ios - 如何使用通知和观察者从另一个 UIViewController 隐藏 UILabel

Question

我有 2 个 UIViewControllers，我尝试使用 Notifications 和 观察者。 这是我第一次使用这种设计模式，我有点困惑。我做错了什么？ 我想指定只有当我从第二个 ViewController 单击后退按钮时，我才第一次从该打印中获取消息。 之后，当我单击 Go Next 时，消息正常，但 UILabel 没有隐藏或颜色改变。

这是我的第一个 UIViewController 代码:

class ReviewPhotosVC: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        NotificationCenter.default.post(name: Notification.Name("NotificationOfReviewMode"), object: nil)
    }

    @IBAction func goNextTapped(_ sender: UIButton) {

        let fullscreenVC = storyboard?.instantiateViewController(withIdentifier: "FullscreenPhoto") as! FullscreenPhotoVC

        self.present(fullscreenVC, animated: true, completion: nil)
    }
}

这是我的第二个 UIViewController 代码:

class FullscreenPhotoVC: UIViewController {

    @IBOutlet weak var customLabel: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        NotificationCenter.default.addObserver(self,
                                               selector: #selector(hideCustomLabel),
                                               name: Notification.Name("NotificationOfReviewMode"),
                                               object: nil)
    }

    @IBAction func goBackTapped(_ sender: UIButton) {

        let reviewPhotosVC = storyboard?.instantiateViewController(withIdentifier: "ReviewPhotos") as! ReviewPhotosVC

        self.present(reviewPhotosVC, animated: true, completion: nil)
    }

    @objc func hideCustomLabel(){

        customLabel.isHidden = true
        customLabel.textColor = .red
        print("My func was executed.")
    }
}

这是我的 Storyboard:

感谢您阅读本文。

Answer 1

问题是您在下一个 Controller 初始化并开始观察之前发布通知。此外，不需要通知，您可以直接进行。在这种情况下，我使用了一个额外的变量 shouldHideLabel 因为你不能直接调用函数 hideCustomLabel() 因为这会导致崩溃，因为 socket 只在 View 加载后初始化.

class ReviewPhotosVC: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        //NotificationCenter.default.post(name: Notification.Name("NotificationOfReviewMode"), object: nil)
    }

    @IBAction func goNextTapped(_ sender: UIButton) {

        let fullscreenVC = storyboard?.instantiateViewController(withIdentifier: "FullscreenPhoto") as! FullscreenPhotoVC
        fullscreenVC.shouldHideLabel = true
        self.present(fullscreenVC, animated: true, completion: nil)
    }
}

class FullscreenPhotoVC: UIViewController {

    var shouldHideLabel = false

    @IBOutlet weak var customLabel: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        if shouldHideLabel {
            hideCustomLabel()
        }
        /*
        NotificationCenter.default.addObserver(self,
                                               selector: #selector(hideCustomLabel),
                                               name: Notification.Name("NotificationOfReviewMode"),
                                               object: nil)
        */
    }

    @IBAction func goBackTapped(_ sender: UIButton) {
        self.dismiss(animated: true, completion: nil)
    }

    @objc func hideCustomLabel() {
        customLabel.isHidden = true
        customLabel.textColor = .red
        print("My func was executed.")
    }
}