OC底层运行时关联理解

UIAlertView的扩展

.h文件

import

typedef void (^successBlock)(NSInteger buttonIndex);
@interface UIAlertView (Block)

• (void)showWithBlock:(successBlock)block;@end

.m文件

import "UIAlertView+Block.h"

import

static const char alertKey;
@implementation UIAlertView (Block)

• (void)showWithBlock:(successBlock)block{
  if (block) {
  objc_setAssociatedObject(self, &alertKey, block,OBJC_ASSOCIATION_RETAIN_NONATOMIC);
  self.delegate = self;
  }
  [self show];
  }
• (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
  successBlock block = objc_getAssociatedObject(self, &alertKey); block(buttonIndex);
  }
  @end

UIButton的扩展

.h文件

import

typedef void (^btnBlock)();
@interface UIButton (Block)

• (void)handelWithBlock:(btnBlock)block;
  @end

.m文件

import "UIButton+Block.h"

import

static const char btnKey;
@implementation UIButton (Block)

• (void)handelWithBlock:(btnBlock)block{
  if (block) {
  objc_setAssociatedObject(self, &btnKey, block, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
  }
  [self addTarget:self action:@selector(btnAction) forControlEvents:UIControlEventTouchUpInside];
  }
• (void)btnAction{
  btnBlock block = objc_getAssociatedObject(self, &btnKey);
  block();
  }
  @end

tips: 使用objc_setAssociatedObject，需要引入头文件#import

void objc_setAssociatedObject(id object, const void key, id value, objc_AssociationPolicy policy);
id objc_getAssociatedObject(id object, const void key);

这两个方法可以让一个对象和另一个对象关联，就是说一个对象可以保持对另一个对象的引用，并获取那个对象。有了这些，就能实现属性功能了。 policy可以设置为以下这些值：
enum {
OBJC_ASSOCIATION_ASSIGN = 0,
OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1,
OBJC_ASSOCIATION_COPY_NONATOMIC = 3,
OBJC_ASSOCIATION_RETAIN = 01
OBJC_ASSOCIATION_COPY = 01403};