SwiftUI Alert with non declarative style.

NonDeclarativeAlert.swift

//
//  NonDeclarativeAlert.swift
//  MFileViewer
//
//  Created by yuki on 2025/02/25.
//

import SwiftUI

public struct AlertAction<Value> {
    let content: AnyView
    let role: ButtonRole?
    var value: Value
    
    public init<Content: View>(
        value: Value = (),
        role: ButtonRole? = nil,
        @ViewBuilder content: () -> Content
    ) {
        self.value = value
        self.role = role
        self.content = AnyView(content())
    }
    
    public init(
        _ titleKey: LocalizedStringKey,
        value: Value = (),
        role: ButtonRole? = nil
    ) {
        self.value = value
        self.role = role
        self.content = AnyView(Text(titleKey))
    }
}

// MARK: - Alert -

extension View {
    public func showAlert<ActionValue>(
        _ titleKey: LocalizedStringKey,
        message: LocalizedStringKey? = nil,
        @ArrayBuilder<AlertAction<ActionValue>> actions: () -> [AlertAction<ActionValue>]
    ) async -> ActionValue {
        await self.showAlert(
            titleKey,
            message: {
                if let message = message {
                    Text(message)
                } else {
                    EmptyView()
                }
            },
            actions: actions
        )
    }
    
    public func showAlert<Message: View, ActionValue>(
        _ titleKey: LocalizedStringKey,
        @ViewBuilder message: @escaping () -> Message,
        @ArrayBuilder<AlertAction<ActionValue>> actions: () -> [AlertAction<ActionValue>]
    ) async -> ActionValue {
        guard let topMostViewController = UIApplication.shared.topMostViewController() else {
            fatalError("Failed to get top most view controller")
        }
        
        return await withCheckedContinuation { continuation in
            var hostingVC: UIHostingController<ShowAlertView<Message, ActionValue>>!
            hostingVC = UIHostingController(
                rootView: ShowAlertView(
                    titleKey: titleKey,
                    message: message,
                    actions: actions(),
                    onDismiss: { value in
                        continuation.resume(returning: value)
                        hostingVC.removeFromParent()
                        hostingVC.view.removeFromSuperview()
                    }
                )
            )
            topMostViewController.addChild(hostingVC)
            topMostViewController.view.addSubview(hostingVC.view)
            NSLayoutConstraint.activate([
                hostingVC.view.topAnchor.constraint(equalTo: topMostViewController.view.topAnchor),
                hostingVC.view.leadingAnchor.constraint(equalTo: topMostViewController.view.leadingAnchor),
                hostingVC.view.heightAnchor.constraint(equalToConstant: 0),
                hostingVC.view.widthAnchor.constraint(equalToConstant: 0)
            ])
        }
    }
}

private struct ShowAlertView<Message: View, ActionValue>: View {
    let titleKey: LocalizedStringKey
    let message: () -> Message
    let actions: [AlertAction<ActionValue>]
    let onDismiss: (ActionValue) -> Void
    
    @State private var isPresented = true
    
    var body: some View {
        EmptyView()
            .alert(
                self.titleKey,
                isPresented: self.$isPresented,
                actions: {
                    ForEach(self.actions.indexed(), id: \.index) { (_, action) in
                        Button(role: action.role, action: {
                            self.onDismiss(action.value)
                        }) {
                            action.content
                        }
                    }
                },
                message: self.message
            )
    }
}

// MARK: - Alert with TextField -

extension View {
    public func showAlertWithTextField<ActionValue>(
        _ titleKey: LocalizedStringKey,
        message: LocalizedStringKey? = nil,
        prompt: LocalizedStringKey? = nil,
        initialValue: String = "",
        @ArrayBuilder<AlertAction<ActionValue>> actions: () -> [AlertAction<ActionValue>]
    ) async -> String? {
        await self.showAlertWithTextField(
            titleKey,
            message: {
                if let message = message {
                    Text(message)
                } else {
                    EmptyView()
                }
            },
            prompt: prompt,
            initialValue: initialValue,
            actions: actions
        )
        .text
    }
    
    public func showAlertWithTextField<Message: View, ActionValue>(
        _ titleKey: LocalizedStringKey,
        @ViewBuilder message: @escaping () -> Message,
        prompt: LocalizedStringKey? = nil,
        initialValue: String = "",
        @ArrayBuilder<AlertAction<ActionValue>> actions: () -> [AlertAction<ActionValue>]
    ) async -> String? {
        await self.showAlertWithTextField(
            titleKey,
            message: message,
            prompt: prompt,
            initialValue: initialValue,
            actions: actions
        )
        .text
    }
    
