Delegate Chaining Workaround October 2010 Kaz Yoshikawa 

About me 

Kaz Yoshikawa • Electricwoods LLC ୅ද / Digital Lynx Systems Inc. ෭୅ද • e-mail: [email protected] • twitter: @codelynx1 • Working History • Adobe Systems (Tokyo) • Lionbridge (Tokyo) • Quark (Tokyo / Denver) • Hummingbird Communications (Mt. View, USA) • Fact International (Vancouver, Canada) • Perle Systems (Toronto, Canada), etc. 

What is Delegate Chaining? 

Delegate Chaining Primary VC Secondary VC Primary VC Secondary VC Tertiary VC Quaternary VC Delegate Delegate Delegate Delegate • Simple delegate: • Chain of delegates: Method Invocation 

protocol SecondaryViewControllerDelegate: AnyObject { func save() } class PrimaryViewController: UIViewController, SecondaryViewControllerDelegate { func save() { // save } } class SecondaryViewController: UIViewController { weak var delegate: SecondaryViewControllerDelegate? @IBAction func save(_ sender: UIButton) { self.delegate?.save() } } Simple Delegate 

Delegate Chaining class PrimaryViewController: UIViewController, SecondaryViewControllerDelegate { func save() { // save } } class SecondaryViewController: UIViewController, TertiaryViewControllerDelegate { weak var delegate: SecondaryViewControllerDelegate? func save() { self.delegate?.save() } } class TertiaryViewController: UIViewController, QuaternaryViewControllerDelegate { weak var delegate: TertiaryViewController? func save() { self.delegate?.save() } } class QuaternaryViewController: UIViewController { weak var delegate: QuaternaryViewControllerDelegate? @IBAction func save(_ sender: UIButton) { self.delegate?.save() } } 

Using UIResponder chain extension UIResponder { func findResponder() -> T? { var responder = self.next while responder != nil { if let candidate = responder as? T { return candidate } responder = responder!.next } return nil } } 

protocol SaveProtocol: AnyObject { func save() } class PrimaryViewController : UIViewController, SaveProtocol { // snip func save() { print("Saved !!") } } // snip class QuaternaryViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() self.save() } func save() { if let saver = self.findResponder() as SaveProtocol? { saver.save() } } } Provide a Protocol 

Don’t extension UIResponder { func findResponder() -> T? { var responder = self.next while responder != nil { if let candidate = responder as? T { return candidate } responder = responder!.next } return nil } } 

Sample Code •https://gist.github.com/codelynx/ 11f1fc1dc8a0de679c05dc88016a2480 

Wrap Up • You may avoid making delegate chain by following its responder chain • Don’t abuse 

fin