CODEWITHSUNDEEP
firebaseflutterdart
Hampus Ekedahl
Hampus Ekedahl

Reputation: 31

How can i return a List as Future<List>? - Flutter

im trying to randomly get documents from firebase. Since .where(FieldPath.documentId, whereIn: element) only supports lists of 10 elements i split my list to sublists and run each query based on the sublists. When result from each query is returned i try adding them to an List<DocumentSnapshot<Object?>> results = [];

This List is then returned and my problem is that the screen displays error, but if i reload the screen it works. I think the problem is that my function wants to return

Future<List<DocumentSnapshot>> getBeerPongCards1() async {

But my List is List<DocumentSnapshot<Object?>> results = [];

Future<List<DocumentSnapshot>> getBeerPongCards1() async {
    List<DocumentSnapshot<Object?>> results = [];

    List<String> IdList = List<String>.generate(20, (counter) => "$counter");
    IdList.shuffle();

    List<List<String>> subList = [];
    for (var i = 0; i < IdList.length; i += 10) {
      subList.add(
          IdList.sublist(i, i + 10 > IdList.length ? IdList.length : i + 10));
    }

    subList.forEach((element) async {
      await FirebaseFirestore.instance
          .collection('beerpong1')
          .where(FieldPath.documentId, whereIn: element)
          .limit(10)
          .get()
          .then((value) async {
        results.addAll(value.docs);
      });
    });

    return results;
  }

I dont know if my question made any sense but im thankful for any help:D

Upvotes: 2

Views: 414

Answers (1)

Michael Horn
Michael Horn

Reputation: 4089

The issue is likely that when you use sublist.forEach, that for loop is not awaited, so you return an empty list (in any case, that should be handled in a graceful way for the user).

Instead of using a .forEach function, use a regular for loop - That way, each element will be awaited properly, and the list will be populated when the function returns:

for (final element in subList) {
  await FirebaseFirestore.instance
      .collection('beerpong1')
      .where(FieldPath.documentId, whereIn: element)
      .limit(10)
      .get()
      .then((value) async {
        results.addAll(value.docs);
      });
}

Upvotes: 1

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