Detect scrollview at top or bottom

 Option 1 : 
 
 override func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        let offset:CGPoint = scrollView.contentOffset;
        let bounds:CGRect = scrollView.bounds;
        let size:CGSize = scrollView.contentSize;
        let inset:UIEdgeInsets = scrollView.contentInset;
        let y:CGFloat = offset.y + bounds.size.height - inset.bottom;
        let h:CGFloat = size.height;
        
        let reload_distance:CGFloat = 30;
        if(y < h + reload_distance) {
            print("At top : load older data")
        }
        if(y > h + reload_distance) {
            print("At bottom : load more(newer) data")
            
        }
    }

Reference : http://stackoverflow.com/a/17860149/3734028



Option 2 : 
-(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    // UITableView only moves in one direction, y axis
    CGFloat currentOffset = scrollView.contentOffset.y;
    CGFloat maximumOffset = scrollView.contentSize.height - scrollView.frame.size.height;
    
    if (maximumOffset - currentOffset <= 20.0) {
        [self getMessages];
    }
}