SwiftUI：APP回到前台时在任意视图上层展示验证视图

方案一：全局状态+自定义ViewModifier（纯SwiftUI方式） #

通过全局状态管理验证视图的显示状态，搭配自定义ViewModifier实现全局监听，避免重复写监听代码。

1. 全局状态管理类

import SwiftUI

class AppAuthenticationManager: ObservableObject {
    static let shared = AppAuthenticationManager()
    @Published var shouldShowAuthView = false
    
    private init() {
        // 监听进入后台，标记需要验证
        NotificationCenter.default.addObserver(self, selector: #selector(appEnteredBackground), name: UIApplication.didEnterBackgroundNotification, object: nil)
        // 监听回到前台，触发验证视图
        NotificationCenter.default.addObserver(self, selector: #selector(appEnteredForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
    }
    
    @objc private func appEnteredBackground() {
        shouldShowAuthView = true
    }
    
    @objc private func appEnteredForeground() {
        if shouldShowAuthView {
            DispatchQueue.main.async {
                self.shouldShowAuthView = true
            }
        }
    }
    
    // 验证完成后调用，重置状态
    func completeAuthentication() {
        shouldShowAuthView = false
    }
}

2. 自定义ViewModifier

struct AuthenticationViewModifier: ViewModifier {
    @ObservedObject var authManager = AppAuthenticationManager.shared
    
    func body(content: Content) -> some View {
        content
            .fullScreenCover(isPresented: $authManager.shouldShowAuthView) {
                FullCoverViewDidEnterBg()
                    .onDisappear {
                        authManager.completeAuthentication()
                    }
            }
    }
}

// 给View扩展，方便调用
extension View {
    func addAuthenticationCover() -> some View {
        self.modifier(AuthenticationViewModifier())
    }
}

3. 应用到视图中

@main
struct NavApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
                .addAuthenticationCover()
        }
    }
}

struct ContentView: View {
    @State var isPresenting = true
    var body: some View {
        NavigationStack {
            VStack {
                Button("Present Full Cover") {
                    isPresenting.toggle()
                }
                Text("Hello, world!")
            }
            .fullScreenCover(isPresented: $isPresenting) {
                FullCoverView()
                    .addAuthenticationCover() // 子全屏视图也要添加
            }
        }
    }
}

struct FullCoverView: View {
    @Environment(\.dismiss) var dismiss
    var body: some View {
        VStack {
            Text("FullCoverView")
            Button("dismiss") {
                dismiss()
            }
        }
    }
}

struct FullCoverViewDidEnterBg: View {
    @Environment(\.dismiss) var dismiss
    var body: some View {
        VStack {
            Text("请验证身份（面容ID/密码）")
            Button("验证完成") {
                dismiss()
            }
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .background(Color.white)
    }
}

方案二：借助UIKit获取顶层视图控制器（混合方式） #

直接通过UIKit获取当前顶层视图控制器，强制弹出验证视图，无需修改现有SwiftUI视图结构。

1. 扩展UIApplication获取顶层VC

import UIKit

extension UIApplication {
    func topViewController() -> UIViewController? {
        let keyWindow = connectedScenes
            .filter({$0.activationState == .foregroundActive})
            .map({$0 as? UIWindowScene})
            .compactMap({$0})
            .first?.windows
            .filter({$0.isKeyWindow}).first
        
        var topVC = keyWindow?.rootViewController
        while let presentedVC = topVC?.presentedViewController {
            topVC = presentedVC
        }
        return topVC
    }
}

2. 修改全局状态类，用UIKit弹出视图

class AppAuthenticationManager: ObservableObject {
    static let shared = AppAuthenticationManager()
    
    private init() {
        NotificationCenter.default.addObserver(self, selector: #selector(appEnteredForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
    }
    
    @objc private func appEnteredForeground() {
        guard let topVC = UIApplication.shared.topViewController() else { return }
        
        // 将SwiftUI视图包装成UIHostingController
        let authView = FullCoverViewDidEnterBg()
        let hostingVC = UIHostingController(rootView: authView)
        hostingVC.modalPresentationStyle = .fullScreen
        
        topVC.present(hostingVC, animated: true)
    }
}

3. 初始化管理器

@main
struct NavApp: App {
    let authManager = AppAuthenticationManager.shared
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

方案对比 #

• 纯SwiftUI方案：符合SwiftUI状态驱动理念，代码易维护，但需要给每个弹出的全屏视图添加Modifier。
• 混合UIKit方案：无需修改现有视图结构，全局强制弹出验证视图，适合已有较多页面的项目，但需要处理SwiftUI与UIKit的视图转换。

内容的提问来源于stack exchange，提问作者SomeCoder