Unity.swift

class Unity: UnityFrameworkListener {
    static let shared = Unity()
    private let unityFramework: UnityFramework
    var view: UIView { unityFramework.appController()!.window }
    
    override init() {
        let frameworkPath = Bundle.main.bundlePath.appending("/Frameworks/UnityFramework.framework")
        let bundle = Bundle(path: frameworkPath)!
        unityFramework = bundle.principalClass!.getInstance()
        super.init()
    }
    
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) {
        unityFramework.register(self)
        NSClassFromString("FrameworkLibAPI")?.registerAPIforNativeCalls(self)
        unityFramework.setDataBundleId("com.unity3d.framework")
        unityFramework.runEmbedded(withArgc: CommandLine.argc, argv: CommandLine.unsafeArgv, appLaunchOpts: launchOptions)
        unityFramework.showUnityWindow()
    }
  }

/// 起動直後に呼ぶやつ
extension AppDelegate {
    func setupUnity(_ application: UIApplication, launchOptions: [UIApplication.LaunchOptionsKey: Any]?) {
        let window = UIApplication.shared.findKeyWindow()
        Unity.shared.application(application, didFinishLaunchingWithOptions: launchOptions)
        window?.makeKeyAndVisible()
    }
}

showUnityWindowを呼ぶ必要があるので、読んですぐに元々のkeyWindowに戻す。
あとは任意のタイミングでUnity.shared.viewを適当な場所にaddSubViewする