Android SQLite檢索整數

-2

如何從SQLite中的行中獲取單個值？例如我有getLevel（）方法和一個「id，coin，level」的行，getLevel（）用於獲取並返回levelonly。我怎樣才能做到這一點？這是我的代碼。Android SQLite檢索整數

public int getLevel(int id) { 
    int level = 0; 
    String selectQuery = "SELECT "+colCurrentLvl+" FROM " + userTable + " WHERE " +userID + "="+id; 

    SQLiteDatabase db = this.getReadableDatabase(); 
    Cursor cursor = db.rawQuery(selectQuery, null); 

    if (null != cursor && cursor.moveToFirst()) { 
     level = Integer.parseInt(cursor.getString(cursor.getColumnIndex(colCurrentLvl))); 
    } 

    cursor.close(); 
    db.close(); 

    return level; 
}

而在我的主類我需要設置它像這樣。

int level = db.getLevel(1);

但我的模擬器部隊關閉。任何幫助？

> 10-10 11:09:43.626: E/AndroidRuntime(856): FATAL EXCEPTION: main 
10-10 11:09:43.626: E/AndroidRuntime(856): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.androidexercises.pics1song/com.androidexercises.pics1song.Game}: java.lang.NullPointerException 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106) 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.app.ActivityThread.access$600(ActivityThread.java:141) 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.os.Handler.dispatchMessage(Handler.java:99) 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.os.Looper.loop(Looper.java:137) 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.app.ActivityThread.main(ActivityThread.java:5041) 
10-10 11:09:43.626: E/AndroidRuntime(856): at java.lang.reflect.Method.invokeNative(Native Method) 
10-10 11:09:43.626: E/AndroidRuntime(856): at java.lang.reflect.Method.invoke(Method.java:511) 
10-10 11:09:43.626: E/AndroidRuntime(856): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
10-10 11:09:43.626: E/AndroidRuntime(856): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
10-10 11:09:43.626: E/AndroidRuntime(856): at dalvik.system.NativeStart.main(Native Method) 
10-10 11:09:43.626: E/AndroidRuntime(856): Caused by: java.lang.NullPointerException 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:229) 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224) 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:188) 
10-10 11:09:43.626: E/AndroidRuntime(856): at com.androidexercises.pics1song.DatabaseHelper.getLevel(DatabaseHelper.java:51) 
10-10 11:09:43.626: E/AndroidRuntime(856): at com.androidexercises.pics1song.Game.<init>(Game.java:39) 
10-10 11:09:43.626: E/AndroidRuntime(856): at java.lang.Class.newInstanceImpl(Native Method) 
10-10 11:09:43.626: E/AndroidRuntime(856): at java.lang.Class.newInstance(Class.java:1319) 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.app.Instrumentation.newActivity(Instrumentation.java:1054) 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)

這是我如何初始化數據庫和關卡。

public class Game extends Activity { 

DatabaseHelper db; 

    protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.game); 

      db = new DatabaseHelper(Game.this); 
    level = db.getLevel(1); 
    } 
}

哦，我不需要添加新的行。我只需要每次更新同一行。

來源

2013-10-10 jayyyyy

什麼是'colCurrentLvl'？ – lub0v

字符串包含我級別的列名稱。 – jayyyyy

要求發佈實際錯誤和堆棧跟蹤是否太多了？ – njzk2

你試過這個嗎？

level = cursor.getInt(cursor.getColumnIndex(colCurrentLvl));

來源

2013-10-10 10:50:35 Saran

儘管仍然沒有運氣。 – jayyyyy

10-10 11:09:43.626: E/AndroidRuntime(856): Caused by: java.lang.NullPointerException 
10-10 11:09:43.626: E/AndroidRuntime(856): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:229) 10-10 

... 

10-10 11:09:43.626: E/AndroidRuntime(856): at com.androidexercises.pics1song.Game.(Game.java:39) 
10-10 11:09:43.626: E/AndroidRuntime(856): at java.lang.Class.newInstanceImpl(Native Method) 
10-10 11:09:43.626: E/AndroidRuntime(856): at java.lang.Class.newInstance(Class.java:1319)

你試圖太早從初始化數據庫活動類的成員變量，例如在構造函數中。但是，您不能使用該活動作爲Context，直到onCreate()。將成員變量初始化移動到onCreate()。無論如何，活動不應該需要明確的構造函數。

來源

2013-10-10 11:22:18 laalto

感謝您的回覆。但仍然有力量關閉。 – jayyyyy

Android SQLite檢索整數

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