SwiftUI中的全局警报

我正试图在SwiftUI中呈现一个全局警报。无论当前在屏幕上显示/呈现的是什么，此警报都应显示在所有内容的顶部（例如，工作表）

这是我的代码：

@main
struct MyApp: App {
    
    @State private var showAlert = false
    
    var body: some Scene {
        WindowGroup {
            MainView()
                .onReceive(NotificationCenter.default.publisher(for:NSNotification.Name.SomeNotification), perform: { _ in
                    showAlert = true
                })
                .alert(
                    isPresented: $showAlert,
                    content: {Alert(title: Text("Alert!"))}
                )
        }
    }
}

在某些情况下，这将不起作用，例如，如果在屏幕上当前显示图纸时收到通知。在这种情况下，不会显示警报，控制台上会显示以下消息：

大宗报价 [演示文稿]尝试在已演示的（来自）上演示

这是有意义的，因为我试图在已经显示图纸的视图上显示警报

在UIKit上，我使用以下类实现了这一点：

class GlobalAlertController: UIAlertController {
    
    var globalPresentationWindow: UIWindow?
    
    func presentGlobally(animated: Bool, completion: (() -> Void)?) {
        globalPresentationWindow = UIWindow(frame: UIScreen.main.bounds)
        globalPresentationWindow?.rootViewController = UIViewController()
        globalPresentationWindow?.windowLevel = UIWindow.Level.alert + 1
        globalPresentationWindow?.backgroundColor = .clear
        globalPresentationWindow?.makeKeyAndVisible()
        globalPresentationWindow?.rootViewController?.present(self, animated: animated, completion: completion)
    }
    
    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        globalPresentationWindow?.isHidden = true
        globalPresentationWindow = nil
    }

}

此类允许我以以下方式在所有内容的顶部显示全局警报：

let alertController = GlobalAlertController(title: "Title", message: "Message", preferredStyle: .alert)
alertController.addAction(UIAlertAction(title: "Done", style: .cancel, handler: nil))
alertController.presentGlobally(animated: true, completion: nil)

---

有人知道如何在SwiftUI中实现类似的东西吗？

刚刚发现我实际上可以使用我的旧UIKit代码来实现这一点。唯一需要更改的是添加对场景的支持（SwiftUI按设计使用场景），如下所示：

class GlobalAlertController: UIAlertController {
    
    var globalPresentationWindow: UIWindow?
    
    func presentGlobally(animated: Bool, completion: (() -> Void)?) {
        globalPresentationWindow = UIWindow(frame: UIScreen.main.bounds)
        
        //This is needed when using scenes.
        if let currentWindowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene {
            globalPresentationWindow?.windowScene = currentWindowScene
        }

        globalPresentationWindow?.rootViewController = UIViewController()
        globalPresentationWindow?.windowLevel = UIWindow.Level.alert + 1
        globalPresentationWindow?.backgroundColor = .clear
        globalPresentationWindow?.makeKeyAndVisible()
        globalPresentationWindow?.rootViewController?.present(self, animated: animated, completion: completion)
    }
    
    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        globalPresentationWindow?.isHidden = true
        globalPresentationWindow = nil
    }

}

@main
struct MyApp: App {
    var body: some Scene {
        WindowGroup {
            MainView()
                .onReceive(NotificationCenter.default.publisher(for:NSNotification.Name.SomeNotification), perform: { _ in
                    let alertController = GlobalAlertController(title: "Title", message: "Message", preferredStyle: .alert)
                    alertController.addAction(UIAlertAction(title: "Done", style: .cancel, handler: nil))
                    alertController.presentGlobally(animated: true, completion: nil)
                })
        }
    }
}

现在我可以这样显示全局警报：

class GlobalAlertController: UIAlertController {
    
    var globalPresentationWindow: UIWindow?
    
    func presentGlobally(animated: Bool, completion: (() -> Void)?) {
        globalPresentationWindow = UIWindow(frame: UIScreen.main.bounds)
        
        //This is needed when using scenes.
        if let currentWindowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene {
            globalPresentationWindow?.windowScene = currentWindowScene
        }

        globalPresentationWindow?.rootViewController = UIViewController()
        globalPresentationWindow?.windowLevel = UIWindow.Level.alert + 1
        globalPresentationWindow?.backgroundColor = .clear
        globalPresentationWindow?.makeKeyAndVisible()
        globalPresentationWindow?.rootViewController?.present(self, animated: animated, completion: completion)
    }
    
    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        globalPresentationWindow?.isHidden = true
        globalPresentationWindow = nil
    }

}

@main
struct MyApp: App {
    var body: some Scene {
        WindowGroup {
            MainView()
                .onReceive(NotificationCenter.default.publisher(for:NSNotification.Name.SomeNotification), perform: { _ in
                    let alertController = GlobalAlertController(title: "Title", message: "Message", preferredStyle: .alert)
                    alertController.addAction(UIAlertAction(title: "Done", style: .cancel, handler: nil))
                    alertController.presentGlobally(animated: true, completion: nil)
                })
        }
    }
}

---

这是可行的，尽管更快捷的方法会更好。

以下内容解决了类似的问题，因此应该会有所帮助。