NSSet *connectedScenes = [UIApplication sharedApplication].connectedScenes;
for (UIScene *scene in connectedScenes) {
    if (scene.activationState == UISceneActivationStateForegroundActive && [scene isKindOfClass:[UIWindowScene class]]) {
        UIWindowScene *windowScene = (UIWindowScene *)scene;
        for (UIWindow *window in windowScene.windows) {
            UIViewController *viewController = window.rootViewController;
            // Get the instance of your view controller
            if ([viewController isKindOfClass:[YOUR_VIEW_CONTROLLER class]]) {
                // Your code here...
                break;
            }
        }
    }
}

对于Objective-C解决方案也是如此

@implementation UIWindow (iOS13)

+ (UIWindow*) keyWindow {
   NSPredicate *isKeyWindow = [NSPredicate predicateWithFormat:@"isKeyWindow == YES"];
   return [[[UIApplication sharedApplication] windows] filteredArrayUsingPredicate:isKeyWindow].firstObject;
}

@end

这是我的解决方案:

let keyWindow = UIApplication.shared.connectedScenes
        .filter({$0.activationState == .foregroundActive})
        .compactMap({$0 as? UIWindowScene})
        .first?.windows
        .filter({$0.isKeyWindow}).first

使用如:

keyWindow?.endEditing(true)

您可能知道，由于可能存在多个场景，因此不建议使用键窗口。最方便的解决方案是提供一个currentWindow作为扩展，然后进行搜索和替换。

extension UIApplication {
    var currentWindow: UIWindow? {
        connectedScenes
            .compactMap { $0 as? UIWindowScene }
            .flatMap { $0.windows }
            .first { $0.isKeyWindow }
    }
}

(在运行于Xcode 13.2.1的iOS 15.2上测试)

extension UIApplication {
    
    var keyWindow: UIWindow? {
        // Get connected scenes
        return UIApplication.shared.connectedScenes
            // Keep only active scenes, onscreen and visible to the user
            .filter { $0.activationState == .foregroundActive }
            // Keep only the first `UIWindowScene`
            .first(where: { $0 is UIWindowScene })
            // Get its associated windows
            .flatMap({ $0 as? UIWindowScene })?.windows
            // Finally, keep only the key window
            .first(where: \.isKeyWindow)
    }
    
}

如果你想在关键的UIWindow中找到呈现的UIViewController，这是另一个你可以发现有用的扩展:

extension UIApplication {
    
    var keyWindowPresentedController: UIViewController? {
        var viewController = self.keyWindow?.rootViewController
        
        // If root `UIViewController` is a `UITabBarController`
        if let presentedController = viewController as? UITabBarController {
            // Move to selected `UIViewController`
            viewController = presentedController.selectedViewController
        }
        
        // Go deeper to find the last presented `UIViewController`
        while let presentedController = viewController?.presentedViewController {
            // If root `UIViewController` is a `UITabBarController`
            if let presentedController = presentedController as? UITabBarController {
                // Move to selected `UIViewController`
                viewController = presentedController.selectedViewController
            } else {
                // Otherwise, go deeper
                viewController = presentedController
            }
        }
        
        return viewController
    }
    
}

你可以把它放在任何你想要的地方，但我个人把它作为UIViewController的扩展。

这让我可以添加更多有用的扩展，比如更容易地呈现UIViewControllers:

extension UIViewController {
    
    func presentInKeyWindow(animated: Bool = true, completion: (() -> Void)? = nil) {
        DispatchQueue.main.async {
            UIApplication.shared.keyWindow?.rootViewController?
                .present(self, animated: animated, completion: completion)
        }
    }
    
    func presentInKeyWindowPresentedController(animated: Bool = true, completion: (() -> Void)? = nil) {
        DispatchQueue.main.async {
            UIApplication.shared.keyWindowPresentedController?
                .present(self, animated: animated, completion: completion)
        }
    }
    
}

支持iOS 13及以上版本。

为了继续使用与旧iOS版本相似的语法，UIApplication.shared.keyWindow创建以下扩展:

extension UIApplication {
    var mainKeyWindow: UIWindow? {
        get {
            if #available(iOS 13, *) {
                return connectedScenes
                    .flatMap { ($0 as? UIWindowScene)?.windows ?? [] }
                    .first { $0.isKeyWindow }
            } else {
                return keyWindow
            }
        }
    }
}

使用

if let keyWindow = UIApplication.shared.mainKeyWindow {
    // Do Stuff
}