Swift 4中的KVO侦听器问题 [英] KVO listener issues in Swift 4

问题描述

我正在使用ViewModel类，并且想要设置观察者(如果对loginResponse变量有任何更改).

I am using ViewModel class and want to setup observer if any changes into loginResponse variable.

@objcMembers class ViewModel: NSObject {

    var count = 300
    @objc dynamic var loginResponse :String

    override init() {
        loginResponse = "1"
        super.init()
        setupTimer()
    }

    func setupTimer(){
        _ = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector:#selector(callTimer), userInfo: nil, repeats: true)
    }

    func callTimer(){
        let minutes = String(count / 60)
        let seconds = String(count % 60)
        loginResponse = minutes + ":" + seconds
        count =  count - 1
    }
}

查看控制器代码:

override func viewDidLoad() {
    super.viewDidLoad()

    _ = viewModel.observe(\ViewModel.loginResponse) { (model, changes) in
        print(changes)
    }
}

我想在Viewcontroller中收听对loginResponse变量的任何更改，但是没有得到回调.我在这里做什么错了?

I want to listen to any change into loginResponse variable in my Viewcontroller but it's not getting the callback. What am I doing wrong here?

推荐答案

.observe(_:options:changeHandler:)函数返回一个NSKeyValueObservation对象，该对象用于控制观察的生存期.当它初始化或无效时，观察将停止.

The .observe(_:options:changeHandler:) function returns a NSKeyValueObservation object that is used to control the lifetime of the observation. When it is deinited or invalidated, the observation will stop.

由于您的视图控制器未保留对返回的观察"的引用，因此它在viewDidLoad末尾超出范围，因此停止观察.

Since your view controller doesn't keep a reference to the returned "observation" it goes out of scope at the end of viewDidLoad and thus stops observing.

要继续观察视图控制器的生命周期，请将返回的观察值存储在属性中.如果在此之前完成"观察，则可以在观察中调用invalidate或将属性设置为nil.

To continue observing for the lifetime of the view controller, store the returned observation in a property. If you're "done" observing before that, you can call invalidate on the observation or set the property to nil.

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