Firebase Checking if username exists

Question

I am currently developing an android app that only requires the user to sign up once after pressing start. The next time the user opens the application, pressing start will redirect the user to the main game already.

I was able to do this using SharedPreferences. After signing up, I store a value called currentState and I use it to check if the user has already signed up. Here's the code:

   final int currentState = sharedPreferences.getInt(USERSTATE_NUM_KEY,0);
   if(currentState == 0 ) {
          Intent i = new Intent(MainActivity.this, Main_Screen.class);
          startActivity(i);
    } else{
               // Redirect user to tutorial page, then the map page.
    }

Now I was asked to accomplish this again using Firebase since I've already stored the user data.

Here's my code so far just to try if it's going to the onDataChange but it doesn't and I'm not sure how to do it now. Here's my code so far:

final String currentUsername = sharedPreferences.getString(USERNAME_NUM_KEY, "");
final DatabaseReference userNameRef = rootReference.child("users");
startGame.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            userNameRef.orderByChild("username").equalTo(currentUsername)
                    .addListenerForSingleValueEvent(new ValueEventListener() {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot) {
                            if(dataSnapshot.exists()){
                                Log.v("TESTERR", "HELLO I EXIST LOL");
                            }
                            else{
                                Log.v("TESTERR", "NEW USER PAGE");
                            }
                        }

                        @Override
                        public void onCancelled(DatabaseError databaseError) {

                        }
                    });
 }
 });

Thank you!!!

We have an Android project that requires us to use Services. My group mate told me to do it again to further utilize the database because we're just using it now for our leaderboard page. — Alex Espiritu
– Alex Espiritu, Commented Apr 3, 2018 at 12:06
but why do you want to use ondatachange to check if user is logged in? Have you used firebase authentication? — Peter Haddad
– Peter Haddad, Commented Apr 3, 2018 at 12:20
actually i was just searching for how to actually check if the user already exists when the application starts. what i really need is just to check if its in the database but the only answer i could find was the one above — Alex Espiritu
– Alex Espiritu, Commented Apr 3, 2018 at 12:27
with the new code, everytime i click start i dont think im getting the snapshot. im new to firebase and im not sure why the "datasnapshot.exists" is inside ondatachanged thats why i was trying to see if it was going to go through the method — Alex Espiritu
– Alex Espiritu, Commented Apr 3, 2018 at 12:33

Peter Haddad · Accepted Answer · 2018-04-03 12:38:40Z

5

This:

userNameRef.orderByChild("username").equalTo(currentUsername)

is a query it is like saying where username= currentUsername

The currentUsername is the logged in user, the datasnapshot is users.

So in your database you have:

users
 userid
   username: currentUsername

When you use if(dataSnapshot.exists()){ it checks the snapshot which is users and checks the where condition, if theys exists in the database then it will enter the if clause.

If the where condition does not exists in the database then it will enter the else.

answered Apr 3, 2018 at 12:38

Peter Haddad

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2 Comments

Alex Espiritu Over a year ago

It's weird though because nothing shows up on my Log making me think that it doesn't really enter the method at all?

Peter Haddad Over a year ago

check if it is "users" and not "Users", also inside the equalTo write the name: "kanyewest" as in the database and test it

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