如何在SwiftUI sheet中监听scenePhase变化触发操作

SwiftUI 中通过.sheet/.fullScreenCover弹出的模态视图、NavigationView/NavigationStack内压栈的子视图，默认不会自动继承父层级的scenePhase环境值，直接在这类子视图内通过@Environment(\.scenePhase)配合onChange监听状态，会出现应用切后台等场景变更时回调不触发的问题。

方案1：手动逐层透传环境值 #

在根视图读取scenePhase，弹出模态、跳转子页面时，手动通过.environment(\.scenePhase, scenePhase)把环境值注入给下级视图；如果存在多层级跳转，每一层都要保持透传，链路中断后深层视图将无法收到状态变更。
参考实现：

import SwiftUI

struct ContentView: View {
    @Environment (\.scenePhase) private var scenePhase
    var body: some View {
        Text("Hello, world!")
            .sheet(isPresented: .constant(true)) {
                SheetView()
                    .environment(\.scenePhase, scenePhase)
            }
    }
}

struct SheetView: View {
    @Environment (\.scenePhase) private var scenePhase
    var body: some View {
        NavigationView {
            NavigationLink("Show FirstDetailsView") {
                FirstDetailsView()
                    .environment(\.scenePhase, scenePhase)
            }
        }
    }
}

struct FirstDetailsView: View {
    @Environment (\.scenePhase) private var scenePhase
    var body: some View {
        NavigationLink("Show SecondDetailsView") {
            SecondDetailsView()
                .environment(\.scenePhase, scenePhase)
        }
        .onChange(of: scenePhase) { _ in
            print("scenePhase changed.")
        }
    }
}

struct SecondDetailsView: View {
    @Environment (\.scenePhase) private var scenePhase
    var body: some View {
        Text("This is SecondDetailsView")
    }
}

该方案缺点：页面层级较深时需要每一层手动注入，维护成本高，容易因漏传导致监听失效。

方案2：根视图统一监听+事件分发（推荐） #

直接在App根层级（App结构体的WindowGroup或最顶层根视图）监听scenePhase变化，通过NotificationCenter或全局状态管理器将事件分发到所有需要响应的页面，无需逐层透传环境值，适配所有模态、导航子页面场景。
参考实现：

import SwiftUI

// 定义场景变更全局通知
extension Notification.Name {
    static let appScenePhaseDidChange = Notification.Name("appScenePhaseDidChange")
}

@main
struct DemoApp: App {
    @Environment(\.scenePhase) private var scenePhase
    var body: some Scene {
        WindowGroup {
            ContentView()
                .onChange(of: scenePhase) { newPhase in
                    // 全局分发场景变更事件
                    NotificationCenter.default.post(
                        name: .appScenePhaseDidChange,
                        object: newPhase
                    )
                }
        }
    }
}

struct ContentView: View {
    var body: some View {
        Text("Hello, world!")
            .sheet(isPresented: .constant(true), content: SheetView.init)
    }
}

struct SheetView: View {
    @State private var isFolderLocked = true
    var body: some View {
        Text("Hello, world!")
            .onAppear {
                print("view appeared.")
                // 文件夹锁定时触发认证、解锁逻辑
            }
            // 直接监听全局通知即可，无需透传环境值
            .onReceive(NotificationCenter.default.publisher(for: .appScenePhaseDidChange)) { output in
                guard let newPhase = output.object as? ScenePhase else { return }
                print("scenePhase changed.")
                if newPhase == .background {
                    // 进入后台时锁定文件夹
                    isFolderLocked = true
                }
            }
    }
}

适配提示：iPadOS 多窗口场景下使用该方案时，需要额外判断事件对应的窗口实例，避免多窗口状态串扰；单窗口iPhone应用可直接使用上述逻辑。

内容的提问来源于stack exchange，提问作者Fawzi Rifai