-(void)scrollViewWillBeginDragging:(UIScrollView*)scrollView{
lastContentOffset = scrollView.contentOffset.y;
}
-( void )scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
if (scrollView.contentOffset.y > lastContentOffset && scrollView.contentOffset.y >= 40)
{
//向上
// topIV.hidden = YES;
NSLog(@"向上");
[UIView animateWithDuration:0.1f animations:^{
topIV.alpha = .0f;
}];
} else if (scrollView. contentOffset.y
