在选择特定视图时，如何使用生命周期方法？

Question

我目前正在使用SwiftUI开发一个应用程序。

这个应用程序有两个视图控制一个Tab视图。

只有在选择特定视图时，我才希望在sceneDidBecomeActive和sceneWillEnterForeground中使用这些方法。

无论选择哪个视图，这些方法都可以工作。

我怎样才能完成这个请求？

SceneDelegate.swift

import SwiftUI

class SceneDelegate: UIResponder, UIWindowSceneDelegate {
    
    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
       
        let contentView = ContentView()

        if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
            window.rootViewController = UIHostingController(rootView: contentView)
            self.window = window
            window.makeKeyAndVisible()
        }
    }
    func sceneDidDisconnect(_ scene: UIScene) {
    }
    func sceneDidBecomeActive(_ scene: UIScene) {
        // I want use this print method only when FirstView is selected
        print("selected FirstVIew")
    }
    func sceneWillResignActive(_ scene: UIScene) {
    }
    func sceneWillEnterForeground(_ scene: UIScene) {
        // I want use this print method only when FirstView is selected
        print("selected FirstVIew")
    }
    func sceneDidEnterBackground(_ scene: UIScene) {
    }
}

ContentView.swift

import SwiftUI

struct ContentView: View {
    
   var body: some View {
        TabView {
           FirstView()
                .tabItem {
                        Text("First")
            }.tag(1)
           SecondView()
                .tabItem {
                        Text("Second")
            }.tag(2)
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

FirstView.swift

import SwiftUI

struct FirstView: View {
    var body: some View {
        Text("FirstView")
    }
}

struct FirstView_Previews: PreviewProvider {
    static var previews: some View {
        FirstView()
    }
}

SecondView.swift

import SwiftUI

struct SecondView: View {
    var body: some View {
        Text("SecondView")
    }
}

struct SecondView_Previews: PreviewProvider {
    static var previews: some View {
        SecondView()
    }
}

Xcode: 11.7版

Swift: Swift 5

Answer 1

SceneDelegate方法处理的是应用程序的生命周期，而不是视图的生命周期。因此，当选择视图时，您不能“运行”它们。

不过，您可以做的是使用UserDefaults。

// When first view selected
UserDefaults.standard.set("First View", forKey: "selectedView")

// In SceneDelegate
func sceneDidBecomeActive(_ scene: UIScene) {
    if let selected = UserDefaults.standard.string(forKey: "selectedView"),    
             selected == "First View" {
        print("selected FirstVIew")
    }
}

func sceneWillEnterForeground(_ scene: UIScene) {
    if let selected = UserDefaults.standard.string(forKey: "selectedView"),          
              selected == "First View" {
        print("selected FirstVIew")
    }
}