相关链接
1. 创建storyboard
2. 向storyboard中拖拽UIViewController
3. 创建一个UIViewController,并关联到storyboard中
4. 可以使用代码获取UIViewController
let rootViewController = UIStoryboard(name: "SHS", bundle: nil).instantiateViewController(withIdentifier: "SHSLogViewControllerID") as UIViewController
window?.rootViewController = rootViewController