Firebase getInstance returns null

Question

I want to download data from firebase. and I used the method below to use it comfortably among the activities. In mDatabase I can view data being downloaded in debug mode, but I cannot transfer it to the code I want. The piece of code I gave below always looks null. I do not know how to do it...

Thank you.

Firebase Json;

 "server" : {
    "time" : {
      "Time" : 1617695199510
    }
  }

This;

mDatabase.child("/server/time/Time").addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    server serverTime = null;
                    for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                        serverTime = snapshot.getValue(server.class);
                    }
                    MyApplication.getInstance().setmServer(serverTime); // This code always returns null. 
//I'm trying to pass the firebase value here. I am trying to pass the value here to setmServer (MyApplication).
                }
    
                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {
                    hideProgressDialog();
                }
            });

MyApplication.java:

public server mServer = null;
private static MyApplication mInstance = null;

@Override
    public void onCreate() {
        super.onCreate();
        mInstance = this;
}
    public static MyApplication getInstance() {
        return mInstance;
    }

public server getmServer(){
        return mServer;
    }

    public void setmServer(server mserver){
        mServer = mserver;
    }

server.java:

@IgnoreExtraProperties
public class server {
    public long Time;

    public server(long Time) {
        this.Time = Time;

    }
}

Answer 1

There is no need for any ".getChildren()" call to loop through the "DataSnapshot" object. You can use either the "server" class for that, or a simpler way would be to get the data directly from the property using the following lines of code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference timeRef = rootRef.child("server/time/Time");
timeRef.get().addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
    @Override
    public void onComplete(@NonNull Task<DataSnapshot> task) {
        if (task.isSuccessful()) {
            long time = task.getResult().getValue(Long.class);
            Log.d(TAG, "time: " + time);
        } else {
            Log.d(TAG, task.getException().getMessage()); //Don't ignore potential errors!
        }
    }
});

The result in the logcat will be:

time: 1617695199510

Answer 2

Try this...

mDatabase.child("/server/time/Time").addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    long time = dataSnapshot.getValue(Long.class);
                    Log.d(TAG, "Time :- " + time);
                    MyApplication.getInstance().setmServer(new server(time));
                }
    
                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {
                    hideProgressDialog();
                }
            });

The result in logcat is..

Time :- 1617695199510