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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:

SceneDelegate.swift
ContentView.swift

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:

https://github.com/DKoenig82/simple_timer_swiftui

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