Custom segue class that launches a new storyboard.

APLaunchNewStoryboardSegue.swift

//
//  APLaunchNewStoryboardSegue.swift
//  APLaunchNewStoryboardSegue gist
//
//  Created by Warren Gavin on 30/11/15.
//  Copyright © 2015 Apokrupto. All rights reserved.
//

import UIKit

/**
 *    Custom segue class that launches a new storyboard. This will appear in the storyboard's segue list
 *    when creating a new segue as "launch new storyboard"
 *
 *    To use the segue in a storyboad:
 *       o Select it as the custom segue when linking two view controllers
 *       o The destination view controller should be a simple blank VC, it is a place holder.
 *       o Name the segue identifier <storyboard>[.<scene>]
 *          - i.e If you want to launch the storyboard "Foo.storyboard" name the
 *            segue "Foo". If you want to launch a specific scene "bar" in the
 *            storyboard "Foo.storyboard" name the segue "Foo.bar"
 *       o All storyboards MUST have an initial view controller, if they don't
 *         the placeholder destination view controller will be presented
 *
 */
@objc(APLaunchNewStoryboardSegue)  // See http://stackoverflow.com/questions/24185345/custom-segue-in-swift why this is necessary
class APLaunchNewStoryboardSegue: UIStoryboardSegue {
    
    override init(identifier: String?, source: UIViewController, destination: UIViewController) {
        var realDestination = APLaunchNewStoryboardSegue.controllerForNewSceneInStoryboard(identifier)
        
        if nil == realDestination {
            realDestination = destination
        }
        
        super.init(identifier: identifier, source: source, destination: realDestination!)
    }
    
    override func perform() {
        let source = self.sourceViewController
        
        if source.respondsToSelector("showViewController:sender:") {
            source.showViewController(self.destinationViewController, sender: source)
        }
        else if let naviationController = source.navigationController {
            naviationController.pushViewController(self.destinationViewController, animated: true)
        }
        else {
            source.presentViewController(self.destinationViewController, animated: true, completion: nil)
        }
    }

}


private extension APLaunchNewStoryboardSegue {
    
    /**
     *    Create a view controller for a particular scene in a particular storyboard
     *
     *    @param sceneNameWithStoryboard Defined as "storyboard_name" or "storyboard_name.scene_name"
     *                                   for a specific scene in the storyboard.
     *                                   If no scene name is given the initial view controller for
     *                                   the storyboard is returned.
     *
     *    @return view controller for a storyboard scene
     */
    private static func controllerForNewSceneInStoryboard(sceneNameWithStoryBoard: String?) -> UIViewController? {
        guard let sceneNameWithStoryBoard = sceneNameWithStoryBoard where sceneNameWithStoryBoard.characters.count > 0 else {
            return nil
        }
        
        // Segue components are [storyboard, sceneName] or [storyboard]
        let segueComponents = sceneNameWithStoryBoard.componentsSeparatedByString(".")
        let storyboard = UIStoryboard(name: segueComponents[0], bundle: nil)
        
        // If no scene specified, return the initial view controller
        if 1 == segueComponents.count {
            return storyboard.instantiateInitialViewController()
        }
        
        return storyboard.instantiateViewControllerWithIdentifier(segueComponents[1])
    }
    
}