David Koenig's Blog

Simple Timer - SwiftUI


In this case study app, I made a simple Timer. The Timer starts, when opening and running the App. It is easier to make a Timer in SwiftUI, than before.

In the Xcode Project we have to update 2 Files which should look like this:

In the SceneDelegate.swift File, we have to initialize the Timer to the Content View.

import UIKit import SwiftUI class SceneDelegate: UIResponder, UIWindowSceneDelegate { var window: UIWindow? func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) { // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`. // If using a storyboard, the `window` property will automatically be initialized and attached to the scene. // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead). // Use a UIHostingController as window root view controller if let windowScene = scene as? UIWindowScene { let window = UIWindow(windowScene: windowScene) window.rootViewController = UIHostingController(rootView: ContentView(referenceDate: Date(timeIntervalSinceNow: 86400))) self.window = window window.makeKeyAndVisible() } } func sceneDidDisconnect(_ scene: UIScene) { // Called as the scene is being released by the system. // This occurs shortly after the scene enters the background, or when its session is discarded. // Release any resources associated with this scene that can be re-created the next time the scene connects. // The scene may re-connect later, as its session was not neccessarily discarded (see `application:didDiscardSceneSessions` instead). } func sceneDidBecomeActive(_ scene: UIScene) { // Called when the scene has moved from an inactive state to an active state. // Use this method to restart any tasks that were paused (or not yet started) when the scene was inactive. } func sceneWillResignActive(_ scene: UIScene) { // Called when the scene will move from an active state to an inactive state. // This may occur due to temporary interruptions (ex. an incoming phone call). } func sceneWillEnterForeground(_ scene: UIScene) { // Called as the scene transitions from the background to the foreground. // Use this method to undo the changes made on entering the background. } func sceneDidEnterBackground(_ scene: UIScene) { // Called as the scene transitions from the foreground to the background. // Use this method to save data, release shared resources, and store enough scene-specific state information // to restore the scene back to its current state. } }

In the ContentView.swift File we implement the UI and the actual Timer with the a counter String.

import SwiftUI struct ContentView : View { @State var nowDate: Date = Date() let referenceDate: Date var timer: Timer { Timer.scheduledTimer(withTimeInterval: 1, repeats: true) {_ in self.nowDate = Date() } } var body: some View { NavigationView { ZStack { RoundedRectangle(cornerRadius: 50, style: .continuous).fill(Color.red).padding() Text("24 hours from Now:").foregroundColor(.white) .font(.largeTitle) .offset(x:0, y: -40) Text(countString(from: referenceDate)).foregroundColor(.white) .font(.title) .offset(x:0, y: 40) .onAppear(perform: { _ = self.timer }) } .navigationBarTitle(Text("Timer")) } } func countString(from date: Date) -> String { let calendar = Calendar(identifier: .gregorian) let components = calendar .dateComponents([.day, .hour, .minute, .second], from: nowDate, to: referenceDate) return String(format: "%0dd:%0dh:%0dm:%0ds", components.day ?? 00, components.hour ?? 00, components.minute ?? 00, components.second ?? 00) } } #if DEBUG struct ContentView_Previews : PreviewProvider { static var previews: some View { ContentView(referenceDate: Date(timeIntervalSinceNow: 86400)) } } #endif

You can download the project at Github:

David Koenig