只有类方法和委托的Swift类？

Question

I want a class with all class methods. I would like to use a delegate so my view controllers (conforming to the protocol) can call AlertFactory.passwordResetSucess() and display the alert.

1. Is there a way to make this this work? A way to use the delegate from this class?

2. Is this bad practice? Bad form? Why?

3. What's a good way to make this happen? There will be other class methods used in several views.

Thanks!

    protocol AlertFactoryDelegate 
    {
        func showAlert(alert: UIAlertController)
    }

    class AlertFactory: NSObject {

     let delegate: AlertFactoryDelegate!

     class func passwordResetSuccess() 
     {
         var alert = UIAlertController(title: "Success!", message: "Yay", preferredStyle: UIAlertControllerStyle.Alert)
         alert.addAction(UIAlertAction(title: "Continue", style: UIAlertActionStyle.Default, handler: nil))
         delegate.showAlert(alert)
     }
    }

Answer 1

You can set delegate to be static , and access it with AlertFactory.delegate

class AlertFactory: NSObject {
    static weak var delegate: AlertFactoryDelegate?

    class func passwordResetSuccess() {
        ...
        self.delegate?.showAlert(alert)
    }
}

To create a delegate:

class SomeClass: AlertFactoryDelegate {
    ... // Implement everything the protocol requires
}

// Asssing a delegate
AlertFactory.delegate = SomeClass()

Answer 2

1. You could use the SINGLETON command pattern, its a very common practice. You should read up on it, but basically means there is only 1 ever instance of it and you can call methods off of it when needed (or send things to it as needed). Common examples are EventSystem objects or GlobalObserver objects, Factories, and ContextManagers.

Here is information on it: https://sourcemaking.com/design_patterns/singleton

2. Using a SINGLETON has tradeoffs, but can be very useful in many situations. This seems like a good pattern for your problem.

3. You need to initialize your delegate when your app starts. From then on, when another view controller needs to set that delegate you can assign it: (this assumes you made delegate public and its a SINGLETON)

_myViewController.actionThatRequiresDelegate = AlertFactory.delegate

As mentioned in one of the other answers, using Swifts trailing syntax closure system is a great way to use anonymous functions and you could do your logic in there, or communicate with your delegate in there.

update

Initialize in the AppDelegate.swift:

override init()
{
    AlertFactory.init()
}

Then in your AlertFactory

public static AlertFactoryDelegate myDelegate

public static func init()
{
    myDelegate = new AlertFactoryDelegate()
}

Answer 3

You cannot set an instance variable on a class without instantiating the class first. Is there a reason you don't want to instantiate the class, and just want to use class methods instead? If you feel that you have good reason to use class methods over instance methods, then you have two potential options:

1. Pass a delegate as a parameter to the class method.
2. Use Completion Blocks instead of Delegation. Here's a decent example in swift.

In my personal experience I find blocks to be preferable.

EDIT: I haven't used Swift that much lately, but as @Skrundz pointed out you can indeed use a static variable on a class in Swift.