比较好的 UserDefaults 的用法

UserDefaultsExtension.swift

//https://developer.apple.com/videos/play/wwdc2019/212

extension UserDefaults {
    private static let isInfoBarHiddenKey = "IsInfoBarHidden"
    
    @objc dynamic var isInfoBarHidden: Bool {
        get { bool(forKey: UserDefaults.isInfoBarHiddenKey)  }
        set { set(newValue, forKey: UserDefaults.isInfoBarHiddenKey) }
    }
}

func testUserDefaults() {
    let _ = UserDefaults.standard.observe(\UserDefaults.isInfoBarHidden, options: .initial) { (_, value) in
        if let newValue = value.newValue {
            print(newValue)
        }
    }
}