如何将来自 Firestore 的用户名添加到 flutter 的应用栏中？

Question

So i have been trying to make an app in flutter, but i cannot seem to succeed in getting the username from the firestore database into a variable Here is my code!! EDIT:

final FirebaseAuth _auth = FirebaseAuth.instance;

Future<String> inputData() async {
  String _username = '';
  final userCol = Firestore.instance.collection("users");
  final FirebaseUser user = await _auth.currentUser();
  final uid = user.uid;

  // here you write the codes to input the data into firestorenull
  final data = await userCol.document(uid).get().then(
    (value) {
      final username = value.data["username"];
      _username = username;
      
    },
  );
  return _username;
}

I have tried it in many many different ways, as async, as future, with FutureBuilder etc but i cannot seem to find the solution. Here is the appbar:

   Widget build(BuildContext context) {
    var size = MediaQuery.of(context).size;
    return Stack(
      children: <Widget>[
        Scaffold(
          appBar: appbar.ProfileAppBar(name: _username)
............................................................

Answer 1

I think we need more information (such as whether or not you are successfully retrieving the username and it is getting properly set), but it looks like you aren't setting the state of the screen after getting the username.

Can you try

setState(() {
  final username = docs.data["username"];
  this._username = username;
});

Your function also appears to be incorrect. You are defining username as an empty string, and then defining an asynchronous function to get the username, and immediately returning username (the empty string). You will need to use a class variable and inside of the setstate, set the class variable as what you get from your asyncronous '.then()' function

Answer 2

So what i in fact did was to create a FutureBuilder, which helped a lot and i recommend it to everyone!!!