SwiftUI 中的全局警报

Question

我正在尝试在 SwiftUI 中呈现全局警报。此警报应显示在所有内容之上，无论当前在屏幕上显示/呈现什么内容（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!"))}
                )
        }
    }
}

这在某些情况下不起作用，例如，如果在屏幕上当前呈现工作表时收到通知。在这种情况下，不会显示警报，并且控制台上会显示以下消息：

块引用 [演示] 尝试在 < TtGC7SwiftUI19UIHostingControllerGVS_15ModifiedContentVS_7AnyViewVS_12RootModifier _: 0x7fbee642ac60> 上呈现 <SwiftUI.PlatformAlertController: 0x7fbee6921400> （来自 < TtGC7SwiftUI19UIHostingControllerGVS_15ModifiedContentVS_7AnyViewVS_ 12RootModifier _: 0x7fbee642ac60>) 已经呈现 < TtGC7SwiftUI22SheetHostingControllerVS_7AnyView : 0x7fbee8405360>。

这是有道理的，因为我试图在已经呈现工作表的视图上呈现警报。

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
    }

}

这个类允许我以这种方式在所有内容之上显示全局警报：

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？

Answer 1

刚刚发现我实际上可以使用旧的 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
    }

}

现在我可以像这样显示全局警报：

@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)
                })
        }
    }
}

它确实有效，尽管更类似于 SwiftUI 的方法会更好。