如何修復 Null 指針異常 Firebase Auth

Question

我正在嘗試使用 FirebaseAuth 從當前經過身份驗證的用戶中檢索並顯示用戶名，但應用程序崩潰並出現 NullPointerException

我試圖在控制台中顯示 user.getDisplayName() 而不是 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);
            }
        }

這是堆棧錯誤

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 指針嘗試說您的 Textview 是 null。 這可能是因為 findviewbyid 與 XML 上的正確的不匹配。 確保您的 id 與您的 XML 和 .Java java 文件匹配

Answer 2

您必須在調用 object 的方法中使用 Thread。

Answer 3

“nameView”或“emailView”變量是 null。 Please check R.id.name and R.id.email are valid TextView in current view xml.