CODEWITHSUNDEEP
iosswift
rusty
rusty

Reputation: 417

Using A Delegate to Pass a var

I have been pulling my hair out trying to get this 'Delegate' thing to work in Swift for an App I am working on.

I have two files: CreateEvent.swift and ContactSelection.swift, where the former calls the latter.

CreateEvent's contents are:

class CreateEventViewController: UIViewController, ContactSelectionDelegate {

    /...

    var contactSelection: ContactSelectionViewController = ContactSelectionViewController()

    override func viewDidLoad() {
        super.viewDidLoad()

        /...

        contactSelection.delegate = self
    }


    func updateInvitedUsers() {
        println("this finally worked")
    }

    func inviteButton(sender: AnyObject){
        invitedLabel.text = "Invite"
        invitedLabel.hidden = false
        toContactSelection()
    }

    /...

    func toContactSelection() {
        let contactSelection = self.storyboard?.instantiateViewControllerWithIdentifier("ContactSelectionViewController") as ContactSelectionViewController
        contactSelection.delegate = self
        self.navigationController?.pushViewController(contactSelection, animated: true)
    }

ContactSelection's contents are:

protocol ContactSelectionDelegate {
    func updateInvitedUsers()
}

class ContactSelectionViewController: UITableViewController {

    var delegate: ContactSelectionDelegate?

    override func viewDidLoad() {
        super.viewDidLoad()

        self.delegate?.updateInvitedUsers()

    }

    override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

    // Stuff

    self.delegate?.updateInvitedUsers()

    }
}

What am I doing wrong? I am still new and don't fully understand this subject but after scouring the Internet I can't seem to find an answer. I use the Back button available in the Navigation Bar to return to my CreateEvent view.

Upvotes: 0

Views: 87

Answers (1)

jrturton
jrturton

Reputation: 119242

var contactSelection: ContactSelectionViewController = ContactSelectionViewController()

This is instantiating a view controller directly, and the value never gets used. Since it looks like you're using storyboards, this isn't a good idea since none of the outlets will be connected and you'll get optional unwrapping crashes. You set the delegate of this view controller but that's irrelevant as it doesn't get used.

It also isn't a good idea because if you do multiple pushes you'll be reusing the same view controller and this will eventually lead to bugs as you'll have leftover state from previous uses which might give you unexpected outcomes. It's better to create a new view controller to push each time.

In your code you're making a brand new contactSelection from the storyboard and pushing it without setting the delegate.

You need to set the delegate on the instance that you're pushing onto the navigation stack.

It's also helpful to pass back a reference in the delegate method which can be used to extract values, rather than relying on a separate reference in the var like you're doing.

So, I'd do the following:

  • Remove the var contactSelection
  • Add the delegate before pushing the new contactSelection object

  • Change the delegate method signature to this:

    protocol ContactSelectionDelegate {
    func updateInvitedUsers(contactSelection:ContactSelectionViewController)
}

  • Change your delegate calls to this:

    self.delegate?.updateInvitedUsers(self)

Upvotes: 2

Related Questions