Swift - How to set a singleton to nil

问题:

I am writing an app in swift and use a singleton to share a class object, User, across the app. I want to be able to set this singleton to 'nil' when the user logs out, so that when they log back in the old properties no longer exists (i.e. name, username, etc). I am hoping there is an easy way to just set the singleton back to nil, instead of having to set each property to nil.

Here is my User class that is used in the app as User.activeUser:

class User: NSObject
{
    class var activeUser : User? {
        struct Static {
            static let instance : User = User()
        }
        return Static.instance
    }
}

How can I change this so that the below code does not give me a warning and actually nils out the singleton object:

User.activeUser = nil

回答1:

This should work:

private var _SingletonSharedInstance:MyClass! = MyClass()

class MyClass {
  let prop = "test"

  class var sharedInstance : MyClass {
    return _SingletonSharedInstance
  }

  init () {}

  func destroy() {
    _SingletonSharedInstance = nil
  }
}

But then the references to the object are still kept, so you need to do some additional things to invalidate method calls in the class.

回答2:

Your activeUser is set up as a read-only computed property. Every time you call User.activeUser it is going to recompute the activeUser for you. In order to set it to nil you'll have to add some logic to determine whether or not a user is logged in outside of the computed property. Something like this would work:

class User: NSObject
{

    private struct userStatus { static var isLoggedIn: Bool = true }

    class var activeUser : User? {

        get {
            if userStatus.isLoggedIn {
                struct Static {
                    static let instance : User = User()
                }

                return Static.instance
            } else {
                return nil
            }
        }

        set(newUser) {
            if newUser != nil {
                userStatus.isLoggedIn = true
            } else {
                userStatus.isLoggedIn = false
            }
        }
    }
}