looping on firestore documents by id

Question

I have document in Firestore that has an array of string elements that should referenced to IDs of other documents as well .

so my scenario is to get array of saved IDs from my Firestore then create for loop on it and query on Firestore to get each documents that meets that ID .

but my problem is I'm try to put every result of query to new array but i get only first element

here is my fire-store like :

http://prntscr.com/mh4ldy

my code :

 void getCoursesDetails(ArrayList<String> openedCourses, MyCallback2 myCallback2){

    // Get full details of every course
 // openedCourses array  here has size of 5 
for (int i = 0; i < openedCourses.size(); i++) {

    DocumentReference docRef = db.collection("courses").document(openedCourses.get(i));

    docRef.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
        @Override
        public void onSuccess(DocumentSnapshot documentSnapshot) {

            if (documentSnapshot.exists()) {
                detailedCourses.add(documentSnapshot.toObject(Courses.class));
                myCallback2.onCallback(detailedCourses);

            }
        }
    });
}
// when put myCallback2.onCallback(detailedCourses); here i get array of zero cuz Firestore loads data asynchronously
}

So my Question is : how to make my array of detailedCourses to save every element that got from for loop round from firestore result ?