Android 使用sqlite登录时出现java.lang.NullPointerException

我正试图使用

电话号码

和

密码

登录，但当我使用此功能时，它会发出

NullPointerException

：

Cursor cursor=db.query("CitizenDetails", null, "phone=?", new String[]{phone}, null, null, null);

哪里出了问题？几个小时来我一直在想这个问题，谢谢

日志：

02-27 12:10:58.783: E/AndroidRuntime(6586): FATAL EXCEPTION: main
02-27 12:10:58.783: E/AndroidRuntime(6586): java.lang.NullPointerException
02-27 12:10:58.783: E/AndroidRuntime(6586):     at com.example.customdialogregistration.DatabaseHelper.getSinlgeEntry(DatabaseHelper.java:200)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at com.example.customdialogregistration.MainActivity$1$1.onClick(MainActivity.java:75)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at android.view.View.performClick(View.java:4204)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at android.view.View$PerformClick.run(View.java:17355)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at android.os.Handler.handleCallback(Handler.java:725)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at android.os.Handler.dispatchMessage(Handler.java:92)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at android.os.Looper.loop(Looper.java:137)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at android.app.ActivityThread.main(ActivityThread.java:5041)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at java.lang.reflect.Method.invokeNative(Native Method)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at java.lang.reflect.Method.invoke(Method.java:511)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
02-27 12:10:58.783: E/AndroidRuntime(6586):     at dalvik.system.NativeStart.main(Native Method)

---

只有当

db

为

null

时，该行才能NPE。您之前是否初始化过此行

SQLiteDatabase db = this.getWritableDatabase();