java SQLite高分，草率IndexOutofBounds Android

Question

我在下面的代码中评论了IOOF异常正在发生的两个点。通过测试，我确信db创建正确，并且我能够插入其中。我试着在测试后把所有的东西整合在一起，但现在它不起作用了。LogCat也在下面

数据库助手。爪哇

private static final String RANK = "_id"; 
private static final String SCORE = "score"; 
private static final String PERCENTAGE = "percentage";
private static final String SUM = "sum";

public long getScore(int rank) {
    Cursor c = db.rawQuery("SELECT " + SCORE + " FROM " + TABLE + " WHERE " + RANK + " = " + rank, null);
      c.moveToFirst();
    long i = c.getInt(c.getColumnIndex("SCORE") + 1);
    c.close();
    return i;
}

public int getPercentage(int rank) {
    Cursor c = db.rawQuery("SELECT " + PERCENTAGE + " FROM " + TABLE + " WHERE " + RANK + " = " + rank, null);
      c.moveToFirst();
    int i = c.getInt(c.getColumnIndex("PERCENTAGE") + 1);  //Line 56
    c.close();
    return i;
}

public void onCreate(SQLiteDatabase db) {
    db.execSQL("CREATE TABLE " + TABLE + " ("
        + RANK + " INTEGER PRIMARY KEY AUTOINCREMENT,"
        + SCORE + " LONG,"
        + PERCENTAGE + " INTEGER,"
        + SUM + " INTEGER"
        + ");");

高分。爪哇

onCreate(...) {

    r1p.setText("Row1 P: " + dh.getPercentage(1));  //Row 90
    r1s.setText("Row1 S: " + dh.getScore(1));

    r2p.setText("Row2 P: " + dh.getPercentage(2));
    r2s.setText("Row2 S: " + dh.getScore(2));

    r3p.setText("Row3 P: " + dh.getPercentage(3));
    r3s.setText("Row3 S: " + dh.getScore(3));

    //etc...

LogCat输出

01-04 00:30:28.462: E/AndroidRuntime(5440): FATAL EXCEPTION: main
01-04 00:30:28.462: E/AndroidRuntime(5440): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.Highscores}: 安卓.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.app.ActivityThread.access$600(ActivityThread.java:141)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.os.Handler.dispatchMessage(Handler.java:99)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.os.Looper.loop(Looper.java:137)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.app.ActivityThread.main(ActivityThread.java:5039)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at java.lang.reflect.Method.invokeNative(Native Method)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at java.lang.reflect.Method.invoke(Method.java:511)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:560)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at dalvik.system.NativeStart.main(Native Method)
01-04 00:30:28.462: E/AndroidRuntime(5440): Caused by: 安卓.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.database.AbstractCursor.checkPosition(AbstractCursor.java:424)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:136)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.database.AbstractWindowedCursor.getInt(AbstractWindowedCursor.java:68)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at com.example.test.DatabaseHelper.getPercentage(DatabaseHelper.java:58)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at com.example.test.Highscores.onCreate(Highscores.java:90)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.app.Activity.performCreate(Activity.java:5104)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
01-04 00:30:28.462: E/AndroidRuntime(5440):     at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
01-04 00:30:28.462: E/AndroidRuntime(5440):     ... 11 more

编辑：我整合了建议，现在错误在同一行，但我认为略有不同。我更新了上面的LogCat输出

Answer 1

你需要先打电话给moveToFirst()，然后再开始Cursor

  Cursor c = db.rawQuery("SELECT " + SCORE + " FROM " + TABLE + " WHERE " + RANK + " = " + rank, null);
    c.moveToFirst();
    //It is always better to do hasNext() check here. Just to make sure rows are available otherwise it may throw exception.
    long i = c.getInt(c.getColumnIndex("SCORE") + 1);

有关如何使用游标，请参见本example