如何使用没有任何页面转换或任何重启应用程序的方法 [英] How can I use a method without any page transition or any reboot app

问题描述

我目前正在使用 SwiftUI 开发应用程序.

我想在视图出现时使用一个方法.

对于我在下面附加的代码，我可以在应用启动时使用 print 方法并在页面之间进行一些转换.

---

但是当我重新打开应用程序时，我想使用 print 方法，如下所示:

• 1:在模拟器上运行代码(我可以看到 print 方法有效).

• 2:按下主页按钮.

• 3:点击应用程序图标打开应用程序(我看不到 print 方法有效).

  (*) 我想在这里使用 print 方法.

在这种情况下，我怎样才能按照自己的意愿去做?

---

代码如下:

导入 SwiftUI结构内容视图:查看{@State 私有变量选择 = 0var主体:一些视图{TabView(selection: $selection){文本(第一次查看").onAppear(){打印(第一")}.tabItem {文本(第一")}.tag(0)文本(第二视图").tabItem {文本(第二")}.tag(1)}}}struct ContentView_Previews: PreviewProvider {静态 var 预览:一些视图 {内容视图()}}

---

添加:

我在 SceneDelegate.swift<中使用 sceneWillEnterForeground 或 sceneWillResignActive/p>

但在这种情况下，当应用程序成为前台时，SecondView 也能正常工作.而且我想修改代码以仅当应用程序成为具有 FirstView 的前台时才能使用该功能.

有没有办法做到这一点?

SceneDelegate.swift

func sceneDidBecomeActive(_scene: UIScene) {打印(变得活跃")}funcsceneWillEnterForeground(_场景:UIScene){打印(前景")}

---

Xcode:11.7 版

斯威夫特:斯威夫特 5

解决方案

您可以使用 @EnvironmentObject 来跟踪应用程序状态(通过观察通知):

class AppState: ObservableObject {@Published var isActive = true私有变量观察者 = [NSObjectProtocol]()在里面() {观察者.追加(NotificationCenter.default.addObserver(forName: UIApplication.didBecomeActiveNotification, object: nil, queue: .main) { _ inself.isActive = 真})观察者.追加(NotificationCenter.default.addObserver(forName: UIApplication.willResignActiveNotification, object: nil, queue: .main) { _ inself.isActive = false})}去初始化{观察者.forEach(NotificationCenter.default.removeObserver)}}

您需要在 SceneDelegate 中创建它(仅一次)并作为 @EnvironmentObject 传递给 ContentView:

让 appState = AppState()让 contentView = ContentView().environmentObject(appState)

现在你可以在任何你想要的视图中使用@EnvironmentObject:

struct FirstView: View {@EnvironmentObject var appState: AppStatevar主体:一些视图{文本(第一个视图，isActive:\(appState.isActive.description)")}}

I'm currently developing an application using SwiftUI.

I want to use a method when a view appears.

In the case of the code I attached below, I can use the print method when the app is booted and done some transitions between pages.

---

But I want to use the print method when I reopen the app like below:

• 1: run the code on a simulator (I can see the print method works).

• 2: press a home button.

• 3: open the app with tap the app icon (I can't see the print method works ).

  (*) I want to use the print method here.

How can I do it as I want in this case?

---

here is the code:

import SwiftUI

struct ContentView: View {
    
    @State private var selection = 0
 
    var body: some View {
        TabView(selection: $selection){
            Text("First View")
                .onAppear(){
                    print("First")
            }
                .tabItem {
                        Text("First")
                }
                .tag(0)
            
            Text("Second View")
                .tabItem {
                        Text("Second")
                }
                .tag(1)
        }
    }
}

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

---

ADD:

I found a way to use some function when the app becomes a foreground from a background using sceneWillEnterForeground or sceneWillResignActive in SceneDelegate.swift

But in this case, when the app becomes a foreground with the SecondView also works function. And I want to modify the code to work the function only when the app becomes foreground with the FirstView.

Is there any way to do that?

SceneDelegate.swift

func sceneDidBecomeActive(_ scene: UIScene) {
        print("BecomeActive")
    }
func sceneWillEnterForeground(_ scene: UIScene) {
        print("Foreground")
    }

---

Xcode: Version 11.7

Swift: Swift 5

解决方案

You may use an @EnvironmentObject to track the application state (by observing notifications):

class AppState: ObservableObject {
    @Published var isActive = true

    private var observers = [NSObjectProtocol]()

    init() {
        observers.append(
            NotificationCenter.default.addObserver(forName: UIApplication.didBecomeActiveNotification, object: nil, queue: .main) { _ in
                self.isActive = true
            }
        )
        observers.append(
            NotificationCenter.default.addObserver(forName: UIApplication.willResignActiveNotification, object: nil, queue: .main) { _ in
                self.isActive = false
            }
        )
    }
    
    deinit {
        observers.forEach(NotificationCenter.default.removeObserver)
    }
}

You need to create this (once only) in the SceneDelegate and pass to the ContentView as an @EnvironmentObject:

let appState = AppState()
let contentView = ContentView().environmentObject(appState)

Now you can use the @EnvironmentObject in any view you want:

struct FirstView: View {
    @EnvironmentObject var appState: AppState

    var body: some View {
        Text("First View, isActive: \(appState.isActive.description)")
    }
}

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