ios扩展机制objc_setAssociatedObject，objc_getAssociatedObject

这个可以解决变量传递问题, 就不用定义全局的了.

使用例子：

首先导入头文件：#import <objc/runtime.h>

设置静态常量：static char alertinfokey;

- (IBAction)showAlertAction:(id)sender {

UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"title" message:@"warn" delegate:selfcancelButtonTitle:@"cancel" otherButtonTitles:@"ok", nil];

objc_setAssociatedObject(alert, &alertinfokey, @"test value", OBJC_ASSOCIATION_RETAIN);

[alert show];

[alert release];

}

-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex{

if (buttonIndex == 0) {

NSLog(@"== : %@",objc_getAssociatedObject(alertView, &alertinfokey));

}

}

输出结果：== : test value