address"],
          );
        }

      },
    );
  }
}

How can i retrieve the data without showing the error?

Answer 1

Somewhere in your code there is a Text widget that is being given a string from firestore before the string is loaded. Try doing this:

...

Text(stringFromFirestore ?? ''),

...

In dart, the ?? operator checks if the first value (stringFromFirestore) is null, and if it is not, it returns the first value, but if it is, it returns the second value.