 
 extension BookController : UIPageViewControllerDelegate {
     func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
-        print("finish change page.")
+        
+        guard let index = pageViewController.viewControllers?.first?.view.tag else {
+            return
+        }
+        
+        UserDefaults.standard.set(index, forKey: UDKey.CurrentPage)
+        UserDefaults.standard.synchronize()
+        
+        self.setChapterInfo()
     }
 }
 

            return
        }
        
        settingView.preBtn.isEnabled = chapterNumber != 0
        settingView.nextBtn.isEnabled = chapterNumber != chapterInfos.count - 1
    }

            let startIndex = chapterInfo.startPage
            let endIndex = chapterInfo.endPage
            
            print("\(chapterName) : startIndex = \(startIndex), endIndex = \(endIndex)")
            
            if (currentIndex >= startIndex && currentIndex <= endIndex) {
                settingView.chapterLbl.text = chapterName
                chapterNumber = chapterInfo.chapterNumber
                
                // slideの内容を設定する.
