如何修复 Null 指针异常 Firebase Auth

Question

I am trying to Retrieve and display the user name from the current authenticated user with FirebaseAuth but the app crash with a NullPointerException

I tryed to display the the user.getDisplayName() in the consol and its not Null

ImageView profilePicView = findViewById(R.id.profile_pic);
        TextView nameView = findViewById(R.id.name);
        TextView emailView = findViewById(R.id.email);

        FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
        if (user != null) {
            if (user.getDisplayName() != null) {
                System.out.println("------------------------------user display name : " + user.getDisplayName());
                nameView.setText(user.getDisplayName());
            }

            if (user.getEmail() != null) {
                emailView.setText(user.getEmail());
            }

            if (user.getPhotoUrl() != null) {
                Glide.with(this)
                        .load(user.getPhotoUrl())
                        .into(profilePicView);
            }
        }

Here is the stack Error

I/System.out: ------------------------------user display name : Mohammed Elmahdi Bechlaghem
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.megadevbrain.ranahna, PID: 20913
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.megadevbrain.ranahna/com.megadevbrain.ranahna.Navigation}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3121)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3264)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1955)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7076)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
        at com.megadevbrain.ranahna.Navigation.onCreate(Navigation.java:52)
        at android.app.Activity.performCreate(Activity.java:7327)
        at android.app.Activity.performCreate(Activity.java:7318)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1275)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3101)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3264) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1955) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7076) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965) 
I/Process: Sending signal. PID: 20913 SIG: 9
Process 20913 terminated.

Answer 1

Null pointer try to say that your Textview is null. That can happen because the findviewbyid is not matching with the right one on your XML. Be sure your id matches your XML and the.Java java file

Answer 2

you must use Thread in your method that calls the object.

Answer 3

Either 'nameView' or 'emailView' variable is null. Please check R.id.name and R.id.email are valid TextView in current view xml.