Workaround for UIViewController containment bug

ViewController.swift

//
//  ViewController.swift
//  ContainerTimingBugDemo
//
//  Created by Jason Pepas on 11/12/15.
//  Copyright © 2015 Jason Pepas. All rights reserved.
//

/*

Instructions:

1. Create a new "Single View Application" Xcode project.
2. Replace the contents of ViewController.swift with this gist.
3. Uncomment the below test cases one-by-one.

*/

import UIKit

class ViewController: UIViewController
{
    override func viewDidAppear(animated: Bool)
    {
        super.viewDidAppear(animated)
        
//        self.presentViewController(VCTestCase1(), animated: true, completion: nil)
//        self.presentViewController(VCTestCase2(), animated: true, completion: nil)
//        self.presentViewController(VCTestCase3(), animated: true, completion: nil)
        self.presentViewController(VCTestCase4(), animated: true, completion: nil)
//        self.presentViewController(VCTestCase5(), animated: true, completion: nil)
//        self.presentViewController(VCTestCase6(), animated: true, completion: nil)
    }
}

extension UIViewController
{
    func ensureViewHasLoaded()
    {
        let _ = view
    }
}

extension UIViewController
{
    func containChildViewController(childVC:UIViewController, inView containerView:UIView)
    {
        addChildViewController(childVC)
        
        if shouldAutomaticallyForwardAppearanceMethods()
        {
            containerView.addSubview(childVC.view)
        }
        else
        {
            childVC.ensureViewHasLoaded()
            childVC.beginAppearanceTransition(true, animated: false)
            containerView.addSubview(childVC.view)
            childVC.endAppearanceTransition()
        }
        
        childVC.didMoveToParentViewController(self)
        containerView.bringSubviewToFront(childVC.view)
        
        childVC.view.translatesAutoresizingMaskIntoConstraints = false
    }
    
    func containChildViewController(child:UIViewController)
    {
        self.containChildViewController(child, inView:view)
    }
}

class VerboseVC: UIViewController
{
    override func viewDidLoad()
    {
        debugPrint("\(self.dynamicType): \(__FUNCTION__)")
        super.viewDidLoad()
    }
    
    override func viewWillAppear(animated: Bool)
    {
        debugPrint("\(self.dynamicType): \(__FUNCTION__)")
        super.viewWillAppear(animated)
    }
    
    override func viewDidAppear(animated: Bool)
    {
        debugPrint("\(self.dynamicType): \(__FUNCTION__)")
        super.viewDidAppear(animated)
    }
    
    override func viewWillDisappear(animated: Bool)
    {
        debugPrint("\(self.dynamicType): \(__FUNCTION__)")
        super.viewWillDisappear(animated)
    }
    
    override func viewDidDisappear(animated: Bool)
    {
        debugPrint("\(self.dynamicType): \(__FUNCTION__)")
        super.viewDidDisappear(animated)
    }
}

class ChildVC: VerboseVC {}

class ViewLifeCycleTracker
{
    enum State
    {
        case OffScreen
        case TransitioningOnScreen
        case OnScreen
        case TransitioningOffScreen
    }
    
    var state: State = .OffScreen
    
    func viewWillAppear()
    {
        state = .TransitioningOnScreen
    }
    
    func viewDidAppear()
    {
        state = .OnScreen
    }
    
    func viewWillDisappear()
    {
        state = .TransitioningOffScreen
    }
    
    func viewDidDisappear()
    {
        state = .OffScreen
    }
}

class ViewControllerWithContainerLifeCycleBugWorkaround: UIViewController
{
    let tracker = ViewLifeCycleTracker()
    
    override func shouldAutomaticallyForwardAppearanceMethods() -> Bool
    {
        return !(tracker.state == .TransitioningOnScreen)
    }
    
    override func viewWillAppear(animated: Bool)
    {
        tracker.viewWillAppear()
        super.viewWillAppear(animated)
    }
    
    override func viewDidAppear(animated: Bool)
    {
        tracker.viewDidAppear()
        super.viewDidAppear(animated)
    }
    
    override func viewWillDisappear(animated: Bool)
    {
        tracker.viewWillDisappear()
        super.viewWillDisappear(animated)
    }
    
    override func viewDidDisappear(animated: Bool)
    {
        tracker.viewDidDisappear()
        super.viewDidDisappear(animated)
    }
}

class VCTestCase: ViewControllerWithContainerLifeCycleBugWorkaround {}

class VerboseVCTestCase: VCTestCase
{
    override func viewDidLoad()
    {
        debugPrint("\(self.dynamicType): \(__FUNCTION__)")
        super.viewDidLoad()
    }
    
    override func viewWillAppear(animated: Bool)
    {
        debugPrint("\(self.dynamicType): \(__FUNCTION__)")
        super.viewWillAppear(animated)
    }
    
    override func viewDidAppear(animated: Bool)
    {
        debugPrint("\(self.dynamicType): \(__FUNCTION__)")
        super.viewDidAppear(animated)
    }
    
    override func viewWillDisappear(animated: Bool)
    {
        debugPrint("\(self.dynamicType): \(__FUNCTION__)")
        super.viewWillDisappear(animated)
    }
    
    override func viewDidDisappear(animated: Bool)
    {
        debugPrint("\(self.dynamicType): \(__FUNCTION__)")
        super.viewDidDisappear(animated)
    }
}

class VCTestCase1: VerboseVCTestCase
{
    override func viewDidLoad()
    {
        super.viewDidLoad()
        
        // CORRECT: SubViewController will correctly receive viewWillAppear and viewDidAppear
        containChildViewController(ChildVC())
    }
}

class VCTestCase2: VerboseVCTestCase
{
    override func viewWillAppear(animated: Bool)
    {
        // CORRECT: SubViewController will correctly receive viewWillAppear and viewDidAppear
        self.containChildViewController(ChildVC())
        
        super.viewWillAppear(animated)
    }
}

class VCTestCase3: VerboseVCTestCase
{
    override func viewWillAppear(animated: Bool)
    {
        super.viewWillAppear(animated)
        
        // CORRECT: SubViewController will correctly receive viewWillAppear and viewDidAppear
        self.containChildViewController(ChildVC())
    }
}

class VCTestCase4: VerboseVCTestCase
{
    override func viewWillAppear(animated: Bool)
    {
        super.viewWillAppear(animated)
        
        dispatch_async(dispatch_get_main_queue()) { () -> Void in
            // CORRECT: SubViewController will correctly receive viewWillAppear and viewDidAppear
            // This is the case which is fixed by ViewControllerWithContainerLifeCycleBugWorkaround
            self.containChildViewController(ChildVC())
        }
    }
}

class VCTestCase5: VerboseVCTestCase
{
    override func viewDidAppear(animated: Bool)
    {
        // CORRECT: SubViewController will correctly receive viewWillAppear and viewDidAppear
        self.containChildViewController(ChildVC())
        
        super.viewDidAppear(animated)
    }
}

class VCTestCase6: VerboseVCTestCase
{
    override func viewDidAppear(animated: Bool)
    {
        super.viewDidAppear(animated)
        
        // CORRECT: SubViewController will correctly receive viewWillAppear and viewDidAppear
        self.containChildViewController(ChildVC())
    }
}