wait until firebase retrieves data

Question

I want to build a method that returns a child value in FireBase. I tried to do something like this:

public String getMessage(){

           


        

Answer 1

As @CMikeB1 commented on another response in the java world when we are dealing with servlets and services rest we use sync calls to perform operations, it would be useful to have both options in sdk firebase admin so that the developer could choose which one to use depending on his case use.

I made my implementation from waiting to read the sync data using ApiFuture which is the current interface adopted by the sdk of the firebase admin. here's a link!

public DataSnapshot getMessage() {
    final SettableApiFuture<DataSnapshot> future = SettableApiFuture.create();
    databaseReference.child("MessagesOnLaunch").child("Message").addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            future.set(dataSnapshot);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            future.setException(databaseError.toException());
        }
    });
    try {
        return future.get();
    } catch(InterruptedException | ExecutionException e) {
        e.printStackTrace();
        return null;
    }
}

Answer 2

Add this code inside onDataChange() method

do{
    message = (String) dataSnapshot.getValue();
    if(message.equals(null)) 
        break;
}while (!message.equals(null));

                 

Answer 3

Make an interface

 public interface OnGetDataListener {
    //this is for callbacks
    void onSuccess(DataSnapshot dataSnapshot);
    void onStart();
    void onFailure();
}

Declare the following function readData()

public void readData(Firebase ref, final OnGetDataListener listener) {
    listener.onStart();
    ref.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            listener.onSuccess(dataSnapshot);
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {
            listener.onFailure();
        }
    });

}

Call the readData() function as follows

readData(root.child("MessagesOnLaunch").child("Message"), new OnGetDataListener() {
                @Override
                public void onSuccess(DataSnapshot dataSnapshot) {

               //got data from database....now you can use the retrieved data


                }
                @Override
                public void onStart() {
                    //when starting
                    Log.d("ONSTART", "Started");
                }

                @Override
                public void onFailure() {
                    Log.d("onFailure", "Failed");
                }
            });

readData() can be called inside your getMessage() method or even inside onCreate()