SwiftUI: respond to app termination on macOS

问题

I am creating a cross-platform app with SwiftUI 2.0. The app's lifecycle is managed by SwiftUI, so there is no app or scene delegate. If possible, I would like to keep it that way. In order to persist data when the app quits or enters the background, I am watching for changes on scenePhase.

@main
struct MyApp: App {
    
    @Environment(\.scenePhase) var scenePhase
    @StateObject var dataModel = DataModel()
    
    var body: some Scene {
        WindowGroup {
            ContentView()
                .onChange(of: scenePhase) { newScenePhase in
                    switch newScenePhase {
                    case .background, .inactive:
                        dataModel.save()
                    default: break
                }
        }
    }
}

However, this approach has an inherent flaw: on macOS, when the app is terminated, there is no change in scenePhase, and thus the data is not persisted. Is there a separate mechanism for detecting app termination? Does SwiftUI have the equivalent of applicationWillTerminate:?

回答1:

You can inject application delegate via adapter. Use as the following example:

#if os(macOS)
class AppDelegate: NSObject, NSApplicationDelegate {

    func applicationWillTerminate(_ aNotification: Notification) {
        // Insert code here to tear down your application
    }
}
#endif

@main
struct MyApp: App {

#if os(macOS)
    @NSApplicationDelegateAdaptor(AppDelegate.self) var appDelegate
#endif

    // ... other code
}

来源：https://stackoverflow.com/questions/64940411/swiftui-respond-to-app-termination-on-macos