Attempt to invoke interface method 'boolean android.database.Cursor.requery()' on a null object refe-优快云博客

本文链接：https://blog.youkuaiyun.com/Rodulf/article/details/50721605

这篇博客讨论了在Android应用中遇到的错误，即尝试在null对象上调用Cursor.requery()方法。错误出现在主线程中，具体堆栈跟踪指向ZygoteInit.main()。解决方案是确保在使用前正确初始化Cursor对象，例如通过调用db.query()方法进行初始化。

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02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: FATAL EXCEPTION: main
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: Process: com.qiushibaike.qiushibaike, PID: 8477
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: java.lang.IllegalStateException: Could not execute method of the activity
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.view.View$1.onClick(View.java:4012)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.view.View.performClick(View.java:4761)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.view.View$PerformClick.run(View.java:19767)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:739)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:95)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.os.Looper.loop(Looper.java:135)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5310)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: Caused by: java.lang.reflect.InvocationTargetException
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.view.View$1.onClick(View.java:4007)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.view.View.performClick(View.java:4761)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.view.View$PerformClick.run(View.java:19767)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:739)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:95)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.os.Looper.loop(Looper.java:135)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5310)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: Caused by: java.lang.NullPointerException:Attempt to invoke interface method 'boolean android.database.Cursor.requery()' on a null object reference
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at com.qiushibaike.qiushibaike.MainActivity.add(MainActivity.java:90)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at com.qiushibaike.qiushibaike.MainActivity.onMyButtonClick(MainActivity.java:68)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.view.View$1.onClick(View.java:4007)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.view.View.performClick(View.java:4761)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.view.View$PerformClick.run(View.java:19767)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:739)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:95)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.os.Looper.loop(Looper.java:135)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5310)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)

02-23 11:03:17.433 8477-8477/com.qiushibaike.qiushibaike E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)

原因: cursor 的变量没有初始化. 通过初始化就可以了,例如我的项目里面:

cursor = db.query(getNoteDao().getTablename(),getNoteDao().getAllColumns(),null,null,null,null,null);