Why did my FirebaseReference object causes NullPointerException?

Question

So a bit of a heads up, I build a small Mobile Chat App for my task, everything works fine until I get NullPointerException when I do transition from my Contact List menu to the Chat menu... In the error I got this

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.bruh.chatapp, PID: 3797 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bruh.chatapp/com.bruh.chatapp.Obrol}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2193) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2243) at android.app.ActivityThread.access$800(ActivityThread.java:135) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:136) at android.app.ActivityThread.main(ActivityThread.java:5019) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at com.bruh.chatapp.Obrol.onCreate(Obrol.java:60) at android.app.Activity.performCreate(Activity.java:5231) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2157) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2243) at android.app.ActivityThread.access$800(ActivityThread.java:135) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:136) at android.app.ActivityThread.main(ActivityThread.java:5019) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) at dalvik.system.NativeStart.main(Native Method)

As you can see it's caused by a line in Obrol.java at line 60 which is containing

final DatabaseReference reference1 = firebaseDatabase.getReference("https://databaselink/Message/" + Pesan.Nama+"_"+Pesan.chatWith);

I also have tried change getReference() to getReferencefromUrl() but it stills returns NullPointerException

Then I tried to just make it as a comment to test if the reference1 object did causes this error, and it is, when I relaunch my app, and do transition from my Contact List menu to the Chat menu, it doesn't crash the app and also doesn't return NullPointerException error...

So I wonder why is this happening and how do I solve this error? Oh, here's my Firebase Database structure for additional reference

score 1 · Answer 1 · answered Mar 09 '20 at 14:26

1

Change this:

final DatabaseReference reference1 = firebaseDatabase.getReference("https://databaselink/Message/" + Pesan.Nama+"_"+Pesan.chatWith);

into this:

final DatabaseReference reference1 = firebaseDatabase.getReference().child("Users");

You don't have to add the URL of the database, the getReference() will return the root node of the database.

answered Mar 09 '20 at 14:26

Peter Haddad

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Yes, I get it that just using getReference will return to the root node, but how does this relate with the NullPointerException problem? – sterben Mar 09 '20 at 15:56
The variable reference1 is returning null, you shouldn't add `https://databaselink/Message/` in getReference... – Peter Haddad Mar 09 '20 at 16:11
So the link that caused reference1 returning null? – sterben Mar 09 '20 at 16:16
Yes you are referring to a node that doesn't exist thus you got null – Peter Haddad Mar 09 '20 at 19:04
But if you see the Database Structure above, you can see that I have a node named "Message", why my script don't detect that node? – sterben Mar 09 '20 at 22:03
again this whole reference is wrong `"https://databaselink/Message/" + Pesan.Nama+"_"+Pesan.chatWith`, where do you https in the database? – Peter Haddad Mar 09 '20 at 22:04
Well the https part is the real-time database link – sterben Mar 09 '20 at 22:18
but thats not how it works, you dont add the link to the database in your code... you just specify the node – Peter Haddad Mar 09 '20 at 22:18
Okay then, I'll work around with it – sterben Mar 09 '20 at 22:20

score 0 · Accepted Answer · answered Mar 09 '20 at 23:12

The reason you got this error is because your reference1 variable is returning null.

As for the cause, there are several possibilities (these are what I've encountered):

The node you referenced doesn't exist, so make sure that the node either root or child you referenced is exist in your database
You forgot to get Instance of your database, so make sure you indeed have getInstance in your Class before trying to get DatabaseReference to your class. To do getInstance you can use this code

final FirebaseDatabase database = FirebaseDatabase.getInstance();

reference: https://firebase.google.com/docs/database/admin/retrieve-data

Why did my FirebaseReference object causes NullPointerException?

2 Answers2