说明

单例设计模式，方便的地方在于保持状态。弊端也在这里，比如用户已经注销，需要重置跟用户相关的信息。

单例重置对象解决

class Singleton {
    private static var privateShared: Singleton?
    
    let date = Date()
    
    class func shared() -> Singleton {
        guard let unwrapShared = privateShared else {
            privateShared = Singleton()
            return privateShared!
        }
        
        return unwrapShared
    }
    
    class func destroy() {
        privateShared = nil
    }
    
    func printDate() {
        let formatter = DateFormatter()
        formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
        let dateString = formatter.string(from: date)
        print("create Sigleton time > \(dateString)")
    }
    
    private init() {
        print("init singletion")
    }
    
    deinit {
        print("deinit singleton")
    }
}

运用如下

        Singleton.shared().printDate()
        DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(2)) {
            Singleton.shared().printDate()
        }
        DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(4)) {
            Singleton.destroy()
            Singleton.shared().printDate()
        }
        DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(6)) {
            Singleton.shared().printDate()
        }

打印结果

init singletion
create Sigleton time > 2020-04-09 09:16:26
create Sigleton time > 2020-04-09 09:16:26
deinit singleton
init singletion
create Sigleton time > 2020-04-09 09:16:30
create Sigleton time > 2020-04-09 09:16:30

参考

https://stackoverflow.com/questions/34046940/how-to-reset-singleton-instance

https://www.runoob.com/design-pattern/singleton-pattern.html