ios runtime 动态属性objc_setAssociatedObject和objc_getAssociatedObject

////  ViewController.m//  objc_runtime////  Created by 王飞 on 16/4/11.//  Copyright © 2016年 com.startchina. All rights reserved.//#import "ViewController.h"#import <objc/runtime.h>@interface ViewController ()@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    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。}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end