提要：

UIControl 是基於Target-Action模式的控件的基類

不應該直接使用

繼承自UIView

內容：

UIControl可以實現自定義控件，支持 subclass

Apple Doc給extend UIControl的建議：

1.針對於特定實踐，觀察or修改（實現想怎麼調用就怎麼調用），action消息的分發。

2.提供自定義跟蹤行為（想讓控件有什麼樣的track行為）

You may want to extend a UIControl subclass for either of two reasons:

• To observe or modify the dispatch of action messages to targets for particular events

  To do this, override sendAction:to:forEvent:, evaluate the passed-in selector, target object, or UIControlEvents bit mask, and proceed as required.

• To provide custom tracking behavior (for example, to change the highlight appearance)

  To do this, override one or all of the following methods: beginTrackingWithTouch:withEvent:, continueTrackingWithTouch:withEvent:, endTrackingWithTouch:withEvent:.

  代碼舉例

  實現控件點擊3才有消息分發即（方法調用）

   

  - (void)sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event {

  if (touchTime == 3) {

  touchTime = 0;

  if ([target respondsToSelector:action]) {

  #pragma clang diagnostic push

  #pragma clang diagnostic ignored "-Warc-performSelector-leaks"

  [target performSelector:action];

  #pragma clang diagnostic pop

  }

  }

  }

  - (BOOL)beginTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {

  NSLog(@"%s", __FUNCTION__);

  BOOL isBegin = NO;

  if (++touchTime < 3) {

  isBegin = NO;

  } else {

  isBegin = YES;

  }

  return isBegin;

  }

  - (void)endTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {

  NSLog(@"%s", __FUNCTION__);

  }