SQLiteDatabase使用SELECT語句查詢數據庫時出現NullPointerException

Question

我試圖查詢我的數據庫以檢查匹配字段值是否存在。

非常多使用SELECT sql語句。

即使數據庫已經打開，當我試圖查詢數據庫時，出現NullPointerException錯誤。

下面的代碼是從類包含所有SQLite的方法：

public long createDBCard(String card_name, String card_type, String attributeType, 
      String summonRequirements, String card_description, 
      String spellSpeed, int levelStars, int rankStars, int atk_stat, int def_stat, 
      String setnumber, int cardNumberPass) 
    { 
     // TODO Auto-generated method stub 
     ContentValues cv = new ContentValues(); 

    String passedCardName = card_name; 
    //long l = Long.parseLong(passedCardName); 
    String returnedCardName = getCardName(passedCardName); 
    long numCards = Countcards(); 
    String numCardmsg = String.valueOf(numCards); 

    if (numCards == 51){ 
     Toast h1 = Toast.makeText(CarddbAdapter.this, "Error counting card records.", Toast.LENGTH_LONG); 
     h1.show(); 
    }else if(numCards == 0){ 
     Toast h = Toast.makeText(this, "No cards exists", Toast.LENGTH_LONG); 
     h.show(); 
    }else if(numCards >= 1){ 
     Toast b = Toast.makeText(CarddbAdapter.this, returnedCardName, Toast.LENGTH_SHORT); 
     b.show(); 
    }else{ 
     Toast b = Toast.makeText(CarddbAdapter.this, "FAIL!!!!!!!!!!!!!!!!!", Toast.LENGTH_SHORT); 
     b.show(); 
    } 

    cv.put(KEY_CARDNAME, card_name); 
    cv.put(KEY_CARDTYPE, card_type); 
    cv.put(KEY_ATTRIBUTETYPE, attributeType); 
    cv.put(KEY_SUMMONREQUIREMENTS, summonRequirements); 
    cv.put(KEY_CARD_DESCRIPTION, card_description); 
    cv.put(KEY_SPELLSPEED, spellSpeed); 
    cv.put(KEY_LEVELSTARS, levelStars); 
    cv.put(KEY_RANKSTARS, rankStars); 
    cv.put(KEY_ATK_STAT, atk_stat); 
    cv.put(KEY_DEF_STAT, def_stat); 
    cv.put(KEY_SETNUMBER, setnumber); 
    cv.put(KEY_CARDNUMBERPASS, cardNumberPass); 
    return ourDatabaseW.insert(DATABASE_TABLE_CARDS, null, cv); 
    //return 51; 
} 

public String getCardName(String passedName) throws SQLException{ 
     // TODO Auto-generated method stub 
     String[] columns = new String[]{ KEY_CARDNAME}; 
     Cursor c = ourDatabaseR.query(DATABASE_TABLE_CARDS, columns, KEY_CARDNAME + "='" + passedName + "'", null, null, null, null); 
     if (c != null){ 
      c.moveToFirst(); 
      String name = c.getString(0); 
      return name; 
     } 
     return "hello"; 
    } 

logcat的錯誤

05-11 01:15:49.456: E/AndroidRuntime(1509): FATAL EXCEPTION: main 
05-11 01:15:49.456: E/AndroidRuntime(1509): java.lang.RuntimeException: Unable to start activity ComponentInfo{cybertech.productions.yugiohlibrary/cybertech.productions.yugiohlibrary.LoadingScreen}: java.lang.NullPointerException 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.os.Handler.dispatchMessage(Handler.java:99) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.os.Looper.loop(Looper.java:123) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.app.ActivityThread.main(ActivityThread.java:3683) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at java.lang.reflect.Method.invoke(Method.java:507) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at dalvik.system.NativeStart.main(Native Method) 
05-11 01:15:49.456: E/AndroidRuntime(1509): Caused by: java.lang.NullPointerException 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.content.ContextWrapper.getResources(ContextWrapper.java:80) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.widget.Toast.<init>(Toast.java:89) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.widget.Toast.makeText(Toast.java:231) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at cybertech.productions.servicehelpers.CarddbAdapter.createDBCard(CarddbAdapter.java:144) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at cybertech.productions.yugiohlibrary.LoadingScreen.onCreate(LoadingScreen.java:37) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
05-11 01:15:49.456: E/AndroidRuntime(1509):  ... 11 more 

在我的活動之一，我使用這個類的一個對象調用createDBCard（ ） 方法。

任何幫助，將不勝感激。

我試着玩弄rawQuery（）方法，但有錯誤，哈哈。

Answer 1

我修復了它，現在到它返回我的查詢結果的位置。

調試別的東西與我怎麼設計我的open（）方法我發現後，我從嘗試不同的東西來解決一些先前的錯誤猜測，我宣佈上下文這個，而不是我預先定義私人final ourContext。

下面是第一個調試過的代碼，它用我的createDBCard（）方法解決了我以後的問題，即NullPointerException。

我宣佈我的private final ourContext後，我的open（）方法;前與我的其他變量的其餘部分DbHelper類：

的一個編碼如下錯誤：

public CarddbAdapter open() throws SQLException{ 
     ourHelper = new DbHelper(this); 
     ourDatabaseW = ourHelper.getWritableDatabase(); 
     ourDatabaseR = ourHelper.getReadableDatabase(); 
     return this; 
    } 

的一個正下方編碼：

public CarddbAdapter open() throws SQLException{ 
     ourHelper = new DbHelper(ourContext); 
     ourDatabaseW = ourHelper.getWritableDatabase(); 
     ourDatabaseR = ourHelper.getReadableDatabase(); 
     return this; 
    } 

正如你可以看到我改變ourHelper = new DbHelper（this）;至ourHelper = new DbHelper（ourContext）;

這樣做讓我意識到我需要改變所有的敬酒我createDBCard（）用我的預先定義的ourContext，而不是這個。

謝謝大家的幫助。