Method cannot be marked @objc because the type of the parameter 2 cannot be represented in Objective-C [duplicate]

Question

After I have updated Swift 1 to Swift 2.0 I have an issue.

I am getting the following error on the first line of this code:

Method cannot be marked @objc because the type of the parameter cannot be represented in Objective-C

@objc func personsToFirstStep(persons: [Person]) {
    for person in persons {
        if !self.persons.contains(person) && person.id != userID {
            self.persons.append(person)
        }
    }

    collectionView.reloadData()
    collectionViewPlaceholder.hidden = true
    collectionView.hidden = false
    collectionGradientView.hidden = false
} 

This this Person class:

class Person: Hashable {

    var intID: Int = 0
    var id: String = ""
    var name: String = ""
    var type: String = ""

    var hashValue: Int {
        return self.intID
    }

    init(id: String, name: String, type: String) {
        self.id = id
        self.intID = Int(id)!
        self.name = name
        self.type = type
    }

}

func ==(lhs: Person, rhs: Person) -> Bool {
    return lhs.intID == rhs.intID
}

Answer 1

You have very nicely explained the problem yourself:

class Person: Hashable {

Person is not an NSObject. But only an NSObject-derived class type can be seen by Objective-C. Therefore your Person type is invisible to Objective-C. But your @objc func declaration is for a function that takes an array of Person — and we have just said that Person is invisible to Objective-C. So your @objc func declaration is illegal. Objective-C cannot be shown this function, because it cannot be shown its parameter.

You would need to change your class declaration to start like this:

class Person: NSObject {

...and then you might of course have to make any necessary further adjustments in the class's implementation. But that change would make your @objc func declaration legal. (NSObject is Hashable, so the amount of work needed to make this adaptation might not be very great.)

Answer 2

I was getting this because I declared a class Notification of my own and it was messing with Foundation's Notification class.

@objc func playerItemDidReachEnd(notification: Notification) {...}

So I changed it to Foundation.Notification

@objc func playerItemDidReachEnd(notification: Foundation.Notification) {...}