scrollView的代理方法

//scrollView 正在滚动的时候调用  偏移量一直变化
- (void)scrollViewDidScroll:(UIScrollView *)scrollView;

// scrollView正在缩放
 - (void)scrollViewDidZoom:(UIScrollView *)scrollView

// 开始拖拽的时候调用
 - (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView;

//即将停止拖拽的时候调用
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset NS_AVAILABLE_IOS(5_0);

//已经停止拖拽调用
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate;

// scrollView即将开始减速
- (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView;

// scrollView 停止减速  停止
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView;

//scrollView 停止滚的的动画
- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView;

// 在scrollView中  哪些控件是需要缩放的
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView;

// scrollView即将开始缩放
- (void)scrollViewWillBeginZooming:(UIScrollView *)scrollView withView:(UIView *)view NS_AVAILABLE_IOS(3_2);

//scrollView结束缩放
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale;

//scrollView 即将滚动到顶部
- (BOOL)scrollViewShouldScrollToTop:(UIScrollView *)scrollView;

//scrollView 已经滚动到顶部
- (void)scrollViewDidScrollToTop:(UIScrollView *)scrollView;