帮助光标android问题！

我尝试通过使用方法来测试数据库中的记录是否存在。帮助光标android问题！

public boolean Exists(/*String _id*/) { 
    Cursor cursor = mDb.rawQuery("select * from "+ TABLE_USER, null); 
    boolean exists = (cursor.getCount() > 0); 
    cursor.close(); 
    return exists; 
}

然后我把它称为

if (Exists()) // do sth;

但它强制关闭时，我跑了！

这里我的日志猫：

07-13 15:06:55.961: ERROR/AndroidRuntime(1407): FATAL EXCEPTION: main 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407): java.lang.RuntimeException: Unable to start activity ComponentInfo{project.bm/project.bm.GPSTracerActivity}: java.lang.NullPointerException 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1622) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1638) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:928) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at android.os.Handler.dispatchMessage(Handler.java:99) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at android.os.Looper.loop(Looper.java:123) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at android.app.ActivityThread.main(ActivityThread.java:3647) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at java.lang.reflect.Method.invokeNative(Native Method) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at java.lang.reflect.Method.invoke(Method.java:507) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at dalvik.system.NativeStart.main(Native Method) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407): Caused by: java.lang.NullPointerException 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at project.bm.GPSTracerActivity.Exists(GPSTracerActivity.java:145) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at project.bm.GPSTracerActivity.onCreate(GPSTracerActivity.java:47) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1586) 
07-13 15:06:55.961: ERROR/AndroidRuntime(1407):  ... 11 more

来源

2011-07-13 sayvortana

尽管没有获得足够的信息，可能'mDb'在这一点上是空的？ – MByD

标记NPE线。 –

我将其声明为全局私有SQLiteBuilder mDb; 和我已经添加mDb =新 – sayvortana

见你没与MDB打开数据库object.First打开数据库，然后运行query.Also放在try/catch语句block.Otherwise光标相关的代码你会接近力量。

来源

2011-07-13 08:22:49 Rasel

thx它解决了 – sayvortana

帮助光标android问题！

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