iOS 常用控件的继承关系

开发时间久了，一些基础的东西会比较模糊，特别是理论方面会有所欠缺，今天就整理下一些常用控件的继承关系，也算是重新温习下基础吧

Objective-C 中所有的类都是继承自NSObject(别问为什么，我有点方)，我们常用的控件本质上其实也都是类，所以最终的顶层父类也就毫无疑问是NSObject

今天主要讲控件,iOS开发中的控件呢，说白了就是用户所能看到的所有东西基本上都可以称之为控件，UIButton，UILabel,UIScrollView......

控件是可以交互的，那么接受这些交互的类呢，就是UIResponder,简单的示例，UIView是可以触摸的吧(Touch)，比较常见的监听touch事件的方法

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event;//触摸屏幕
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event;//在屏幕上移动
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event;//离开屏幕
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event;//系统事件干扰

这些方法呢，其实不是UIView的方法，他是UIResponder的方法
所以单从控件的角度来说，UIResponder也是继承关系中处于相对顶端的位置

UIView：所有控件的父类或者说是间接父类，UIView它本身呢是继承自UIResponder，UIResponder他是继承自NSObject，所以目前的继承关系NSObject--> UIResponder--> UIView

下面一张图简单说下开发中经常用的控件继承关系

iOS控件继承关系.jpg

上图可以看到直接继承自UIView的为左侧部分，简介继承的为中间及右侧部分，子类拥有父类的方法以及属性
1.UIScrollView的子类一般都可以滑动

- (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

- (nullable UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView;     // return a view that will be scaled. if delegate returns nil, nothing happens
- (void)scrollViewWillBeginZooming:(UIScrollView *)scrollView withView:(nullable UIView *)view NS_AVAILABLE_IOS(3_2); // called before the scroll view begins zooming its content
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(nullable 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

/* Also see -[UIScrollView adjustedContentInsetDidChange]
 */
- (void)scrollViewDidChangeAdjustedContentInset:(UIScrollView *)scrollView API_AVAILABLE(ios(11.0), tvos(11.0));

2.UIControl的子类一般都可以添加监听点击的事件

// add target/action for particular event. you can call this multiple times and you can specify multiple target/actions for a particular event.
// passing in nil as the target goes up the responder chain. The action may optionally include the sender and the event in that order
// the action cannot be NULL. Note that the target is not retained.
- (void)addTarget:(nullable id)target action:(SEL)action forControlEvents:(UIControlEvents)controlEvents;

具体用到的控件可以查看其相关的API，注释都是比较好懂的，很基础的东西，希望可以帮到小白吧，毕竟我也是个小白 。。。。