App_Delegate

App Delegate Lifecycle

Scene Delegate Migration

Swift 5 brought up with some new changes to app delegate and dividing them into 2 parts to cater it better for multiple screen sizes and iPadOS counterparts.
Good small snippet

State Lifecycle

Crash App

If for some reason you want to crash your application purposefully. You can just explicitly unwrap an optional which is guaranteed to be nil with a bang operator.

let optional: String? = nil
print(optional!)

I'm presuming we also have an option to send a SignalAlert / Interrupt to iOS Springboard to crash to home screen.

fatalError()
// OR
preconditionFailure()

SO | easiest-way-to-force-a-crash-in-swift

App lifecycle

applicationDidBecomeActive
applicationWillEnterForeground

didFinishLaunchingWithOptions

IOS Application Life Cycle

SO | applicationdidbecomeactive-getting-called-twice

Swift UI App State Reactive

struct ContentView: View {
    @Environment(\.scenePhase) var scenePhase

    var body: some View {
        Text("Hello, world!")
            .padding()
            .onChange(of: scenePhase) { newPhase in
                if newPhase == .active {
                    print("Active")
                } else if newPhase == .inactive {
                    print("Inactive")
                } else if newPhase == .background {
                    print("Background")
                }
            }
    }
}

hacking with swift | how-to-be-notified-when-your-swiftui-app-moves-to-the-background

Initial ViewController called Twice

Turns out when removing my Storyboard reference and replacing that logic in AppDelegate as well as Scene Delegate . I was invoking my ViewController from both places.
So with iOS 16 my current simulator. Scene Delegate Life cycle was calling my view controller first and then AppDelegate was also calling my View again.
Removing the AppDelegate UIWindow object initialization removed the viewDidLoad getting called twice.

Maybe relevant SO I didn't find a solution from the accepted one but still including it.
Link1
Link2

SwiftUI Migration

App Delegate migration

class FSAppDelegate: NSObject, UIApplicationDelegate {
  func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil
  ) -> Bool {
    // ...
    return true
  }
}

@main
struct FSApp: App {
  @UIApplicationDelegateAdaptor var delegate: FSAppDelegate 

  var body: some Scene {
    WindowGroup {
      ContentView()
    }
  }
}

app-delegate-scene-delegate-swiftui

Note

Open URL - Deep Links delegate won't work here. Just amazing in SwiftUI so you need to switch to onOpenURL { } linked here

func application(_ app: UIApplication,
                     open url: URL,
                     options: [UIApplication.OpenURLOptionsKey : Any] = [:]) -> Bool { }