iOS Delegation

Delegation in iOS

Displaying and Dismissing a Modal using Delegation

class ViewController: UIViewController, ModalViewDelegate {
    // Tapping the button displays the modal
    @IBAction func didTapButton(sender: UIButton) {
        let modal = ModalViewController()

        // Remember to set the delegate
        modal.delegate = self

        // Display the modal
        presentViewController(modal, animated: true, completion: nil)
    }

    func dismissModal(modal: ModalViewController?) {
        dismissViewControllerAnimated(true, completion: nil)
    }
}

// `class` indicates only classes may implement this protocol
protocol ModalViewDelegate: class {
    // Common practice is to pass the sender to the delegate
    func dismissModal(sender: ModalViewController?)
}

class ModalViewController: UIViewController {
    /*
        Use a weak reference so that this doesn't keep the delegate from
        being garbage collected.
    */
    weak var delegate: ModalViewDelegate?

    override func loadView() {
        // CGRectZero is equivalent to CGRectMake(0, 0, 0, 0)
        let view = UIView(frame: CGRectZero)

        view.backgroundColor = UIColor.redColor()
        let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(ModalViewController.didTap))
        view.addGestureRecognizer(tapGestureRecognizer)

        self.view = view
    }

    func didTap() {
        delegate?.dismissModal(self)
    }
}