How To Retrieve A List From Firebase Avoid Asynchronous

I know that when we retrieve data from Firebase ,it will be asynchronous, so ussally i will put all the code inside addChildEventListener, like example i want to sort userList belo

Solution 1:

You currently use a ChildEventListener, which means your onChildAdded gets called for each child node immediately and then later whenever a new child is added. This indeed can be a lot of invocations.

If you use a ValueEventListener, its onDataChange will only be called once for the initial data (no matter how many child nodes there are), and then once for each change.

By adding a ValueEventListener to your current set up, you can keep things simple: add the child nodes to the lit like you're already doing, but only sort in onDataChange.

myRef.child("User").addValueEventListener(newValueEventListener() {
    @OverridepublicvoidonDataChange(DataSnapshot dataSnapshot) {
      sortUser(userList);
    }

    @OverridepublicvoidonCancelled(DatabaseError databaseError) {
        throw databaseError.toException();
    }
};

Firebase will only synchronize the data for the User node once, even when you have two listeners on it.

Solution 2:

You should probably retrieve the data sorted server side by using order-by methods and then listen to that one.

var userRef = firebase.database().ref('posts').orderByChild('Users');

If I guess correctly, you would not need separate sorting client side.

You can also filter data. Do refer the docs