-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
//当scrollview中content的竖直位移加上scrollView的高度大于等于content的总高度时，表示用户划到scrollview的底端
if ((scrollView.contentOffset.y + scrollView.frame.size.height) >= scrollView.contentSize.height)
{
//do something，like "loading more"
}
}