Cannot add String to Array for PFUser

Question

I have a button that pushes to a feed, I would like to record the name of the Feed Item in an array ("itemChosen") in my PFUser class every time the button is clicked:

@IBAction func buttonTapped(sender: UIButton) {

        PFUser.currentUser()!.addObject(feedItem.feedItemName, forKey: "itemChosen")
        PFUser.currentUser()!.saveInBackgroundWithBlock({ (success: Bool, error: NSError?) -> Void in
            println(PFUser.currentUser()?.objectForKey("itemChosen"))
        })
}

I get the error:

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Operation is invalid after previous operation.'

If I use:

PFUser.currentUser()!.setObject(feedItem.feedItemName, forKey: "itemChosen")

I can save the name as a singular String, but I want to append it into an array. Why doesn't addObject work and how can I fix it?

Answer 1

Try doing this:

@IBAction func buttonTapped(sender: UIButton) {
    if PFUser.currentUser()!["itemChosen"] == nil { PFUser.currentUser()!["itemChosen"] = [String]() }
    (PFUser.currentUser()!["itemChosen"] as! NSMutableArray).addObject(feedItem.feedItemName)
    PFUser.currentUser()!.saveInBackgroundWithBlock({ (success: Bool, error: NSError?) -> Void in
        println(PFUser.currentUser()?.objectForKey("itemChosen"))
    })
}

The problem is that PFUser.currentUser!["itemChosen"] can be nil.

Edit: I found a way to do it using Xcode 6:

extension PFUser {
    var param: [String] {
        get {
            if let x = self["itemChosen"] as? [String] {
                return x
            } else {
                return []
            }
        }
        set(val) {
            self["itemChosen"] = val
        }
    }
}

@IBAction func buttonTapped(sender: UIButton) {
    PFUser.currentUser()!.param.append(feedItem.feedItemName)
    PFUser.currentUser()!.saveInBackgroundWithBlock({ (success: Bool, error: NSError?) -> Void in
        println(PFUser.currentUser()?.objectForKey("itemChosen"))
    })
}