runtime动态添加属性

<span style="font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.5px; background-color: rgb(254, 254, 242);">使用运行时库，必须要先引入 objc/runtime.h</span>

<span style="font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.5px; background-color: rgb(254, 254, 242);">看一个类别和动态添加属性的例子
UILabel+Associate.h
#import <UIKit/UIKit.h>
@interface UILabel (Associate)

- (void) setFlashColor:(UIColor *) flashColor;

- (UIColor *) getFlashColor;

</span>

<span style="font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.5px; background-color: rgb(254, 254, 242);">@end</span><span style="font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.5px; background-color: rgb(254, 254, 242);">UILabel+Associate.m</span>

<span style="font-family: Arial, Helvetica, sans-serif;">#import "UILabel+Associate.h"</span>

#import <objc/runtime.h>

@implementation UILabel (Associate)

static char flashColorKey;

- (void) setFlashColor:(UIColor *) flashColor{
    objc_setAssociatedObject(self, &flashColorKey, flashColor, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (UIColor *) getFlashColor{
   return objc_getAssociatedObject(self, &flashColorKey);
}

@end

调用代码：

UILabel *lab = [[UILabel alloc] init];
    [lab setFlashColor:[UIColor redColor]];
    NSLog(@"%@", [lab getFlashColor]);