Question

我有一个NewCartViewController嵌入UINavigationController

在我的ContainerViewController中：

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "goToCart" {
        self.cartVC = segue.destination as? NewCartViewController
        self.cartVC?.delegate = self

        print("cartVC Delegate", cartVC?.delegate) // value is NOT nil here

        let pendingCart = PendingCart(color: .blue)

        self.cartVC?.setupPaintOrder(cart: pendingCart)
    }
}

在我的NewCartViewController

protocol NewCartViewControllerDelegate: class {
    func vcDidFinishWithCancel(_ newCartViewController: NewCartViewController)
}

class NewCartViewController: UIViewController {

    weak var delegate: NewCartViewControllerDelegate?

    ....

    @objc func dismissVC() { // called from the leftBarButtonItem
        print(delegate) // nil
    }

我查看了其他相关的答案，但不确定此处发生了什么。任何帮助，将不胜感激。谢谢！

编辑-有关如何实例化VC的更多详细信息：

我的BuyButtonVC调用一个委托方法回到AddToCartContainerVC：

extension AddToCartContainerViewController: BuyButtonViewControllerDelegate {
    func buyButtonVCDidPressButton(_ vc: BuyButtonViewController) {
         performSegue(withIdentifier: "goToCart", sender: self)
    }
}

然后从上方的第一个代码块中触发prepare(for segue:)函数，我们在其中查看segue.destination并设置委托。

我在didSet中的委托人的NewCartViewController上有打印，并且看到委托已设置。

用户转到屏幕，再也不会像调用didSet那样再次调用nil。但是，当我尝试在第二个代码块中调用委托方法时，委托为nil

Answer 1

我尝试使用以下代码，但似乎工作正常。

很少有几次我们得到这种未知的行为，并且在卡住时感到沮丧。尝试清理构建并退出Xcode清除派生数据，然后再次执行。

class ContainerViewController: UIViewController, NewViewControllerDelegate {

    weak var cartVC: NewViewController?

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "goToCart" {
            self.cartVC = segue.destination as? NewViewController
            self.cartVC?.delegate = self

            print("cartVC Delegate", cartVC?.delegate) // value is NOT nil here

//            let pendingCart = PendingCart(color: .blue)

//            self.cartVC?.setupPaintOrder(cart: pendingCart)
        }
    }

    func vcDidFinishWithCancel(_ newViewController: NewViewController) {
        print(newViewController.delegate)
        self.navigationController?.popViewController(animated: true)
    }

}

protocol NewViewControllerDelegate: class {
    func vcDidFinishWithCancel(_ newViewController: NewViewController)
}


class NewViewController: UIViewController {

    weak var delegate: NewViewControllerDelegate?

    @IBOutlet weak var leftBarButtonItem: UIBarButtonItem!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        navigationItem.leftBarButtonItem = UIBarButtonItem(title: "Cancel", style: .plain, target: self, action: #selector(dismissVC))
    }

    @objc func dismissVC() { // called from the leftBarButtonItem
        print(delegate) // nil
        delegate?.vcDidFinishWithCancel(self)
    }
}

输出：单击leftbarbuttonitem时

cartVC Delegate Optional(<NetworkExtensionTest.ViewController: 0x7f84c6d07670>)
Optional(<NetworkExtensionTest.ViewController: 0x7f84c6d07670>)
Optional(<NetworkExtensionTest.ViewController: 0x7f84c6d07670>)

代表将重置为零

1 个答案: