- (NSString *)urlString {
return objc_getAssociatedObject(self, "str");
}
- (void)setUrlString:(NSString *)urlString {
//可以在运行期间给某个对象增加属性
//关联对象
objc_setAssociatedObject(self, "str", urlString, OBJC_ASSOCIATION_COPY_NONATOMIC);
}