SQLiteDatabase使用SELECT语句查询数据库时出现NullPointerException

Question

我试图查询我的数据库以检查匹配字段值是否存在。

非常多使用SELECT sql语句。

即使数据库已经打开，当我试图查询数据库时，出现NullPointerException错误。

下面的代码是从类包含所有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的错误

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 

在我的活动之一，我使用这个类的一个对象调用createDBCard（ ） 方法。

任何帮助，将不胜感激。

我试着玩弄rawQuery（）方法，但有错误，哈哈。

Answer 1

我修复了它，现在到它返回我的查询结果的位置。

调试别的东西与我怎么设计我的open（）方法我发现后，我从尝试不同的东西来解决一些先前的错误猜测，我宣布上下文这个，而不是我预先定义私人final ourContext。

下面是第一个调试过的代码，它用我的createDBCard（）方法解决了我以后的问题，即NullPointerException。

我宣布我的private final ourContext后，我的open（）方法;前与我的其他变量的其余部分DbHelper类：

的一个编码如下错误：

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

的一个正下方编码：

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变ourHelper = new DbHelper（this）;至ourHelper = new DbHelper（ourContext）;

这样做让我意识到我需要改变所有的敬酒我createDBCard（）用我的预先定义的ourContext，而不是这个。

谢谢大家的帮助。