Why can't I assign value on didSet?

Question

I have two view. On my first view i create some data and send to other view lets name view2. So my view1 has code:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "showUserDetail" {
        (segue.destinationViewController as! UserDetailTableViewController).detailContact = detailCoversationContact
    }
}

In my detailCoversationContact i have detail about this one user, this detail like number, nick etc. Now as i expect this data are put to variable detailContact in my view2

And this is my cod in view2 this code is work:

class UserDetailTableViewController: UITableViewController {

@IBOutlet weak var nickNameLabel: UILabel!

var nickMy: String = ""

var detailContact: AnyObject? {
    didSet {
    // Update the user interface for the detail item.
        if let detail = self.detailContact {
            self.nickMy = (detail.valueForKey("nickName") as? String)!
        }
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    nickNameLabel.text = nickMy      
}

}

When i send data to detailContact ' i check is didSet if yes i set my nickMy and this is work. But what is first ? setting my var or viewDidLoad?

this is my code and not working and can someone explain why ?

class UserDetailTableViewController: UITableViewController {

    @IBOutlet weak var nickNameLabel: UILabel!

    var detailContact: AnyObject? {
        didSet {
        // Update the user interface for the detail item.
            if let detail = self.detailContact {
                   self.title = detail.valueForKey("nickName") as? String
                   self.nickNameLabel?.text = (detail.valueForKey("nickName") as? String)!
            }
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
    }

}

Ok this is self.title and work i see the name of user but title is from tableView. But my nickNameLabel is not change ? why ?

Answer 1

At the time of prepareForSegue , the IBOutlet s have not been set up yet. So, self.nickNameLabel is still nil , and optional chaining makes self.nickNameLabel?.text = ... safely do nothing.

Set the value in viewDidLoad() when the IBOutlet s have been set up:

override func viewDidLoad() {
    super.viewDidLoad()
    self.nickNameLabel?.text = (detail.valueForKey("nickName") as? String)!
}

Alternatively, you can trigger didSet by setting the detailContact to itself in viewDidLoad() . You have to trick Swift in order to do this because it thinks assigning detailContact to itself does nothing:

override func viewDidLoad() {
    super.viewDidLoad()
    detailContact = (detailContact)  // trigger didSet to set up the label
}