在Block中使用weakSelf与strongSelf的意义

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!