android - Firebase retrieve data Null outside method

Question

I put the below method inside an onCreate(), when the app launch it will trigger this method. But when I try to to get mName outside the ValueEventListener(), it return null and the app crashed.

Anyone know why this issue happen?

 ValueEventListener postListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            UserDetails info = dataSnapshot.getValue(UserDetails.class);
            Log.d(TAG, String.valueOf(dataSnapshot));

            mName = info.getName();
            **Log.d(TAG, mName); // HERE GET THE NAME**

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Log.w(TAG, "getUser:onCancelled", databaseError.toException());
        }
    };
    mDatabase.child("Admin")
            .child("Info")
            .child(uid)
            .addValueEventListener(postListener);

    **Log.d(TAG, mName); // HERE GET NULL**

Answer 1

Waitting for answers