尝试在 android studio firebase mainactivity 中的空对象引用上调用虚方法 boolean java.lang.String.equals(java.lang.Object)

Question

I am making a chatting application in which when I login, I get this error in Logcat and my app crashes.

2022-03-12 16:09:44.805 22115-22115/com.dccodes.chugli E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.dccodes.chugli, PID: 22115
    java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
        at com.dccodes.chugli.MainActivity$2.onDataChange(MainActivity.java:91)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75)
        at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:201)
        at android.app.ActivityThread.main(ActivityThread.java:6810)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)

I don't understand why I get this error, I used firebase for my app. My main activity is very large, so I uploaded the photo of code.

I don't understand why I get this error.

Answer 1

Try using addListenerForSingleValueEvent(new ValueEventListener() { instead of ValueEventListener Because ValueEventListener is triggered everytime that you have a change in 'reference' tree, if nothing happens it won't be triggered, and this block of code won't run.

However addListenerForSingleValueEvent runs this block of code one time no matter what.

Also check that 'refernece' is pointing to the exact place in your Firebase that you want to listen to. And if it's right check that the user it's pointing to isn't null.