Android Firebase addListenerForSingleValueEvent is not working

Question

I know this has been asked a lot but I still can get it to work. Here's my code:

private int test;

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference userRef = rootRef.child("Users");

test = 0;
userRef.addListenerForSingleValueEvent(new ValueEventListener() {
   @Override
   public void onDataChange(DataSnapshot dataSnapshot) {
        if (dataSnapshot.hasChild(userID))
            test = 1;
        else
            test = 2;
   }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

Log.d(TAG, "Test = " + test);

Here's what on Firebase:

• appname-e545e
  • Users
    • userID

I don't know why but the variable "test" always return value 0, which means addListenerForSingleValueEvent didn't work. Thanks for helping in advanced

Answer 1

The data is loaded from Firebase asynchronously. By the time your log test, the onDataChange hasn't run yet.

To see this in action, add some more logging inside onDataChange:

private int test;

test = 0;
userRef.addListenerForSingleValueEvent(new ValueEventListener() {
   @Override
   public void onDataChange(DataSnapshot dataSnapshot) {
        if (dataSnapshot.hasChild(userID)) {
            test = 1;
        }
        else {
            test = 2;
        }
        Log.d(TAG, "Test2 = " + test);
   }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        throw databaseError.toException(); // Don't ignore errors
    }
});

Log.d(TAG, "Test = " + test);

Now you'll first see:

Test = 0

And then once the data has loaded and onDataChange gets called:

Test = 1

or

Test = 2

For this reason you should always put (or call) the code that needs the data from the database from within onDataChange().