Swift View 似乎延迟加载到窗口层次结构中

Question

发生了一件非常奇怪的事情，似乎我的初始 View Controller 已加载，执行其逻辑，并且除了实际 View 本身之外的所有内容都没有添加到层次结构中，直到其他一切发生为止。

    protocol OnboardDisplayLogic: class
{
    func handleUserConfirmation(viewModel: OnboardModels.CheckForUser.ViewModel)
}

class OnboardViewController: UIViewController, OnboardDisplayLogic {

    var interactor: OnboardInteractor?
    var router: (NSObjectProtocol & OnboardRoutingLogic & OnboardDataPassing)?

    override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
        super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
        setup()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setup()
    }

    //MARK: Setup

    private func setup() {
        let viewController = self
        let interactor = OnboardInteractor()
        let presenter = OnboardPresenter()
        let router = OnboardRouter()
        viewController.interactor = interactor
        viewController.router = router
        interactor.presenter = presenter
        presenter.viewController = viewController
        router.viewController = viewController
        router.dataStore = interactor
    }

    private func setupView() {
        view.backgroundColor = UIColor.brown
    }

    //MARK: Routing

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if let scene = segue.identifier {
            let selector = NSSelectorFromString("routeTo\(scene)WithSegue:")
            if let router = router, router.responds(to: selector) {
                router.perform(selector, with: segue)
            }
        }
    }

    //MARK: View lifecycle
    override func viewDidLoad() {
        super.viewDidLoad()

        setupView()
        interactor?.checkForUser()
    }

    func handleUserConfirmation(viewModel: OnboardModels.CheckForUser.ViewModel) {
        if let username = viewModel.username {
            print("Logged in user: \(username)")
            router?.routeToUserFeed(segue: nil)
        } else {
            print("No user logged in")
            router?.routeToLoginRegister(segue: nil)
        }
    }

我认为它延迟的原因是，虽然我已将 View 背景颜色设置为棕色，但在 print("user notlogin") 代码中使用断点，我将其打印到控制台，因为交互器确定没有用户登录，但 View 保持白色。直到我跨过去并完成所有代码的运行后，屏幕才会变成棕色。

因此我收到错误

Warning: Attempt to present ... whose view is not in the window hierarchy!

因为某些东西阻止 View 添加到最后。

Answer 1

实际 View 在进入 View Controller 生命周期之前不会加载。如果您需要在将 View 添加到 super View 的层次结构之前将其加载到设置中，只需使用 View 的 getter (let _ = viewController.view)。

UIViewController也有loadView()方法，查看:Apple documentation .

我们在使用 Clean Swift 时也遇到过此类问题。正确的工作方式是从 Storyboard实例化并仅使用正常的 segues/生命周期，就像 MVC 对 Apple 示例所做的那样。

您应该从 Storyboard实例化 let viewControllerToPush = Storyboard?.instantiate... 并使用该 View Controller ，而不是执行 let viewControllerToPush = MyVCSublass(...) .