Issue to inherit UIAlertAction in Swift

Question

Here is my code:

class CustomAlertAction: UIAlertAction {
    init(title : String) {
        super.init(title: title, style: UIAlertActionStyle.Default) { (action) -> Void in
        }
    }
}

But I got the following compiling error:

Must call a designated initializer of the superclass 'UIAlertAction'

I know the designated initializer of UIAlertAction is init(). But the init(title, style, handler) of UIAlert will not call its designated initializer init()?

Any idea? Thanks

P.S.: Based on the Apple's document:

A designated initializer must call a designated initializer from its immediate superclass.”

Does this mean it's not allowed to inherit UIAlertAction in Swift? It's no problem to do so in Objective-C.

The reason why I want to create a subclass of UIAlertAction is because I want to add a ReactiveCocoa command as an action.

Answer 1

The solution is realistically almost certainly to use class extensions instead.

extension UIAlertAction {
    convenience init(title: String) {
        self.init(title: title, style: .Default, handler: nil)
    }
}

Usage:

let okayAction = UIAlertAction(title: "Okay")

---

You can still subclass the UIAlertAction to add properties to it. The subclass can still use this convience initializer you extended off of UIAlertAction class.

---

Finally, for what it's worth, someone has already created a Reactive Cocoa UIAlertAction subclass. They just did it in Objective-C. Seeing how there's no harm in adding Objective-C to your project, you could just take this approach... or just install that pod...

Answer 2

Like @nhgrif said, using an extension is the way to go. It's a complementary way to write expressiveness code.

Example:

/// App alert actions
extension UIAlertAction {
    static var cancel: UIAlertAction {
        return UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)
    }
    class func sharePhoto(handler: ((UIAlertAction) -> Void)?) -> UIAlertAction {
        return UIAlertAction(title: "Share", style: .Default, handler: handler)
    }
}

Use it like

alertController.addAction(.cancel)

alertController.addAction(.sharePhoto({ action in
    print(action)
}))