Workaround for simple protocol inheriting conformance - swift

Question

In our app, we have a service that helps us decide which Modal UIVIewController should we present next. Every ModalVIewController has common function such as dismiss() but also a specific function it implements. So that's what we tried:
The base protocol that is common to all VC's base functions.
protocol ModalScreenDelegate: AnyObject {
func modalScreenWantsToDissmiss(_ modalScreen: ModalScreen)
}
A base protocol that every UIViewController implements
protocol ModalScreen: UIViewController {
var delegate: ModalScreenDelegate? { get set }
}
Now we create a protocol with specific-implementation of ModalScreenDelegate base protocol like so:
protocol ShareToFacebookDelegate: ModalScreenDelegate {
func someCustomMethod()
}
And assign it to:
class ShareToFacebookViewController: UIViewController, ModalScreen {
weak var delegate: ModalScreenDelegate? // **WORKS**
weak var delegate: ShareToFacebookDelegate? // **DOESN'T WORKS**
}
If I'm trying to use ShareToFacebookDelegate to instead of ModalScreenDelegate the compiler throws an IDE error saying I have to change it back to ModalScreenDelegate.
Why wouldn't it work? It's ShareToFacebookDelegate conforms to ModalScreenDelegate.
Any help would be highly appreciated.
Thank you!
UPDATE Based on Alexandr Kolesnik:
Your method works. But when I try to "fetch" the correct VC within the service under one method like so:
func fetchModal<T: ModalScreen & UIViewController>() -> T? {
return AddInstagramViewController.create() as? T
}
And then have a coordinator that wants to get this vc:
guard let currentModalViewController vc = modalScreenSupplierService.fetchModal() else {
return
}
I'm getting:
Generic parameter 'T' could not be inferred
And I can't really say what T will be, all I know that it's going to conform to UIViewController & ModalScreen. Is it solvable?

Answer 1

If I understood you correctly you can use generic types to manage the problem. Look through the code below. Hope it helps
protocol ModalScreenDelegate: AnyObject {
typealias T = ModalScreenDelegate
func modalScreenWantsToDissmiss(_ modalScreen: T)
}
protocol ShareToFacebookDelegate: ModalScreenDelegate {
func someCustomMethod()
}
protocol ModalScreen: UIViewController {
associatedtype T
var delegate: T? { get set }
}
class ShareToFacebookViewController: UIViewController, ModalScreen {
typealias T = ShareToFacebookDelegate
weak var delegate: T?
override func viewDidLoad() {
super.viewDidLoad()
delegate?.someCustomMethod()
}
}
UPDATE:
class AddInstagramViewController: SuperVC {
typealias T = ShareToFacebookDelegate
private var instaDelegate: ShareToFacebookDelegate?
override var delegate: ModalScreenDelegate? {
set {
instaDelegate = newValue as? ShareToFacebookDelegate
}
get {
return instaDelegate
}
}
static func create() -> AddInstagramViewController {
return AddInstagramViewController()
}
}
class SuperVC: UIViewController, ModalScreen {
typealias T = ModalScreenDelegate
var delegate: T?
}
class Supplier {
func fetchModal<M: ModalScreen>() -> M? { return AddInstagramViewController.create() as? M }
}
class SupplierImpl {
let modalScreenSupplierService: Supplier? = nil
func goto() {
guard
let vc: SuperVC = modalScreenSupplierService?.fetchModal()
else {
return
}
}
}

Answer 2

This solution:
protocol ModalScreenDelegate: AnyObject {
func modalScreenWantsToDissmiss(_ modalScreen: ModalScreen)
}
protocol ModalScreen: UIViewController {
var delegate: (ModalScreenDelegate & ShareToFacebookDelegate)? { get set }
}
protocol ShareToFacebookDelegate: ModalScreenDelegate {
func someCustomMethod()
}
class ShareToFacebookViewController: UIViewController, ModalScreen {
weak var delegate: (ModalScreenDelegate & ShareToFacebookDelegate)?
}
or inheritance:
protocol ModalScreenDelegate: AnyObject {
func modalScreenWantsToDissmiss(_ modalScreen: ModalScreen)
}
protocol ModalScreen: ShareToFacebookDelegate where Self: UIViewController {
var delegate: ModalScreenDelegate? { get set }
}
protocol ShareToFacebookDelegate: ModalScreenDelegate {
func someCustomMethod()
}
class ShareToFacebookViewController: UIViewController, ModalScreen {
func someCustomMethod() {
}
func modalScreenWantsToDissmiss(_ modalScreen: ModalScreen) {
}
weak var delegate: ModalScreenDelegate? // **WORKS**
}