#Short brief Currently, I have a complex project that have 5 storyboards, with 20 controllers. In my case, using storyboard segue seems not a good idea. Therefore, creating controller's instance from storyboard and make a transition by code is much better.

But the problem is that instantiateViewController(withIdentifier:) always return non-optional instance, and it will be crashed if we put an invalid identifier (which didn't define in storyboard).

#Solution (Swift 3.0) There are steps to prevent this problem.

1. In *.storyboard, use controller class name as StoryboardID
2. Create UIStoryboard+Ext.swift to define all storyboards & controllers belong
3. Create BaseViewController.swift to define the initialization from storyboard
4. Create function to init all storyboards & controllers, to prevent crashing in runtime.

#Detail (TL;DR)

Step 1:

Step 2:

extension UIStoryboard {
    
    enum Identifier: String {
        case main = "Main"
        case explore = "Explore"
        case search = "Search"
        case profile = "Profile"
    }
    
    static func name(for controller: UIViewController.Type) -> String? {
        var identifier: Identifier?
        switch controller.className {
        case HomeViewController.className:
            identifier = .main
        case ExploreViewController.className:
            identifier = .explore
        case SearchViewController.className:
            identifier = .search
        case ProfileViewController.className:
            identifier = .profile
        default:
            break
        }
        return identifier?.rawValue
    }
}

extension UIStoryboard {

    static func instanceFromIdentifier(_ identifier: Identifier) -> UIStoryboard {
        return UIStoryboard(name: identifier.rawValue, bundle: Bundle.main)
    }
    
    static func instanceFromName(_ name: String) -> UIStoryboard? {
        guard let identifier = Identifier(rawValue: name) else { return nil }
        return instanceFromIdentifier(identifier)
    }
    
}

Step 3:

extension UIViewController {
    
    var className: String {
        return String(describing: type(of: self))
    }
    
    class var className: String {
        return String(describing: self)
    }
    
}

class BaseViewController: UIViewController {
    
    static var controllerId: String {
        return String(describing: self) // return slass name, i.e "ExploreViewController"
    }
    
    static func instanceFromStoryboard() -> Self? {
        guard let storyboardName = UIStoryboard.name(for: self) else { return nil }
        return instantiateFrom(storyboardName: storyboardName)
    }
    
    private static func instantiateFrom<VC: UIViewController>(storyboardName: String) -> VC? {
        let storyboard = UIStoryboard(name: storyboardName, bundle: nil)
        let controller = storyboard.instantiateViewController(withIdentifier: controllerId) as? VC
        return controller
    }
}

Step 4

extension AppDelegate {
    func validateStoryboards() {
        guard
            let _ = UIStoryboard.instanceFromName(UIStoryboard.Identifier.main.rawValue),
            let _ = UIStoryboard.instanceFromName(UIStoryboard.Identifier.explore.rawValue),
            let _ = UIStoryboard.instanceFromName(UIStoryboard.Identifier.profile.rawValue),
            let _ = UIStoryboard.instanceFromName(UIStoryboard.Identifier.search.rawValue)
            else {
                fatalError("fail to init storyboard by name")
        }
        
        guard let _ = HomeViewController.instanceFromStoryboard(),
            let _ = ExploreViewController.instanceFromStoryboard(),
            let _ = ProfileViewController.instanceFromStoryboard(),
            let _ = SearchViewController.instanceFromStoryboard()
            else {
                fatalError("fail to init controller from storyboard")
        }
    }
}