iOS14中UIHostingController嵌套的SwiftUI视图无法弹出Alert的解决办法？

在iOS14环境下，嵌套在UIKit的UIHostingController中的SwiftUI视图使用.alert(isPresented:)无法弹出弹窗，本质原因是iOS14的UIHostingController未正确传递presentationMode环境值，导致SwiftUI内置的Alert依赖的弹出逻辑失效。以下是几种可行的解决办法：

方法1：手动注入presentationMode环境值 #

在创建UIHostingController时，给SwiftUI根视图手动注入presentationMode环境变量，确保Alert能获取到正确的弹出上下文：

// 创建SwiftUI视图
let contentView = ContentView()
// 初始化HostingController
let hostingController = UIHostingController(rootView: contentView)
// 手动注入presentationMode环境值
let presentationMode = PresentationMode(
    dismiss: { hostingController.dismiss(animated: true) }
)
hostingController.rootView = hostingController.rootView
    .environment(\.presentationMode, .init(wrappedValue: presentationMode))

方法2：通过闭包回调到UIKit层弹出Alert #

在SwiftUI视图中定义回调闭包，将弹出Alert的逻辑交给外层的UIKit控制器处理，完全绕过SwiftUI的Alert限制：

修改SwiftUI视图 #

struct ContentView: View {
    // 定义弹出Alert的回调闭包
    let showAlert: () -> Void
    
    var body: some View {
        VStack {
            Button("Delete") {
                showAlert()
            }
            Spacer()
        }.padding()
    }
}

在UIKit层处理弹出 #

// 创建ContentView时传入回调
let contentView = ContentView { [weak self] in
    guard let self = self else { return }
    let alert = UIAlertController(title: "Are you sure?", message: nil, preferredStyle: .alert)
    alert.addAction(UIAlertAction(title: "OK", style: .default))
    self.present(alert, animated: true)
}
// 初始化HostingController
let hostingController = UIHostingController(rootView: contentView)

方法3：封装UIKit的UIAlertController为SwiftUI组件 #

自定义一个UIViewControllerRepresentable组件，封装UIKit的UIAlertController，在SwiftUI视图中直接使用，兼容iOS14及以上版本：

封装UIKitAlert组件 #

struct UIKitAlert: UIViewControllerRepresentable {
    @Binding var isPresented: Bool
    let title: String
    
    func makeUIViewController(context: Context) -> UIAlertController {
        let alert = UIAlertController(title: title, message: nil, preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: "OK", style: .default) { _ in
            isPresented = false
        })
        return alert
    }
    
    func updateUIViewController(_ uiViewController: UIAlertController, context: Context) {
        // 根据isPresented状态控制弹窗的显示/隐藏
        if isPresented, uiViewController.presentingViewController == nil {
            context.coordinator.parent?.present(uiViewController, animated: true)
        } else if !isPresented, uiViewController.presentingViewController != nil {
            uiViewController.dismiss(animated: true)
        }
    }
    
    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }
    
    class Coordinator: NSObject {
        weak var parent: UIViewController?
        let alert: UIKitAlert
        
        init(_ alert: UIKitAlert) {
            self.alert = alert
            super.init()
        }
        
        override func didMoveToParent(_ parent: UIViewController?) {
            self.parent = parent
        }
    }
}

在SwiftUI视图中使用 #

struct ContentView: View {
    @State private var presentAlert = false
    
    var body: some View {
        VStack {
            Button("Delete") {
                presentAlert = true
            }
            Spacer()
        }
        .padding()
        // 添加封装的UIKitAlert组件
        .background(UIKitAlert(isPresented: $presentAlert, title: "Are you sure?"))
    }
}

内容的提问来源于stack exchange，提问作者andrew