如何在Swift中使用UserDefaults的KVO？
如何在Swift中使用UserDefaults的KVO？
提问于 2017-05-14 19:13:29
我正在重写应用程序的一部分，发现了以下代码：
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
}按住CMD键并单击行defaults.synchronize()时，我看到synchronize已计划弃用。这是在代码中编写的：
/*!
-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
*/据我所知，我的用法符合第二种描述:写完后同步，以便通知其他人。
它建议使用KVO进行排卵，但如何进行呢？当我搜索这个的时候，我发现了一堆稍微老一点的Objective-C示例。观察UserDefaults的最佳实践是什么？
回答 1
Stack Overflow用户
发布于 2021-03-19 19:18:58
从iOS 13开始，现在有了一种更酷的方式来实现这一点，使用Combine：
import Foundation
import Combine
extension UserDefaults {
/// Observe UserDefaults for changes at the supplied KeyPath.
///
/// Note: first, extend UserDefaults with an `@objc dynamic` variable
/// to create a KeyPath.
///
/// - Parameters:
/// - keyPath: the KeyPath to observe for changes.
/// - handler: closure to run when/if the value changes.
public func observe<T>(
_ keyPath: KeyPath<UserDefaults, T>,
handler: @escaping (T) -> Void)
{
let subscriber = Subscribers.Sink<T, Never> { _ in }
receiveValue: { newValue in
handler(newValue)
}
self.publisher(for: keyPath, options: [.initial, .new])
.subscribe(subscriber)
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/43963220
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