Flutter Firestore 如何将数组从 firestore 加载到列表

Question

I want to load the array from Firestore into a list in Flutter. I tried to use List.castFrom to convert Firestore array into List, but it does not work.

DocumentReference userDocRef = Firestore.instance.collection('users').document(id);
DocumentSnapshot userDocSnapshot = await userDocRef.get();

List groups = await List.castFrom(userDocSnapshot.data['groups']);

it shows an error: Unhandled Exception: type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'List'

This is the array in my Firestore:

What should I do?

Answer 1

You cannot directly turn a Map into a List. You would have to get to use forEach to split the map's key and values. Here is how you can get the Map's values and turn it into a List:

FirebaseDatabase.instance
    .reference()
    .child("users/$id")
    .once()
    .then((snapshot) {
  if (snapshot.value != null) {
    snapshot.value.forEach((k, v) {
      myList.add(v);
    });
  } else {
    print("value is null");
  }
});