Flutter Firestore getDocuments() not working on initState

Question

I'm having an issue trying to call a document from Firestore in initState. I can pull data from a StreamBuilder just fine, but I just want to call the data once on initState.

Here is what I'm doing:

class _PainLevelState extends State<PainLevel> {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final CollectionReference userCollection =
      Firestore.instance.collection('users');
  static final now = DateTime.now();
  String _uid;
  double myPainLevel = 0;

  Future<void> getCurrentUser() async {
    final FirebaseUser user = await _auth.currentUser();
    if (mounted) {
      setState(() {
        _uid = user.uid;
      });
    }
  }

  Future<void> getCurrentPainLevel() async {
    await userCollection
        .document(_uid)
        .collection('pain')
        .where('time',
            isGreaterThanOrEqualTo: DateTime(now.year, now.month, now.day))
        .getDocuments()
        .then((QuerySnapshot docs) {
      if (docs.documents.isNotEmpty) {
        print('yes');
      } else {
        print('no'); 
      }
    });
  }

  @override
  void initState() {
    super.initState();
    getCurrentUser();
    getCurrentPainLevel();
  }

...

I just get a "no" every time I print to console. It's not get any documents when there is one. If I take the same code inside the future and put it somewhere else, like in the build method, it works, but it constantly builds and I don't want that. Any suggestion as to why it is not working? Thanks in advance.

Solution

I'm guessing here that your code will not always work, because getCurrentPainLevel might get called before getCurrentUser is completed, which will cause _uid to be null and therefore, not work as expected. Try to put then keyword after getCurrentUser method, like this:

@override
  void initState() {
    super.initState();
    getCurrentUser().then((_) {
      getCurrentPainLevel();
    });
  }

By the way, you should NOT be calling async methods in initState. Try to put the code somewhere else, like WidgetsBinding.instance.addPostFrameCallback(...).

Comments

[Michael]

That makes sense now. Thank you! I changed the initState to WidgetsBinding.instance.addPostFrameCallback((_) => getCurrentPainLevel()); and just added final FirebaseUser user = await _auth.currentUser(); to the getCurrentPainLevel() method, and changed _uid to user.uid. It works now. :)