Assigned value in inner class not assigned correctly

Question

I have this function to return number of nodes at a firestore endpoint but it seems not to ork as expected. Currently, the number of nodes at the endpoint is 1.Here is the function

public static int getInvoicesCount(String uid)
{
    final int[] count = new int[1];

    FirebaseFirestore firestore;
    firestore = FirebaseFirestore.getInstance();

    CollectionReference invoicesRef = firestore
            .collection("invoices");

    Query query = invoicesRef.whereEqualTo("creator_id",uid);

    Task<QuerySnapshot> task = query.get();


    task.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        @Override
        public void onComplete(@NonNull Task<QuerySnapshot> task) {
            if(task.isSuccessful())
            {
                if(task.getResult().isEmpty())
                {
                    count[0] = 0;
                    Log.d("counter",String.valueOf(count[0]));
                }
                else {
                    Log.d("counter is",String.valueOf(task.getResult().size()));
                    count[0] = task.getResult().size();
                }

            }
        }
    });

    return count[0];

}

Logging the value of count[0] in the else statement gives 1 but the return value at the end of the function is still giving 0 instead of 1;

Answer 1

The code you have in onComplete method is invoked a lot after your method is returning, when your task is completed. In your code you are just attaching the listener, it can be called a lot later or even never at all.

You have a lot of options, for example Future , or attaching a callback to your listener (so listener calls the callback after it completes).

task.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<QuerySnapshot> task) {
        if(task.isSuccessful())
        {
            if(task.getResult().isEmpty())
            {
                count[0] = 0;
                Log.d("counter",String.valueOf(count[0]));
            }
            else {
                Log.d("counter is",String.valueOf(task.getResult().size()));
                count[0] = task.getResult().size();
            }

            methodWhenListenerCompletes(count[0]);
        }
    }
});
...
public void methodWhenListenerCompletes(int count) {
  // do something
}