objc_setAssociatedObject 使用

- (void)viewDidLoad {
    [super viewDidLoad];
   
     
//    static const char associatedButtonkey;
     
     
     
    UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];
    [btn setTitle:@"点我" forState:UIControlStateNormal];
    [self.view addSubview:btn];
    [btn setFrame:CGRectMake(50, 50, 50, 50)];
    btn.backgroundColor = [UIColor redColor];
     
    [btn addTarget:self action:@selector(click:) forControlEvents:UIControlEventTouchUpInside];
     
    // Do any additional setup after loading the view, typically from a nib.
     
}
-(void)click:(UIButton *)sender
{
    NSString *message = @"你是谁";
     
    UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"提示" message:@"我要传值·" delegate:self cancelButtonTitle:@"确定" otherButtonTitles:nil];
    alert.delegate = self;
    [alert show];
     
    //#import <objc/runtime.h>头文件
    //objc_setAssociatedObject需要四个参数：源对象，关键字，关联的对象和一个关联策略。
     
    //1 源对象alert
    //2 关键字 唯一静态变量key associatedkey
    //3 关联的对象 sender
    //4 关键策略  OBJC_ASSOCIATION_ASSIGN
//    enum {
//        OBJC_ASSOCIATION_ASSIGN = 0,           若引用/**< Specifies a weak reference to the associated object. */
//        OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1, /**< Specifies a strong reference to the associated object.
//                                                *   The association is not made atomically. */
//        OBJC_ASSOCIATION_COPY_NONATOMIC = 3,   /**< Specifies that the associated object is copied.
//                                                *   The association is not made atomically. */
//        OBJC_ASSOCIATION_RETAIN = 01401,       /**< Specifies a strong reference to the associated object.
//                                                *   The association is made atomically. */
//        OBJC_ASSOCIATION_COPY = 01403          /**< Specifies that the associated object is copied.
//                                                *   The association is made atomically. */
//    };
     
     
    objc_setAssociatedObject(alert, @"msgstr", message,OBJC_ASSOCIATION_ASSIGN);
    //把alert和message字符串关联起来，作为alertview的一部分，关键词就是msgstr，之后可以使用objc_getAssociatedObject从alertview中获取到所关联的对象，便可以访问message或者btn了
     
//    即实现了关联传值
    objc_setAssociatedObject(alert, @"btn property",sender,OBJC_ASSOCIATION_ASSIGN);
}
-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
     
     
    //通过 objc_getAssociatedObject获取关联对象
    NSString  *messageString =objc_getAssociatedObject(alertView, @"msgstr");
     
     
    UIButton *sender = objc_getAssociatedObject(alertView, @"btn property");
    NSLog(@"%ld",buttonIndex);
    NSLog(@"%@",messageString);
    NSLog(@"%@",[[sender titleLabel] text]);
     
     
    //使用函数objc_removeAssociatedObjects可以断开所有关联。通常情况下不建议使用这个函数，因为他会断开所有关联。只有在需要把对象恢复到“原始状态”的时候才会使用这个函数。
}
 
终端打印：
2015-07-22 16:18:35.294 test[5174:144121] 0
2015-07-22 16:18:35.295 test[5174:144121] 你是谁
2015-07-22 16:18:35.295 test[5174:144121] 点我

　　tableviewcell上的按钮等元素需要传值时，只有一个tag而且是nsinteger，是不是很郁闷？用这个就OK啦^_^