Delegate Chaining Workaround

Assume, you have a view controller hierarchy A, B, C and D, in some cases, you would like to access A from D. In typical strategy in iOS, you may provide numbers of delegate to navigate to A from D. I called it delegate chaining. This slide introduces you alternative way by using responder chain to access A from D.

Transcript

1. Delegate Chaining
   Workaround
   October 2010
   Kaz Yoshikawa
   

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2. About me
   

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3. Kaz Yoshikawa
   • Electricwoods LLC ୅ද / Digital Lynx Systems Inc. ෭୅ද
   • e-mail: kyoshikawa@electricwoods.com
   • 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.
   

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4. What is
   Delegate Chaining?
   

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5. 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
   

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6. 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
   

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7. 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()
   }
   }
   

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8. 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
   }
   }
   

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9. 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
   

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10. 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
    }
    }
    

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

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

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13. fin
    

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