我们都会声明一个弱引用在block中使用, 目的就是防止循环引用, 那么weakSelf与strongSelf一起使用目的是什么呢? 首先先定义2个宏:
#define YXWeakSelf(type) __weak typeof(type) weak##type = type; #define StrongSelf(type) __strong typeof(type) type = weak##type;
在Controller中YXWeakSelf(self)与YXStrongSelf(self)一起使用情况很多，为了防止循环引用，还是不懂原因的见如下实例：
我们创建一个shop并且在shop.myBlock代码块中使用弱引用YXWeakSelf(shop)
LRShop *shop = [[LRShop alloc]init]; shop.string = @"welcome to our company"; //弱引用 YXWeakSelf(shop) shop.myBlock = ^{ NSLog(@"%@",weakshop.string); }; shop.myBlock();
YXWeakSelf(shop)与YXStrongSelf(shop)一起使用
LRShop *shop = [[LRShop alloc]init]; shop.string = @"welcome to our company"; //弱引用 YXWeakSelf(shop); shop.myBlock = ^{ //强引用 YXStrongSelf(shop) NSLog(@"%@",shop.string); }; shop.myBlock();
这2个打印结果都是shop.string有值并且shop也销毁了, 看起来是没什么区别:
仅仅使用YXWeakSelf(shop)并且在myBlock中增加一个延迟3秒在输出就会出现问题, 虽然对象销毁了, 输出的值却是null
//弱引用 YXWeakSelf(shop); shop.myBlock = ^{ dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ NSLog(@"%@",weakshop.string); }); }; shop.myBlock();
如果YXWeakSelf(shop)与YXStrongSelf(shop)一起使用输出的shop.string有值,对象也销毁了, 我就不再截图给大家看了!
//弱引用 YXWeakSelf(shop) shop.myBlock = ^{ //强引用 YXStrongSelf(shop) dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ NSLog(@"%@",shop.string); }); }; shop.myBlock();
通过上面一堆的解释, 我们明显发现YXWeakSelf(shop)与YXStrongSelf(shop)一起使用的好处, 不但能打印出我想要的值,而且也不会造成循环引用 , 在开发中这两个方法可以根据实际情况进行使用!
