Swift 基本语法03-"if let"和"guard let"

1.

        /// 如果JY_WINDOW有rootViewController， 并且rootViewController类型是AdvertisementViewController，就执行stopPlay()
        if let vc = JY_WINDOW?.rootViewController as? AdvertisementViewController {
            vc.stopPlay()
        }

　　

2.详情
https://www.jianshu.com/p/e1fe08c5db1a