PageViewController with UICollectionViewControllers

PageViewController

import UIKit

class ViewController: UIPageViewController, UIPageViewControllerDataSource {

    var collectionViewControllers: Array<UIViewController> = []
    
    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        dataSource = self   //so our delegate methods get called
        
        //use tags to reference each controller
        let collectionViewOne = TestCollectionViewController(collectionViewLayout: UICollectionViewFlowLayout())
        collectionViewOne.view.tag = 0
        let collectionViewTwo = TestCollectionViewController(collectionViewLayout: UICollectionViewFlowLayout())
        collectionViewTwo.view.tag = 1
        let collectionViewThree = TestCollectionViewController(collectionViewLayout: UICollectionViewFlowLayout())
        collectionViewThree.view.tag = 2
        
        collectionViewControllers = [collectionViewOne, collectionViewTwo, collectionViewThree]
        
        self.setViewControllers([collectionViewOne], direction: .Forward, animated: true, completion: nil)
    }
    
    
    //dataSource methods
    func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController? {
        var index = viewController.view.tag
        
        if index == 0 {
            return nil
        }
        
        if index > 0 {
            index--
        }
        return collectionViewControllers[index] as? TestCollectionViewController
    }
    
    func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
        var index = viewController.view.tag
        
        if index == 2 {
            return nil
        }
        
        if index < collectionViewControllers.count - 1 {
            index++
        }
        return collectionViewControllers[index] as? TestCollectionViewController
    }
}

TestCollectionViewController

import UIKit

class TestCollectionViewController: UICollectionViewController {

    private let reuseIdentifier = "collectionViewCell"
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        self.collectionView?.backgroundColor = UIColor.whiteColor() 
        self.collectionView?.contentInset = UIEdgeInsets(top: 50, left: 0, bottom: 0, right: 0)
        self.collectionView?.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)
    }
    
    func randomColor() -> UIColor {
        let randomInt = arc4random_uniform(4)
        var randomColor = UIColor.blackColor()
        
        switch randomInt {
        case 0:
            randomColor =  UIColor.purpleColor()
        case 1:
            randomColor = UIColor.redColor()
        case 2:
            randomColor = UIColor.greenColor()
        case 3:
            randomColor = UIColor.cyanColor()
        default:
            break
        }
        return randomColor
    }
    
}

extension TestCollectionViewController: UICollectionViewDataSource {
    
    override func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
        return 1
    }
    
    override func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 30
    }
    
    override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as! UICollectionViewCell
        cell.backgroundColor = randomColor()
        return cell
    }
}