#817 (three column layout)

- Scrolling story instead of pages.
- Change pages vertically only when at the top or bottom of a story.

clients/ios/Classes/DetailObjCViewController.m

@@ -1278,6 +1278,8 @@
         [appDelegate.feedDetailViewController redrawUnreadStory];
 //    }
     
+    [appDelegate.detailViewController allowPagingUp:YES down:NO];
+    
     if (!appDelegate.storiesCollection.inSearch) {
         [self.currentStoryController becomeFirstResponder];
     }

clients/ios/Classes/DetailViewController.swift

@@ -128,6 +128,14 @@ class DetailViewController: DetailObjCViewController {
     /// The horizontal page view controller.
     var horizontalPageViewController: HorizontalPageViewController?
     
+    /// Enable paging upwards and/or downwards.
+    ///
+    /// - Parameter up: Allow paging up to the previous story.
+    /// - Parameter down: Allow paging down to the next story.
+    @objc(allowPagingUp:down:) func allowPaging(up: Bool, down: Bool) {
+        horizontalPageViewController?.currentController?.allowPaging(up: up, down: down)
+    }
+    
     /// Returns the currently displayed story view controller, or `nil` if none.
     @objc var currentStoryController: StoryDetailViewController? {
         return horizontalPageViewController?.currentController?.currentController

clients/ios/Classes/StoryDetailObjCViewController.m

@@ -1456,6 +1456,8 @@
         }
         
         [self storeScrollPosition:YES];
+        
+        [appDelegate.detailViewController allowPagingUp:atTop down:atBottom];
     }
 }
 

clients/ios/Classes/VerticalPageViewController.swift

@@ -45,6 +45,33 @@ class VerticalPageViewController: UIPageViewController {
     /// The next story view controller, if it has been requested, otherwise `nil`.
     var nextController: StoryDetailViewController?
     
+    /// The internal scroll view that drives the page controller.
+    var scrollView: UIScrollView? {
+        return view.subviews.filter { $0 is UIScrollView }.first as? UIScrollView
+    }
+    
+    private var isPageUpEnabled = true
+    private var isPageDownEnabled = true
+    
+    override func viewDidLoad() {
+        super.viewDidLoad()
+        
+        self.scrollView?.delegate = self
+    }
+    
+    /// Updates whether paging up and/or down is enabled.
+    func allowPaging(up: Bool, down: Bool) {
+        isPageUpEnabled = up
+        isPageDownEnabled = down
+        
+        if !isPageUpEnabled {
+            print("Page Up Disabled")
+        }
+        if !isPageDownEnabled {
+            print("Page Down Disabled")
+        }
+    }
+    
     /// Clear the previous and next story view controllers.
     func reset() {
         previousController = nil
@@ -67,3 +94,32 @@ class VerticalPageViewController: UIPageViewController {
         super.setViewControllers(viewControllers, direction: direction, animated: animated, completion: completion)
     }
 }
+
+extension VerticalPageViewController: UIScrollViewDelegate {
+    func scrollViewDidScroll(_ scrollView: UIScrollView) {
+        print("contentOffset = \(scrollView.contentOffset.y)")
+        
+        if !self.isPageUpEnabled {
+            disableUpScroll(scrollView)
+        }
+        if !self.isPageDownEnabled {
+            disableDownScroll(scrollView)
+        }
+    }
+    
+    private func disableUpScroll(_ scrollView: UIScrollView) {
+        let viewHeight = view.bounds.height
+        
+        if scrollView.contentOffset.y < viewHeight {
+            scrollView.setContentOffset(CGPoint(x: 0, y: viewHeight), animated: false)
+        }
+    }
+    
+    private func disableDownScroll(_ scrollView: UIScrollView) {
+        let viewHeight = view.bounds.height
+        
+        if scrollView.contentOffset.y > viewHeight {
+            scrollView.setContentOffset(CGPoint(x: 0, y: viewHeight), animated: false)
+        }
+    }
+}