How to override trait collection for initial UIViewController? (with Storyboard)

I understand that you wanted a SWIFT translation here... And you've probably solved that.

Below is something I've spent a considerable time trying to resolve - getting my SplitView to work on an iPhone 6+ - this is a Cocoa solution.

My Application is TabBar based and the SplitView has Navigation Controllers. In the end my issue was that setOverrideTraitCollection was not being sent to the correct target.

@interface myUITabBarController ()

@property (nonatomic, retain) UITraitCollection *overrideTraitCollection;

@end

@implementation myUITabBarController

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self performTraitCollectionOverrideForSize:self.view.bounds.size];
}

- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator
{
    NSLog(@"myUITabBarController %@", NSStringFromSelector(_cmd));
    [self performTraitCollectionOverrideForSize:size];

    [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
}

- (void)performTraitCollectionOverrideForSize:(CGSize)size
{
    NSLog(@"myUITabBarController %@", NSStringFromSelector(_cmd));

    _overrideTraitCollection = nil;

    if (size.width > 320.0)
    {
        _overrideTraitCollection = [UITraitCollection traitCollectionWithHorizontalSizeClass:UIUserInterfaceSizeClassRegular];
    }

    [self setOverrideTraitCollection:_overrideTraitCollection forChildViewController:self];

    for (UIViewController * view in self.childViewControllers)
    {
        [self setOverrideTraitCollection:_overrideTraitCollection forChildViewController:view];
        NSLog(@"myUITabBarController %@ AFTER  viewTrait=%@", NSStringFromSelector(_cmd), [view traitCollection]);
    }
}

@end

Ok, I wish there was another way around this, but for now I just converted code from the Apple example to Swift and adjusted it to use with Storyboards.

It works, but I still believe it is an awful way to archive this goal.

My TraitOverride.swift:

import UIKit

class TraitOverride: UIViewController {

    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    var forcedTraitCollection: UITraitCollection? {
        didSet {
            updateForcedTraitCollection()
        }
    }

    override func viewDidLoad() {
        setForcedTraitForSize(view.bounds.size)
    }

    var viewController: UIViewController? {
        willSet {
            if let previousVC = viewController {
                if newValue !== previousVC {
                    previousVC.willMoveToParentViewController(nil)
                    setOverrideTraitCollection(nil, forChildViewController: previousVC)
                    previousVC.view.removeFromSuperview()
                    previousVC.removeFromParentViewController()
                }
            }
        }

        didSet {
            if let vc = viewController {
                addChildViewController(vc)
                view.addSubview(vc.view)
                vc.didMoveToParentViewController(self)
                updateForcedTraitCollection()
            }
        }
    }

    override func viewWillTransitionToSize(size: CGSize, withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator!) {
        setForcedTraitForSize(size)
        super.viewWillTransitionToSize(size, withTransitionCoordinator: coordinator)
    }

    func setForcedTraitForSize (size: CGSize) {

        let device = traitCollection.userInterfaceIdiom
        var portrait: Bool {
            if device == .Phone {
                return size.width > 320
            } else {
                return size.width > 768
            }
        }

        switch (device, portrait) {
        case (.Phone, true):
            forcedTraitCollection = UITraitCollection(horizontalSizeClass: .Regular)
        case (.Pad, false):
            forcedTraitCollection = UITraitCollection(horizontalSizeClass: .Compact)
        default:
            forcedTraitCollection = nil
        }
    }

    func updateForcedTraitCollection() {
        if let vc = viewController {
            setOverrideTraitCollection(self.forcedTraitCollection, forChildViewController: vc)
        }
    }

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        performSegueWithIdentifier("toSplitVC", sender: self)
    }

    override func prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) {
        if segue.identifier == "toSplitVC" {
            let destinationVC = segue.destinationViewController as UIViewController
            viewController = destinationVC
        }
    }

    override func shouldAutomaticallyForwardAppearanceMethods() -> Bool {
        return true
    }

    override func shouldAutomaticallyForwardRotationMethods() -> Bool {
        return true
    }
}

To make it work you need to add a new UIViewController on the storyboard and made it the initial. Add show segue from it to your real controller like this:

You need to name the segue "toSplitVC":

and set initial controller to be TraitOverride:

Now it should work for you too. Let me know if you find a better way or any flaws in this one.