here I am getting all the following ids and storing in list of string

  List<String> followinguserid = [];
  Future<QuerySnapshot> _timelinepoststream;
  getAllFollowingId() async {
    String currentuserid = await UserSecureStorage.getUserId();
    print(currentuserid);
    await followingRef
        .doc(currentuserid)
        .collection('userFollowing')
        .get()
        .then((QuerySnapshot querySnapshot) {
      querySnapshot.docs.forEach((element) {
        followinguserid.add(element.id);
      });
    });
 
  }

in init function i am making the query

  @override
  void initState() {
    // TODO: implement initState
    super.initState();

    getAllFollowingId();
    _timelinepoststream = FirebaseFirestore.instance
        .collection('posts')
        .where('UserIds', arrayContainsAny: [
     ...followinguserid
    ]).get();
  }

here i am using future builder and passing the future

  @override
  Widget build(BuildContext context) {
    var width = MediaQuery.of(context).size.height;
    var height = SizeConfig.getHeight(context);
    return FutureBuilder(
        future: _timelinepoststream,
        builder: (context, snapshot) {
          List<DocumentSnapshot> documents;
          if (snapshot.connectionState == ConnectionState.done) {
            print(snapshot.data.docs);
            documents = snapshot.data.docs;
            return Text("sample");
            }})}

I am getting this error

CodePudding user response：

Since getAllFollowingId is an async method, you need to use await when calling it:

await getAllFollowingId();

Without await your database query runs before the followinguserid has been populated, which explains the error message.

If you can't use await, you can also use a then() callback:

getAllFollowingId().then(() {
  _timelinepoststream = FirebaseFirestore.instance
      .collection('posts')
      .where('UserIds', arrayContainsAny: [
   ...followinguserid
  ]).get();
})