CODEWITHSUNDEEP
androidfirebase
pileup
pileup

Reputation: 3262

Why is my path to value wrong - I get null

I have the following data base:

database
    |
    places
       |  
       |____user1
       |      |_____outside: "yes"
       |
       |____user2
              |_____outside: "no"

I am fetching the data like that:

mDatabaseReference = FirebaseDatabase.getInstance().getReference("places");

ValueEventListener placesListener = new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {                
                for(DataSnapshot datas: dataSnapshot.getChildren()){
                    //this won't work
                    String place = datas.child("user1").child("outside").getValue().toString();

            }
mDatabaseReference.addValueEventListener(placesListener);

But it doesn't work, when I launch my app, I get that it is a null and the app crashes.

Log crash, as requested:

Process: com.example.places, PID: 32431
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
    at com.example.places.MainActivity$1.onDataChange(MainActivity.java:44)
    at com.google.firebase.database.obfuscated.zzap.zza(com.google.firebase:firebase-database@@16.0.3:75)
    at com.google.firebase.database.obfuscated.zzca.zza(com.google.firebase:firebase-database@@16.0.3:63)
    at com.google.firebase.database.obfuscated.zzcd$1.run(com.google.firebase:firebase-database@@16.0.3:55)
    at android.os.Handler.handleCallback(Handler.java:789)
    at android.os.Handler.dispatchMessage(Handler.java:98)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6944)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)

Upvotes: 0

Views: 44

Answers (1)

Martin Lund
Martin Lund

Reputation: 1169

dataSnapshot.getChildren() currently iterates over all children in your "places"

Currently you have user1 and user2.

When you iterate over them in a for loop like you are doing

String place = datas.child("user1").child("outside").getValue().toString();

You will eventually try to look for datas.child("user1") when it does not exist.

in the for loop you can use 

datas.child("outside").getValue().toString();

If you log this you will find first user1 outside value printed, and then user2.

If you need user1 you can add an if statement where you check the key

if(datas.getKey().toString().equals("user1"))

Then do what you need. user1 should not be hardcoded, but a parameter that fetches the user you need.

Upvotes: 1

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