I am implementing a slide in style menu.

The menu is added as a child view controller on show, then animated into view. I then remove it from the view once it has been closed.

I would like to introduce a UIPanGestureRecognizer so the user can swipe it into view, however the logic for adding the view is only triggered when pressing open.

I'd like to avoid adding it many times and on every gesture, so I was thinking of checking if it was present, if not add it, then animate.

lazy var menuController = MenuController()

private var menuWidth: CGFloat = 300
private let keyWindow = UIApplication.shared.keyWindow

override func viewDidLoad() {
    super.viewDidLoad()

    setupNavigationItems()
    setupTableView()

    menuController.view.frame = CGRect(x: -menuWidth, y: 0, width: menuWidth, height: view.frame.height)

    let panGesture = UIPanGestureRecognizer(target: self, action: #selector(handlePan))
    view.addGestureRecognizer(panGesture)

}

@objc func handlePan(gesture: UIPanGestureRecognizer) {


    let translation = gesture.translation(in: view)
    let transform = CGAffineTransform(translationX: translation.x, y: 0)
    menuController.view.transform = transform
    navigationController?.view.transform = transform

}

@objc func handleOpen() {
    keyWindow?.addSubview(menuController.view)
    animateMenuController(transform: CGAffineTransform(translationX: self.menuWidth, y: 0)) { }

    addChild(menuController)

}

@objc func handleHide() {
    animateMenuController(transform: .identity) { [weak self] in
        self?.menuController.view.removeFromSuperview()
        self?.menuController.removeFromParent()
    }
}

I was hoping to do something like this

    @objc func handlePan(gesture: UIPanGestureRecognizer) {

        if view.subviews.contains(MenuController) {
            print("yes")
        }


        let translation = gesture.translation(in: view)
        let transform = CGAffineTransform(translationX: translation.x, y: 0)
        menuController.view.transform = transform
        navigationController?.view.transform = transform

    }

But this is not correct.