Flutter future function

Question

i am trying to get some data from firebase and than use that data to take other information. I am trying to do it using a future function. The problem is that everything works fine but the list comes out empty at the end and i dont know how to make it wait until the values have been added to the list and than appear. As you can see in this photo, the list comes out empty and than after print out the results and when you look in the code its vice versa. I tried some stuff using the await but with no success. https://gyazo.com/4dc9b3b4d459270c7c4bf146baa6ae25 What do you guys think?

Future <DataSnapshot> getData()async{
  List lists = [];
  await databaseReference.once().then((DataSnapshot snapshot) {
    
    Map < dynamic, dynamic > values = snapshot.value;
      values.forEach((key, values)async {
       
        await FirebaseDatabase.instance.reference().child("Users/" + values["UID"].toString() + "/Name").once().then((DataSnapshot snapshot) {
           
            lists.add(snapshot.value);
            print(snapshot.value);
         
          }); }, );
          
          }
          
          );

          print(lists);
}

please add the code directly inside your question instead of a screenshot, using ``` ``` — Antonin GAVREL, Feb 10 '21 at 19:49
To answer your question, it may be because you are using both await and then? Make a choice but don't use both! — Antonin GAVREL, Feb 10 '21 at 19:52

Antonin GAVREL · Answer 1 · 2021-02-10T22:11:59.493

0

You have to make a choice between using 'await' and 'then' keyword, using both is not recommended. See Async/Await/then in Dart/Flutter for detailed explanation about the difference.

Future <List<Map < dynamic, dynamic >>> getData() async {
  List<Map < dynamic, dynamic >> lists = [];
  DataSnapshot snapshot = await databaseReference.once();
  Map < dynamic, dynamic > values = snapshot.value;
  await values.forEach((key, values) async {
      DataSnapshot snapshotUser = await FirebaseDatabase.instance.reference().child("Users/" + values["UID"].toString() + "/Name").once();
      lists.add(snapshotUser.value);
      print(snapshotUser.value);
   }
   print(lists);
   return lists;
}

edited Feb 10 '21 at 22:11

answered Feb 10 '21 at 19:54

Antonin GAVREL

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so i should remove the avait? – Andrei Marin Feb 10 '21 at 19:57
yes try first by removing the await keyword, and if it doesnt work try with await and getting rid of then (you will have to put the result of await in a variable, like var mydata = await databaseReference... ), it will work for sure. – Antonin GAVREL Feb 10 '21 at 19:58
ok so i remove all the awaits and it doesnt work, so it must be from the than but i dont know what to put instead of it – Andrei Marin Feb 10 '21 at 20:00
i mean the parts after 'then' what do i do with them – Andrei Marin Feb 10 '21 at 20:05
I have updated my answer with await, give it a try – Antonin GAVREL Feb 10 '21 at 20:43
https://gyazo.com/338b6699dffa8d0682e85e6fe9aa142a any idea why i get this? – Andrei Marin Feb 10 '21 at 20:53
so it's a Map < dynamic, dynamic > and not a string, try again with Map < dynamic, dynamic > instead of String – Antonin GAVREL Feb 10 '21 at 21:22
it doesnt give an error now but unfortunately it's the same result... – Andrei Marin Feb 10 '21 at 21:25
list comes out first and than the names.. it is really frustrating – Andrei Marin Feb 10 '21 at 21:25
try with await before values.forEach – Antonin GAVREL Feb 10 '21 at 21:29
it has something to do with that for sure – Andrei Marin Feb 10 '21 at 21:31
i mean i need a way to wait for that foreach to end – Andrei Marin Feb 10 '21 at 21:33
potentially the program uses the first snapshot variable instead of snapshotUser, try with renaming the variable – Antonin GAVREL Feb 10 '21 at 22:12

Flutter future function

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