Detect UIScrollView Direction in making gallerry

I am createing dynamic gallery getting url from web services and display on UIScrollView using afnetworking. Its fine for me. But i am facing problem getting the image index on uiscrollview. coz due to requiedment we want to zoom image on uiscrollview using url (full). first all image display on uiscrollview in thum. i have used scrollViewDidEndDecelerating and scrollViewWillBeginDragging method but i faced one problem if i scroll image fastly then one time scrollViewDidEndDecelerating method called so my count vale increase or dicrease one value. and 2nd i used scrollViewDidScroll method but its giving last index value if i scroll right and in left give me 1st index value(0). so these method not work me. my code is -

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
   _lastContentOffset = scrollView.contentOffset.x;
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    if (_lastContentOffset < (int)scrollView.contentOffset.x){
        indexNumber= indexNumber+1;
        NSLog(@"DirectionRight(indexNumber) = %i",indexNumber);
        if (indexNumber == [arrayUrl  count])
            indexNumber = indexNumber-1;
    }
    else if (_lastContentOffset > (int)scrollView.contentOffset.x){
        indexNumber= indexNumber-1;
        NSLog(@"DirectionLeft(indexNumber) = %i",indexNumber);
        if (indexNumber <0)
            indexNumber = 0;
    }
}

Requiedment - right UINavigationbar button use for zoom image . so i am getting index value of image using direction and zoom image change thum url to full url . so please help me