尝试呈现ViewController，其视图不在Windows层次结构中

问题

当前的viewController不是

rootViewController

UIApplication

解

只需在上找到topViewController

UIApplication Stack

let newViewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "viewController2")UIApplication.topViewController()?.present(newViewController, animated: true, completion: nil)

的扩展名可

UIApplication

extension UIApplication {    class func topViewController(base: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {        if let nav = base as? UINavigationController { return topViewController(base: nav.visibleViewController)        }        if let tab = base as? UITabBarController { if let selected = tab.selectedViewController {     return topViewController(base: selected) }        }        if let presented = base?.presentedViewController { return topViewController(base: presented)        }        return base    }}

参考：Gist