如果在 init 期间发布，则未收到通知？

Question

我创建了一个 example project 来演示 Notification 处理的同步性质。

通知按预期进行 - 除了在模型初始化期间发布的通知。

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.

初始化的第一阶段在我的示例中在调用通知方法之前完成。而且，如下图，我也试过直接调用通知。视图控制器都没有采取任何行动 - 尽管在 初始化后 调用时，视图控制器确实按预期响应。

这是我应该报告的错误吗？还是我只是在一些简单的初始化问题上脑残了？

相关型号代码如下：

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)")
    }
}

而且，这是视图控制器中的观察者端代码：

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 Model.init 被调用时，没有任何东西在观察它。在调用 Model().

很久之后才调用 subscribeToNotifications

如果您想回复此通知，您首先需要在调用 init 之前观察 object: nil（就像您对第二个通知所做的那样）。这意味着您不能在 属性 定义中对其进行初始化。您需要调用 subscribeToNotifications 然后创建 model.