java - 游标 while 循环返回除最后一个值之外的每个值

Question

我正在使用 while 循环遍历游标，然后输出数据库中每个点的经度和纬度值。

出于某种原因，它没有返回光标中的最后一组(或第一个取决于我是否使用 Cursor.MoveToLast)经度和纬度值。

这是我的代码:

public void loadTrack() {
SQLiteDatabase db1 = waypoints.getWritableDatabase();
Cursor trackCursor = db1.query(TABLE_NAME, FROM, "trackidfk=1", null, null, null,ORDER_BY); 

    trackCursor.moveToFirst();
    while (trackCursor.moveToNext()) {
        Double lat = trackCursor.getDouble(2);
        Double lon = trackCursor.getDouble(1);
        //overlay.addGeoPoint( new GeoPoint( (int)(lat*1E6),  (int)(lon*1E6)));
        System.out.println(lon);
        System.out.println(lat);
    }
}

由此我得到:

*******************************************
04-02 15:39:07.416: INFO/System.out(10551): 3.0
04-02 15:39:07.416: INFO/System.out(10551): 5.0
04-02 15:39:07.416: INFO/System.out(10551): 4.0
04-02 15:39:07.416: INFO/System.out(10551): 5.0
04-02 15:39:07.416: INFO/System.out(10551): 5.0
04-02 15:39:07.416: INFO/System.out(10551): 5.0
04-02 15:39:07.416: INFO/System.out(10551): 4.0
04-02 15:39:07.416: INFO/System.out(10551): 4.0
04-02 15:39:07.416: INFO/System.out(10551): 3.0
04-02 15:39:07.416: INFO/System.out(10551): 3.0
04-02 15:39:07.416: INFO/System.out(10551): 2.0
04-02 15:39:07.416: INFO/System.out(10551): 2.0
04-02 15:39:07.493: INFO/System.out(10551): 1.0
04-02 15:39:07.493: INFO/System.out(10551): 1.0
***************************************************************
7 Sets of values, where I should be getting 8 sets.

谢谢。

Answer 1

moveToNext() 有两个特点。它返回一个 boolean 值，表示是下一个，但同时它继续前进并移动光标。

public void loadTrack() {
SQLiteDatabase db1 = waypoints.getWritableDatabase();
Cursor trackCursor = db1.query(TABLE_NAME, FROM, "trackidfk=1", null, null, null,ORDER_BY); 

    trackCursor.moveToFirst();
    do {
        Double lat = trackCursor.getDouble(2);
        Double lon = trackCursor.getDouble(1);
        //overlay.addGeoPoint( new GeoPoint( (int)(lat*1E6),  (int)(lon*1E6)));
        System.out.println(lon);
        System.out.println(lat);
    } while (trackCursor.moveToNext());
}