IOS控件UIScrollView详解（基本方法、属性和delegate用法）

1，UIScrollView 常用属性和使用方法

--官方查阅文档  https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIScrollView_Class/Reference/UIScrollView.html 
--介绍：UIScrollView用于在一个小范围里显示很大的内容的控件。通过用户平滑、手捏手势，在这个小区域里查看不同内容。是UITableView和UITextView的父类。它是视图，但是比较特殊，可以看成把它看成2层的结构。上面是它的frame层，跟一般试图一样，是它的可见区域，下面层是contentView，可以滑动。 
============常用属性============
--CGPoint contentOffSet：contentView的偏移值(正常contentOffSet.x/y值都为正数，但有时（bounces = YES）拽出边界了或者contentInset设置了，还是会出现负数，伴随着contentView滑动，总在改变);
--CGSize contentSize：contentView的大小；
--UIEdgeInsets contentInset：contentView四周的扩展大小，相当改变ContentView的大小，但不是改变contentSize(UIEdgeInsets是个结构体，里面的数值可能是负数，所以扩展的结果可能是contentView被蚕食了一部分。但不管contentView变大了还是变小了，contentOffSet的值还是相比原来大小的偏移);
--id<UIScrollerViewDelegate> delegate：它的代理;
--BOOL directionalLockEnabled：默认是NO，可以在垂直和水平方向同时运动。当值是YES时，假如一开始是垂直或者是水平运动，那么接下来会锁定另外一个方向的滚动。假如一开始是对角方向滚动，则不会禁止某个方向(测试锁定不了，难道是contentsize跟frame高度或宽度一样时用的)
--BOOL bounces：默认是 yes，就是滚动超过边界会反弹有反弹回来的效果。假如是 NO，那么滚动到达边界会立刻停止
--UIScrollViewIndicatorStyle  indicatorStyle：设定滚动条的样式；
--BOOL alwaysBounceVertical：默认no，控制垂直方向遇到边框是否反弹(但bounces为NO时，它为yes，也不反弹。/if YES and bounces is YES, even if content is smaller than bounds, allow drag vertically，测试不好使)；
--BOOL alwaysBounceHorizontal：默认no，控制水平方向遇到边框是否反弹(但bounces为NO时，它为yes，也不反弹);
--BOOL pagingEnabled：default NO，contentView是否整页翻动；
--BOOL scrollEnabled：default YES，contentView是否能滚动；
--BOOL showsHorizontalScrollIndicator：default YES，是否显示水平方向的滚动条；
--BOOL showsVerticalScrollIndicator：default YES  是否显示垂直方向的滚动条；
--UIEdgeInsets scrollIndicatorInsets：滚动条在scrollerView中的位置的扩展；
--float  decelerationRate：手指放开后的减速率（测试发现设定这个值没用);

2，UIScrollView 常用的方法和使用方式

3，UIScrollView代理方法详解

- (void)scrollViewDidScroll:(UIScrollView *)scrollView;                                               // any offset changes
- (void)scrollViewDidZoom:(UIScrollView *)scrollView NS_AVAILABLE_IOS(3_2); // any zoom scale changes

// called on start of dragging (may require some time and or distance to move)
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView;
// called on finger up if the user dragged. velocity is in points/millisecond. targetContentOffset may be changed to adjust where the scroll view comes to rest
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset NS_AVAILABLE_IOS(5_0);
// called on finger up if the user dragged. decelerate is true if it will continue moving afterwards
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate;

- (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView;   // called on finger up as we are moving
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView;      // called when scroll view grinds to a halt

- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView; // called when setContentOffset/scrollRectVisible:animated: finishes. not called if not animating

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView;     // return a view that will be scaled. if delegate returns nil, nothing happens
- (void)scrollViewWillBeginZooming:(UIScrollView *)scrollView withView:(UIView *)view NS_AVAILABLE_IOS(3_2); // called before the scroll view begins zooming its content
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale; // scale between minimum and maximum. called after any 'bounce' animations

- (BOOL)scrollViewShouldScrollToTop:(UIScrollView *)scrollView;   // return a yes if you want to scroll to the top. if not defined, assumes YES
- (void)scrollViewDidScrollToTop:(UIScrollView *)scrollView;      // called when scrolling animation finished. may be called immediately if already at top