在Block中一起使用weakSelf与strongSelf的含义

1.在Block中一起使用weakSelf与strongSelf的含义

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 LRWeakSelf(type)  __weak typeof(type) weak##type = type;

#define LRStrongSelf(type)  __strong typeof(type) type = weak##type;

我们创建一个shop并且在shop.myBlock代码块中使用弱引用LRWeakSelf(shop);

LRShop *shop = [[LRShop alloc]init];
shop.string = @"welcome to our company";
//弱引用
LRWeakSelf(shop);
shop.myBlock = ^{
NSLog(@"%@",weakshop.string);
};
shop.myBlock();

LRWeakSelf(shop);与LRStrongSelf(shop);一起使用

LRShop *shop = [[LRShop alloc]init];
shop.string = @"welcome to our company";
//弱引用
LRWeakSelf(shop);
shop.myBlock = ^{
//强引用
LRStrongSelf(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:

图1

仅仅使用LRWeakSelf(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
LRWeakSelf(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();

图2

如果LRWeakSelf(shop);与LRStrongSelf(shop);一起使用输出的shop.string有值,对象也销毁了

//弱引用
LRWeakSelf(shop);
shop.myBlock = ^{
//强引用
LRStrongSelf(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LRWeakSelf(shop);与LRStrongSelf(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!