XcodeプロジェクトをSwiftUIを使って起動するようにマイグレーション

手順

AppDelegate.swift に以下を追加

    // MARK: UISceneSession Lifecycle

    func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
        // Called when a new scene session is being created.
        // Use this method to select a configuration to create the new scene with.
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
    }

    func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
        // Called when the user discards a scene session.
        // If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
        // Use this method to release any resources that were specific to the discarded scenes, as they will not return.
    }

SceneDelegate.swift を作成

import UIKit
import SwiftUI

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
        // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
        // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).

        // Use a UIHostingController as window root view controller
        if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
            window.rootViewController = UIHostingController(rootView: ContentView())
            self.window = window
            window.makeKeyAndVisible()
        }
    }

    func sceneDidDisconnect(_ scene: UIScene) {
        // Called as the scene is being released by the system.
        // This occurs shortly after the scene enters the background, or when its session is discarded.
        // Release any resources associated with this scene that can be re-created the next time the scene connects.
        // The scene may re-connect later, as its session was not neccessarily discarded (see `application:didDiscardSceneSessions` instead).
    }

    func sceneDidBecomeActive(_ scene: UIScene) {
        // Called when the scene has moved from an inactive state to an active state.
        // Use this method to restart any tasks that were paused (or not yet started) when the scene was inactive.
    }

    func sceneWillResignActive(_ scene: UIScene) {
        // Called when the scene will move from an active state to an inactive state.
        // This may occur due to temporary interruptions (ex. an incoming phone call).
    }

    func sceneWillEnterForeground(_ scene: UIScene) {
        // Called as the scene transitions from the background to the foreground.
        // Use this method to undo the changes made on entering the background.
    }

    func sceneDidEnterBackground(_ scene: UIScene) {
        // Called as the scene transitions from the foreground to the background.
        // Use this method to save data, release shared resources, and store enough scene-specific state information
        // to restore the scene back to its current state.
    }

}

起動画面となる ContentView.swift を作成

import SwiftUI

struct ContentView : View {
    var body: some View {
        Text("Hello World!")
    }
}

#if DEBUG
struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}
#endif

Info.plist に以下を追加

    <key>UIApplicationSceneManifest</key>
    <dict>
        <key>UIApplicationSupportsMultipleScenes</key>
        <false/>
        <key>UISceneConfigurations</key>
        <dict>
            <key>UIWindowSceneSessionRoleApplication</key>
            <array>
                <dict>
                    <key>UILaunchStoryboardName</key>
                    <string>LaunchScreen</string>
                    <key>UISceneConfigurationName</key>
                    <string>Default Configuration</string>
                    <key>UISceneDelegateClassName</key>
                    <string>$(PRODUCT_MODULE_NAME).SceneDelegate</string>
                </dict>
            </array>
        </dict>
    </dict>

環境

Xcode 11 beta 3

参考