    public func showAlertWithTextField<ActionValue>(
        _ titleKey: LocalizedStringKey,
        message: LocalizedStringKey? = nil,
        prompt: LocalizedStringKey? = nil,
        initialValue: String = "",
        @ArrayBuilder<AlertAction<ActionValue>> actions: () -> [AlertAction<ActionValue>]
    ) async -> (value: ActionValue, text: String?) {
        await self.showAlertWithTextField(
            titleKey,
            message: {
                if let message = message {
                    Text(message)
                } else {
                    EmptyView()
                }
            },
            prompt: prompt,
            initialValue: initialValue,
            actions: actions
        )
    }
    
    public func showAlertWithTextField<Message: View, ActionValue>(
        _ titleKey: LocalizedStringKey,
        @ViewBuilder message: @escaping () -> Message,
        prompt: LocalizedStringKey? = nil,
        initialValue: String = "",
        @ArrayBuilder<AlertAction<ActionValue>> actions: () -> [AlertAction<ActionValue>]
    ) async -> (value: ActionValue, text: String?) {
        guard let topMostViewController = UIApplication.shared.topMostViewController() else {
            fatalError("Failed to get top most view controller")
        }
        
        return await withCheckedContinuation { continuation in
            var hostingVC: UIHostingController<ShowAlertWithTextFieldView<Message, ActionValue>>!
            hostingVC = UIHostingController(
                rootView: ShowAlertWithTextFieldView(
                    titleKey: titleKey,
                    message: message,
                    prompt: prompt,
                    initialValue: initialValue,
                    actions: actions(),
                    onDismiss: { actionValue, text in
                        continuation.resume(returning: (actionValue, text))
                        hostingVC.removeFromParent()
                        hostingVC.view.removeFromSuperview()
                    }
                )
            )
            topMostViewController.addChild(hostingVC)
            topMostViewController.view.addSubview(hostingVC.view)
            NSLayoutConstraint.activate([
                hostingVC.view.topAnchor.constraint(equalTo: topMostViewController.view.topAnchor),
                hostingVC.view.leadingAnchor.constraint(equalTo: topMostViewController.view.leadingAnchor),
                hostingVC.view.heightAnchor.constraint(equalToConstant: 0),
                hostingVC.view.widthAnchor.constraint(equalToConstant: 0)
            ])
        }
    }
}

private struct ShowAlertWithTextFieldView<Message: View, ActionValue>: View {
    let titleKey: LocalizedStringKey
    let message: () -> Message
    let prompt: LocalizedStringKey?
    let actions: [AlertAction<ActionValue>]
    let onDismiss: (ActionValue, String?) -> Void
    
    @State private var isPresented = true
    
    @State private var text: String
    
    init(
        titleKey: LocalizedStringKey,
        message: @escaping () -> Message,
        prompt: LocalizedStringKey?,
        initialValue: String,
        actions: [AlertAction<ActionValue>],
        onDismiss: @escaping (ActionValue, String?) -> Void
    ) {
        self.titleKey = titleKey
        self.message = message
        self.prompt = prompt
        self.actions = actions
        self.onDismiss = onDismiss
        self._text = State(initialValue: initialValue)
    }
    
    var body: some View {
        EmptyView()
            .alert(
                self.titleKey,
                isPresented: self.$isPresented,
                actions: {
                    TextField("", text: self.$text, prompt: self.prompt.map { Text($0) })
                    ForEach(self.actions.indexed(), id: \.index) { (_, action) in
                        Button(role: action.role, action: {
                            if action.role == .cancel {
                                self.onDismiss(action.value, nil)
                            } else {
                                self.onDismiss(action.value, self.text)
                            }
                        }) {
                            action.content
                        }
                    }
                },
                message: self.message
            )
    }
}


extension UIApplication {
    fileprivate func topMostViewController(
        base: UIViewController? = nil
    ) -> UIViewController? {
        let base = base ?? UIApplication.shared
            .connectedScenes
            .compactMap { $0 as? UIWindowScene }
            .flatMap { $0.windows }
            .first { $0.isKeyWindow }?
            .rootViewController
        
        if let nav = base as? UINavigationController {
            return topMostViewController(base: nav.visibleViewController)
        }
        if let tab = base as? UITabBarController,
           let selected = tab.selectedViewController {
            return topMostViewController(base: selected)
        }
        if let presented = base?.presentedViewController {
            return topMostViewController(base: presented)
        }
        return base
    }
}

Usage

SwiftUI alert with non declarative style. (Swift Concurrency style)

// reguler
let value: Int = await self.showAlert("Hello World") {
    AlertAction(value: 0) { Text("OK") }
    AlertAction(value: 1, role: .cancel) { Text("Cancel") }

    // or

    AlertAction("OK", value: 0)
    AlertAction("Cancel", value: 1, role: .cancel)
}

// with TextField
let value: String? = await self.showAlertWithTextField(
    "Account Name",
    message: "Enter your account name",
    prompt: "Account Name"
) {
    AlertAction("OK")
    AlertAction("Cancel", role: .cancel)
}