FutureBuilder with lists

user_13955154 0
Viewed 199

This is the future function I want to call:

Future<List<Marker>> getMarkers() async {
  List<Marker> markerTemp = [];
  List<String> friendsList = [];
  QuerySnapshot snapshot = FireStoreUtils.getFriendsList(current.userID);
  for (var doc in snapshot.docs) {
    friendsList.add(doc.reference.id);
  }
  for (var friend in friendsList) {
    DocumentSnapshot document = await locationRef.doc(friend).get();
    MarkerTemp.add(Marker(...))
  }
  return markerTemp;
}

Now I want it to be called in FutureBuilder widget to save the results in a variable called markerList that is useful for my view. How can I do?

flutter-layout dart flutter
2 Answers

Your future builder, when the future finishes in your case, returns a list of markers. Now to use that list, you don't have to store it again, it's already returned and stored in your snapshot in your future builder. You can validate this by printing the length of it:

if(snapshot.hasData) print(snapshot.data.length.toString());
user_135580350 
return FutureBuilder<List<Marker>>(
  future: getMarkers(),
  builder: (context, snapshot) {
    if (snapshot.connectionState != ConnectionState.done) {
      // async call has not finished
      return const Center(child: CircularProgressIndicator());
    }
    if (snapshot.hasError) {
      // getMarkers() throws an exception
      return Center(child: Text(snapshot.error.toString()));
    }
    if (!snapshot.hasData) {
      // getMarkers() returns null
      return const Center(child: Text("getMarkers() returns null!"));
    }
    markerList = snapshot.data as List<Marker>; // cast to List<Marker>
    return SomeWidget(); // use markerList in this Widget
  },
);
user_33656670
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