Runtime 实现 动态添加属性

利用动态加载为对象添加一个 block 点击属性;

.h 文件

 #import <UIKit/UIKit.h>

 @interface UIView (Tap)
 /**
  *  动态添加手势
  */
 - (void)setTapActionWithBlock:(void (^)(void))block ;
 @end

.m 文件

 #import "UIView+Tap.h"
 #import <objc/runtime.h>
 /**
  *  动态添加手势
  */
 static const char *ActionHandlerTapGestureKey;

 @implementation UIView (Tap)

 - (void)setTapActionWithBlock:(void (^)(void))block {

     self.userInteractionEnabled = YES;

     UITapGestureRecognizer *gesture = objc_getAssociatedObject(self, &ActionHandlerTapGestureKey);

     if (!gesture) {
         gesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleActionForTapGesture:)];
         [self addGestureRecognizer:gesture];
         objc_setAssociatedObject(self, &ActionHandlerTapGestureKey, gesture, OBJC_ASSOCIATION_RETAIN);
     }

     objc_setAssociatedObject(self, &ActionHandlerTapGestureKey, block, OBJC_ASSOCIATION_COPY);
 }

 - (void)handleActionForTapGesture:(UITapGestureRecognizer *)gesture {
     if (gesture.state == UIGestureRecognizerStateRecognized)  {
         void(^action)(void) = objc_getAssociatedObject(self, &ActionHandlerTapGestureKey);
         if (action)  {
             action();
         }
     }
 }
 @end