Cursor while loop returning every value but the last

问题

I am using a while loop to iterate through a cursor and then outputing the longitude and latitude values of every point within the database.

For some reason it is not returning the last (or first depending on if I use Cursor.MoveToLast) set of longitude and latitude values in the cursor.

Here is my code:

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);
    }
}

From this I am getting:

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.

Thanks.

回答1:

moveToNext() has two features. It returns a boolean signifying that there is a next, but at the same time it goes ahead and moves the cursor.

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());
}

回答2:

Cursor c=null;
c=......;
try {
    if (c!=null) {
        for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {

        }

    }
} finally {
    if (c!=null) {
        c.close();
    }
}

回答3:

Your skipping the first value actually, not the last.

trackCursor.moveToFirst();
while (trackCursor.moveToNext()) {

The first time into the while loop you are pointing at the 2nd row.

I would convert your while loop to a do-while loop

回答4:

You just executed the query. Can't you just get rid of the moveToFirst()?

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

    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);
    }
}

来源：https://stackoverflow.com/questions/2567594/cursor-while-loop-returning-every-value-but-the-last

标签

java

sql

android

sqlite

cursor