【Swift】PageViewControllerでスクロールできない

Question

赤い画面からスクロールできません。
ここを参照しました

import UIKit

class PageViewController: UIPageViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        self.setViewControllers([getFirst()], direction: .Forward, animated: true, completion: nil)
        // Do any additional setup after loading the view.
    }
    
    func getFirst() -> ChatViewController {
        return storyboard!.instantiateViewControllerWithIdentifier("ChatViewController") as! ChatViewController
    }
    
    func getSecond() -> RankingViewController {
        return storyboard!.instantiateViewControllerWithIdentifier("RankingViewController") as! RankingViewController
    }
    
    func getThird() -> ReviewViewController {
        return storyboard!.instantiateViewControllerWithIdentifier("ReviewViewController") as! ReviewViewController
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    

    /*
    // MARK: - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        // Get the new view controller using segue.destinationViewController.
        // Pass the selected object to the new view controller.
    }
    */

}

//以下追加
extension PageViewController : UIPageViewControllerDataSource {
    
    func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController? {
        if viewController.isKindOfClass(ReviewViewController) {
            // レビュー -> ランキング
            return getSecond()
        } else if viewController.isKindOfClass(RankingViewController) {
            // ランキング -> チャット
            return getFirst()
        } else {
            // チャット -> end of the road
            return nil
        }
    }
    
    func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
        if viewController.isKindOfClass(ChatViewController) {
            // チャット -> ランキング
            return getSecond()
        } else if viewController.isKindOfClass(RankingViewController) {
            // 2 -> 3
            return getThird()
        } else {
            // レビュー -> end of the road
            return nil
        }
    }
}

Answer 1

viewDidLoadの中に重要な1行が抜けてますね、、、

self.dataSource = self