UIApplication.State demo

AppDelegate.swift

import UIKit

// case active = 0
// case inactive = 1
// case background = 2

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
  var window: UIWindow?
  
  override init() {
    super.init()
    print(#function, UIApplication.shared.applicationState.rawValue) // 2
  }
  
  func application(_ application: UIApplication, willFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
    print(#function, application.applicationState.rawValue) // 1
    return true
  }
  
  func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    print(#function, application.applicationState.rawValue) // 1
    window = UIWindow()
    window?.rootViewController = UIViewController()
    window?.rootViewController?.view.backgroundColor = .systemGreen
    window?.makeKeyAndVisible()
    return true
  }
  
  func applicationDidFinishLaunching(_ application: UIApplication) {} // is deprecated an never called
  
  func applicationWillResignActive(_ application: UIApplication) {
    print(#function, application.applicationState.rawValue, terminator: " ") // 0
    DispatchQueue.main.async {
      print(application.applicationState.rawValue) // 1
    }
  }
  
  func applicationDidEnterBackground(_ application: UIApplication) {
    print(#function, application.applicationState.rawValue) // 2
  }
  
  func applicationWillEnterForeground(_ application: UIApplication) {
    print(#function, application.applicationState.rawValue, terminator: " ") // 2
    DispatchQueue.main.async {
      print(application.applicationState.rawValue) // 1
    }
  }
  
  func applicationDidBecomeActive(_ application: UIApplication) {
    print(#function, application.applicationState.rawValue) // 0
  }
  
  func applicationWillTerminate(_ application: UIApplication) {
    print(#function, application.applicationState.rawValue) // 2
  }
}