ios - 如果在初始化期间发布通知，则未收到通知？

Question

我创建了一个example project演示通知处理的同步性质。

通知按预期进行 - 模型初始化期间发布的通知除外。

The Swift Programming Language (Swift 4), Two-Phase Initialization部分解释了初始化的安全检查。在这里，它说:

Safety check 4
An initializer cannot call any instance methods, read the values of any instance properties, or refer to self as a value until after the first phase of initialization is complete.

在我的示例中，初始化的第一阶段在调用通知方法之前已完成。并且，如下所示，我还尝试直接调用通知。 View Controller 不会对两者进行操作 - 尽管在初始化之后调用时， View Controller 确实会按预期响应。

这是我应该报告的错误吗？或者我只是在一些关于初始化的简单事情上陷入了脑死亡？

以下是相关模型代码:

class Model {

    let notificationONEName = Notification.Name("NotificationONE")
    let notificationTWOName = Notification.Name("NotificationTWO")

    init() {
        notifyObserversTWO()
        NotificationCenter.default.post(name: notificationTWOName, object: self)
    }

    func notifyObserversONE() {
        print("START \(Model.self).\(#function)")
        NotificationCenter.default.post(name: notificationONEName, object: self)
        print("END \(Model.self).\(#function)")
    }
}

并且，这是 View Controller 中的观察者端代码:

import UIKit

class ViewController: UIViewController {

    let notificationONESelector = #selector(didReceiveNotificationONE)
    let notificationTWOSelector = #selector(didReceiveNotificationTWO)

    let model = Model()

    override func viewDidLoad() {
        super.viewDidLoad()

        subscribeToNotifications()
        model.notifyObserversONE()
        model.notifyObserversTWO()
    }

    func subscribeToNotifications() {
        NotificationCenter.default.addObserver(self,
                                           selector: notificationONESelector,
                                           name: model.notificationONEName,
                                           object: model)

        NotificationCenter.default.addObserver(self,
                                           selector: notificationTWOSelector,
                                           name: model.notificationTWOName,
                                           object: nil)
    }

    @objc func didReceiveNotificationONE(notification: Notification) {
        print("START \(ViewController.self).\(#function)")
        exampleUtilityFunction()
        print("END \(ViewController.self).\(#function)")
    }

    @objc func didReceiveNotificationTWO(notification: Notification) {
        print("START \(ViewController.self).\(#function)")
        exampleUtilityFunction()
        print("END \(ViewController.self).\(#function)")
    }

    func exampleUtilityFunction() {
        print("START \(ViewController.self).\(#function)")
        print("END \(ViewController.self).\(#function)")
    }
}

Answer 1

在调用 Model.init 时，没有任何东西在观察它。直到调用 Model() 很久之后才调用 subscribeToNotifications。

如果您想响应此通知，则首先需要在调用 init 之前观察 object: nil (与第二个通知相同)。这意味着您无法在属性定义中初始化它。您需要调用 subscribeToNotifications，然后创建 model。