View with NSWindowDelegate, listens window events

TimerTest.swift

import SwiftUI
    
struct TimerTest: View {
    @State var date = Date()
    @State var showSubView = false
    var windowDelegate: MyWindowDelegate = MyWindowDelegate()
    
    var body: some View {
        ZStack{
            if showSubView {
                VStack {
                    Text(" Timer Stoped?")
                    Button("Back") {
                        self.showSubView = false
                    }
                }
            }
            else {
                VStack {
                    Button("Switch to subview"){
                        self.showSubView = true
                    }

                    Text("date: \(date)")
                        .onAppear(perform: {
                            self.windowDelegate.timer = Timer.scheduledTimer(withTimeInterval: 1,
                                            repeats: true,
                                            block: {_ in
                                              self.date = Date()
                                              NSLog("🔷 onAppear timer triggered")
                                             })
                        })
                        .onDisappear(perform: {
                            self.windowDelegate.timer?.invalidate()
                            self.windowDelegate.timer = nil
                            NSLog("🔶 onDisappear stop timer")
                        })
                }
            }
        }
        .frame(width: 500, height: 300)
    }
    
    class MyWindowDelegate: NSObject, NSWindowDelegate {
        var timer: Timer?
        
        func windowWillClose(_ notification: Notification) {
            NSLog("🐶 window will close. Stop timer")
            self.timer?.invalidate()
            self.timer = nil
        }
    }
}