Question

当我使用以下代码...并按下应用程序中的删除按钮时，该值将在firebase数据库中删除，但会导致我的应用程序崩溃。

    mSingleRemoveBtn.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View view)
            {
                if(mPostKey!=null)
                {
                    System.out.println("The key is " + mPostKey);

                    mDatabase.child(mPostKey).removeValue();
                    Intent mainIntent = new Intent(BlogSingleActivity.this, MainActivity.class);
startActivity(mainIntent);

                }
                else
                {
                    System.out.println("The key is empty");
                }

            }

当我删除＆＃34; mDatabase.child（mPostKey）.removeValue（）;＆＃34; 时，该应用程序运行正常，但显然没有从我的数据库中删除该条目。

logcat的

    08-01 19:42:51.093 32536-32536/com.vks_apps.blogs I/System.out: The key is -KqT82kPqOE_iq0UKHnm

                                                                --------- beginning of system
08-01 19:42:51.129 32536-4494/com.vks_apps.blogs V/FA: Inactivity, disconnecting from the service
08-01 19:42:51.131 32536-32536/com.vks_apps.blogs D/AndroidRuntime: Shutting down VM
08-01 19:42:51.132 32536-32536/com.vks_apps.blogs E/UncaughtException: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
                                                                           at com.google.firebase.database.DatabaseReference.child(Unknown Source)
                                                                           at com.vks_apps.blogs.BlogSingleActivity$1.onDataChange(BlogSingleActivity.java:88)
                                                                           at com.google.android.gms.internal.zzbmz.zza(Unknown Source)
                                                                           at com.google.android.gms.internal.zzbnz.zzYj(Unknown Source)
                                                                           at com.google.android.gms.internal.zzboc$1.run(Unknown Source)
                                                                           at android.os.Handler.handleCallback(Handler.java:751)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                           at android.os.Looper.loop(Looper.java:154)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:6077)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
08-01 19:42:51.135 32536-4494/com.vks_apps.blogs D/FA: Logging event (FE): _ae, Bundle[{_o=crash, _sc=BlogSingleActivity, _si=-4635728123048285128, timestamp=1501596771132, fatal=1}]
08-01 19:42:51.157 32536-4494/com.vks_apps.blogs V/FA: Using measurement service
08-01 19:42:51.157 32536-4494/com.vks_apps.blogs V/FA: Connecting to remote service

                                                       --------- beginning of crash
08-01 19:42:51.378 32536-32536/com.vks_apps.blogs E/AndroidRuntime: FATAL EXCEPTION: main
                                                                    Process: com.vks_apps.blogs, PID: 32536
                                                                    java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
                                                                        at com.google.firebase.database.DatabaseReference.child(Unknown Source)
                                                                        at com.vks_apps.blogs.BlogSingleActivity$1.onDataChange(BlogSingleActivity.java:88)
                                                                        at com.google.android.gms.internal.zzbmz.zza(Unknown Source)
                                                                        at com.google.android.gms.internal.zzbnz.zzYj(Unknown Source)
                                                                        at com.google.android.gms.internal.zzboc$1.run(Unknown Source)
                                                                        at android.os.Handler.handleCallback(Handler.java:751)
                                                                        at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                        at android.os.Looper.loop(Looper.java:154)
                                                                        at android.app.ActivityThread.main(ActivityThread.java:6077)
                                                                        at java.lang.reflect.Method.invoke(Native Method)
                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
08-01 19:42:51.445 32536-5218/com.vks_apps.blogs I/FirebaseCrash: Sending crashes
08-01 19:42:52.021 32536-5218/com.vks_apps.blogs I/FirebaseCrash: Response code: 200
08-01 19:42:52.023 32536-5218/com.vks_apps.blogs I/FirebaseCrash: Report sent with crash report id: 6e22679504000000

Answer 1

当您使用logcat sais Can't pass null for argument 'pathString' in child()时，这意味着此代码行中的某些内容为null：

mDatabase.child(mPostKey).removeValue();

唯一可以为null的是mPostKey。在使用nullity方法之前检查removeValue()。

if(mPostKey != null) {
    mDatabase.child(mPostKey).removeValue();
}

要从Firebase数据库中删除记录，请确保mPostKey不为空。看看哪里变成了空。

查看logcat mPostKey中显示-KqT82kPqOE_iq0UKHnm的更新问题，BlogSingleActivity中第88行发生的错误是问题所在。问题实际上是在第88行，再次使用mPostKey导致应用程序崩溃，因为将空值传递给child()方法。添加mPostKey != null仅用于检查无效。

希望它有所帮助。

Answer 2

在callstack中，您可以看到问题出在BlogSingleActivity$1.onDataChange()中。在那里，您正在调用数据库并将空值传递给child()。

使用removeValue（）时Firebase应用崩溃

2 个答案: