DBconnection连接不上

11-24 02:08:21.050: D/gralloc_goldfish(1394): Emulator without GPU emulation detected.
11-24 02:09:06.610: W/dalvikvm(1394): threadid=1: thread exiting with uncaught exception (group=0xb4a5bb90)
11-24 02:09:06.700: E/AndroidRuntime(1394): FATAL EXCEPTION: main
11-24 02:09:06.700: E/AndroidRuntime(1394): Process: ui.cqupt, PID: 1394
11-24 02:09:06.700: E/AndroidRuntime(1394): java.lang.NullPointerException
11-24 02:09:06.700: E/AndroidRuntime(1394):  at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at db.cquupt.DBconnection.getConnection(DBconnection.java:39)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at model.cqupt.BookList.getBookList(BookList.java:25)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at control.cqupt.Contol.addBook(Contol.java:8)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at ui.cqupt.InsertActivity$ButtonListener.onClick(InsertActivity.java:43)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at android.view.View.performClick(View.java:4424)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at android.view.View$PerformClick.run(View.java:18383)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at android.os.Handler.handleCallback(Handler.java:733)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at android.os.Handler.dispatchMessage(Handler.java:95)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at android.os.Looper.loop(Looper.java:137)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at android.app.ActivityThread.main(ActivityThread.java:4998)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at java.lang.reflect.Method.invokeNative(Native Method)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at java.lang.reflect.Method.invoke(Method.java:515)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at dalvik.system.NativeStart.main(Native Method)

以上为错误代码，感觉自己太蠢了，看了好久才看到，一直显示数据库无法连接，

11-24 02:09:06.700: E/AndroidRuntime(1394):  at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
11-24 02:09:06.700: E/AndroidRuntime(1394):  at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)

后来才发现，忘记在MainActivity中插入连接数据库代码了DBconnection.setContext(this.getApplicationContext())，。这就是新手啊，希望其他人不要范这种错误。