Question

首先看看GIF：

第二页正在收听第一页上的操作。首先，第二页有状态：counter = 2和language = Chinese。但是当在第一页上按下按钮时，第二页的状态会更新。

我正在使用名为ReSwift的模块，如果您熟悉redux，则它是redux的Swift版本。但是，我想知道如何在不使用此模块的情况下完成此操作。（我不会问如何确切地了解GIF中发生的事情，但总的来说listen to updates/events on another page因此，我希望没有＆＃34; hacky＆＃34;解决方案）。

如果您对ReSwift方式感兴趣，请参阅以下代码

以下内容与此问题无关

Language.swift：

enum Language {
    case English
    case Chinese
}

LanguageState.swift：

import ReSwift

struct LanguageState: StateType {
    var language: Language = .English
}

CounterState.swift：

import ReSwift

struct CounterState: StateType {
    var counter: Int = 0
}

AppState.swift：

import ReSwift

struct AppState: StateType {
    var counterState: CounterState = CounterState()
    var languageState: LanguageState = LanguageState()
}

Actions.swift：

import ReSwift

struct CounterActionIncrease: Action {}
struct CounterActionDecrease: Action {}
struct ChangeLanguageToEnglish: Action {}
struct ChangeLanguageToChinese: Action {}

LanguageReducer.swift：

import ReSwift

func LanguageReducer(action: Action, state: LanguageState?) -> LanguageState {
    var state = state ?? LanguageState()

    switch action {
    case _ as ChangeLanguageToEnglish:
        state.language = .English
    case _ as ChangeLanguageToChinese:
        state.language = .Chinese
    default:
        break
    }

    return state
}

CounterReducer.swift：

import ReSwift

func CounterReducer(action: Action, state: CounterState?) -> CounterState {
    var state = state ?? CounterState()

    switch action {
    case _ as CounterActionIncrease:
        state.counter += 1
    case _ as CounterActionDecrease:
        state.counter -= 1
    default:
        break
    }

    return state
}

AppReducer.swift：

import ReSwift

func AppReducer(action: Action, state: AppState?) -> AppState {
    return AppState(
        counterState: CounterReducer(action: action, state: state?.counterState),
        languageState: LanguageReducer(action: action, state: state?.languageState)
    )
}

然后，在AppDelegate.swift：

中

import UIKit
import ReSwift

let store = Store<AppState>(reducer: AppReducer, state: nil)
...
...

最后，您可以以标准方式订阅ViewControllers商店

Answer 1

只需将其插入Xcode游乐场即可查看其机械工作原理。如果它打印＆＃34; Slick daddy＆＃34;然后它就联系起来了。可能需要进行大量的微调，例如确保您只更新已更改的数据，但是，如果代表模式不是您的选择，则使用观察者是一个很好的选择。

class ControllerA {

    // use a data model for the view controller
    let dataModel = "Slick daddy"

    init() {
        postNoti()
    }

    // whenever a change is made, first update the data model and
    // then post a notification and attach the data model object
    func postNoti() {
        NotificationCenter.default.post(name: Notification.Name("slickDaddy"), object: dataModel)
    }

}

class ControllerB {

    init() {
        addObserver()
    }

    // add an observer for that notification
    func addObserver() {
        NotificationCenter.default.addObserver(self, selector: #selector(notificationHandler(_:)), name: Notification.Name("slickDaddy"), object: nil)
    }

    // handle the notification using the data model and make
    // the changes to the current controller
    @objc func notificationHandler(_ sender: Notification) {
        guard let model = sender.object else {
            return
        }
        print(model) // verifies it works
    }

}

let b = ControllerB()
let a = ControllerA()

// prints "Slick daddy"

Answer 2

您可以使用NotificationCenter来实现这一目标。首先，我们必须创建一个单例类，并创建一个全局变量didUpdateNotificationName，我们将用它来发布事件并订阅事件：

let didUpdateDataNotificationName = "didUpdateDataNotificationName"

class AppState {

    static var shared = AppState()

    private init(){
        self.counter = 0
        self.language = "English"
    }

    private (set) var counter: Int {
        didSet {
            NotificationCenter.default.post(name: NSNotification.Name(rawValue: didUpdateDataNotificationName), object: nil)
        }
    }
    private (set) var language: String {
        didSet {
            NotificationCenter.default.post(name: NSNotification.Name(rawValue: didUpdateDataNotificationName), object: nil)
        }
    }

    func update(counter: Int){
        self.counter = counter
    }

    func update(language: String){
        self.language = language
    }

}

之后，在每个UIViewController上，您可以添加更新的侦听器：

NotificationCenter.default.addObserver(
    self, 
    selector: #selector(updateView), 
    name: NSNotification.Name(rawValue: didUpdateDataNotificationName),
    object: nil)

同时确保实现将在每个通知上执行的方法，在我们的案例中updateView：

@objc func updateView(){
    label.text = "\(DataModel.shared.counter) \(DataModel.shared.language)"

}

现在，每次更新AppState类中的变量时，都会向所有观察者发送通知。

一个非常重要的注意事项是，当您处理通知时，应该在不再需要时删除观察者。例如，在您班级的deinit方法中：

deinit {
    NotificationCenter.default.removeObserver(
        self, 
        name: NSNotification.Name(rawValue: didUpdateDataNotificationName),
        object: self)
}

Answer 3

如果是UITabBarController，您只需使用以下代码即可访问FirtsViewController中的SecondViewController

var svc:SecondViewController = self.tabBarController.viewControllers[1] as SecondViewController!

如何在Swift的另一个屏幕上收听更新？

3 个答案: