我正在處理一個需要數據庫的android項目。我遇到的問題是當我啓動它時,出現nullpointerexception錯誤。通過logcat,我縮小了範圍,到了數據庫更新的時候,並試圖打開。這是正常的,還是我看起來很麻煩?
logcat的:android sqlite nullpointer錯誤
02-12 15:41:33.810: ERROR/AndroidRuntime(354): java.lang.RuntimeException: Unable to start activity ComponentInfo{arch.field/arch.field.ChooseSite}: java.lang.NullPointerException
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at android.os.Handler.dispatchMessage(Handler.java:99)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at android.os.Looper.loop(Looper.java:123)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at android.app.ActivityThread.main(ActivityThread.java:3683)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at java.lang.reflect.Method.invokeNative(Native Method)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at java.lang.reflect.Method.invoke(Method.java:507)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at dalvik.system.NativeStart.main(Native Method)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): Caused by: java.lang.NullPointerException
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at arch.field.BmDb$DatabaseHelper.onUpgrade(BmDb.java:96)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:132)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at arch.field.BmDb.open(BmDb.java:110)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at arch.field.ChooseSite.onCreate(ChooseSite.java:30)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
02-12 15:41:33.810: ERROR/AndroidRuntime(354): ... 11 more
OnUpgrade代碼:
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2)
{
Log.d("MonkeyDatabase","DbUpdater");
db.execSQL("Drop table if exists "+TABLE_SITE_NAME);
db.execSQL("Drop table if exists "+TABLE_UNIT_NAME);
db.execSQL("Drop table if exists "+TABLE_BONESHELL_NAME);
db.execSQL("Drop table if exists "+TABLE_CERAMIC_NAME);
db.execSQL("Drop table if exists "+TABLE_LITHIC_NAME);
onCreate(db);
}
開放代碼:
public BmDb open() throws SQLException
{
Log.d("Database","open");
db= BmDb.getWritableDatabase();
return this;
}
更多的代碼:
public BmDb(Context context)
{
this.context= context;
BmDb= new DatabaseHelper(context);
}
public static class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context){
super(context, DATABASE_NAME, null, VERSION);
}
這是來自ChooseSite代碼文件(帶行號):
final BmDb db=new BmDb(this);
db.open(); **this is the line mentioned in my logcat**
final Cursor c= db.GetSite();
if (c.moveToFirst()){
do{
sites(c);
}while (c.moveToNext());
}
對我在看什麼有什麼建議嗎?
爲什麼這會幫助糾正它?它的工作,但剛剛經歷了另一個錯誤,那人會與我的GetSite代碼,這就是: 公共光標GetSite() \t { \t \t回db.query(TABLE_SITE_NAME,新的String [] {KEY_SITEID, KEY_SITENAME,KEY_SITELOC},null,null,null,null,null); \t} 我是使用SQLite與android的新手,但從我發現的所有教程中,這是常見的形式。我標記錯了嗎? – 2012-02-13 04:33:19
看着android開發人員網站,我發現了遊標查詢的兩個實例。公共遊標查詢(SQLiteDatabase db,String [] projectionIn,String selection,String [] selectionArgs,String groupBy,String having, String sortOrder) 據我所知,我正確地遵循它。有什麼我缺少的東西嗎? – 2012-02-13 04:54:48
好吧,我感覺很蠢。爲什麼try {} catch(){}語句使所有不同?這也解決了我剛剛評論過的其他問題。我還發現,我只需要在try {} catch {}中調用db.open()一次。 – 2012-02-13 05:11:06