点按钮的时候，给alertView添加一个关联对象（被点击这个按钮），
objc_setAssociatedObject(alert, &kRepresentedObject,
sender,
OBJC_ASSOCIATION_RETAIN_NONATOMIC);
在UIAlertViewDelegate中取出关联对象（被点击的按钮）
UIButton *sender = objc_getAssociatedObject(alertView,
&kRepresentedObject);
&kRepresentedObject到底是什么东西，
kRepresentedObject从哪里来
static const char kRepresentedObject;
为什么会用char？？
主要代码如下 ，
#import "ViewController.h" #import <objc/runtime.h> @implementation ViewController static const char kRepresentedObject; #pragma mark - event response /** 按钮事件 */ - (IBAction)doSomething:(id)sender { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Alert" message:nil delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil]; objc_setAssociatedObject(alert, &kRepresentedObject, sender, OBJC_ASSOCIATION_RETAIN_NONATOMIC); [alert show]; } #pragma mark - UIAlertViewDelegate /** UIAlertViewDelegate */ - (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex { UIButton *sender = objc_getAssociatedObject(alertView, &kRepresentedObject); self.buttonLabel.text = [[sender titleLabel] text]; } @end
让我们再来看看其他关联对象是如何关联的
在分类中加入了几个属性
#import <Foundation/Foundation.h> #import "XTableViewCellItem.h" @interface NSArray (YDTableSectionView) @property (nonatomic, strong) XTableViewCellItem *sectionHeaderItem; @property (nonatomic, strong) XTableViewCellItem *sectionFooterItem; @end @interface YDtableSectionView : UIControl @property (nonatomic, strong) XTableViewCellItem *sectionItem; @end
m文件中这样实现
#import "NSArray+YDTableSectionView.h" #import <objc/runtime.h> @implementation NSArray (YDTableSectionView) - (void)setSectionHeaderItem:(XTableViewCellItem *)sectionHeaderItem { objc_setAssociatedObject(self, "sectionHeaderItem", sectionHeaderItem, OBJC_ASSOCIATION_RETAIN_NONATOMIC); } - (XTableViewCellItem *)sectionHeaderItem { return objc_getAssociatedObject(self, "sectionHeaderItem"); } - (void)setSectionFooterItem:(XTableViewCellItem *)sectionFooterItem { objc_setAssociatedObject(self, "sectionFooterItem", sectionFooterItem, OBJC_ASSOCIATION_RETAIN_NONATOMIC); } - (XTableViewCellItem *)sectionFooterItem { return objc_getAssociatedObject(self, "sectionFooterItem"); } @end
用的是
"sectionFooterItem"
而非
@"sectionFooterItem"
最上面用的是
static const char kRepresentedObject;
char kRepresentedObject;说是有是“”而非@“”
static 局部，本文件访问
const 常量，不变
ios 关联对象运用 objc_setAssociatedObject
原文：http://www.cnblogs.com/songxing10000/p/4932517.html