ios - 如何在Swift中将KVO用于UserDefaults？

我正在重写应用程序的各个部分，并找到以下代码:

fileprivate let defaults = UserDefaults.standard

func storeValue(_ value: AnyObject, forKey key:String) {
    defaults.set(value, forKey: key)
    defaults.synchronize()

    NotificationCenter.default.post(name: Notification.Name(rawValue: "persistanceServiceValueChangedNotification"), object: key)
}
func getValueForKey(_ key:String, defaultValue:AnyObject? = nil) -> AnyObject? {
    return defaults.object(forKey: key) as AnyObject? ?? defaultValue
}

当CMD单击defaults.synchronize()行时，我看到synchronize计划已弃用。这是用代码编写的:

/*!
     -synchronize is deprecated and will be marked with the NS_DEPRECATED macro in a future release.

     -synchronize blocks the calling thread until all in-progress set operations have completed. This is no longer necessary. Replacements for previous uses of -synchronize depend on what the intent of calling synchronize was. If you synchronized...
     - ...before reading in order to fetch updated values: remove the synchronize call
     - ...after writing in order to notify another program to read: the other program can use KVO to observe the default without needing to notify
     - ...before exiting in a non-app (command line tool, agent, or daemon) process: call CFPreferencesAppSynchronize(kCFPreferencesCurrentApplication)
     - ...for any other reason: remove the synchronize call
     */

据我所能解释的，我的用法符合第二种描述:写后同步，以便通知其他人。

它建议使用KVO进行观察，但是如何？当我搜索此内容时，我发现了一堆稍旧的Objective-C示例。遵守UserDefaults的最佳做法是什么？

最佳答案

从iOS 11 + Swift 4开始，推荐的方式(根据SwiftLint)是使用基于块的KVO API。

示例:

假设我有一个存储在用户默认值中的整数值，它称为greetingsCount。

首先，我需要扩展UserDefaults:

extension UserDefaults {
    @objc dynamic var greetingsCount: Int {
        return integer(forKey: "greetingsCount")
    }
}

这使我们以后可以定义观察的关键路径，如下所示:

var observer: NSKeyValueObservation?

init() {
    observer = UserDefaults.standard.observe(\.greetingsCount, options: [.initial, .new], changeHandler: { (defaults, change) in
        // your change logic here
    })
}

永远不要忘记清理:

deinit {
    observer?.invalidate()
}

关于ios - 如何在Swift中将KVO用于UserDefaults？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/43963220/