Merge pull request #3687 from wikimedia/fix_on_this_day_header

joewalsh · web-flow · commit dfe6905c792e · 2020-09-14T16:33:44.000-04:00
Fix on this day header - merge into main
diff --git a/Wikipedia/Code/NavigationBarHider.swift b/Wikipedia/Code/NavigationBarHider.swift
@@ -32,23 +32,49 @@ public class NavigationBarHider: NSObject {
     
     fileprivate var isUserScrolling: Bool = false
     fileprivate var isScrollingToTop: Bool = false
+    fileprivate var isProgramaticallyScrolling: Bool = false
     var initialScrollY: CGFloat = 0
     var initialNavigationBarPercentHidden: CGFloat = 0
+
+    private func setDataForScroll(yOffset: CGFloat, topContentInset: CGFloat) {
+        guard let navigationBar = navigationBar else {
+            return
+        }
+        initialScrollY = yOffset + topContentInset
+        initialNavigationBarPercentHidden = navigationBar.navigationBarPercentHidden
+    }
+
+    public func setIsProgramaticallyScrolling(_ isProgramaticallyScrolling: Bool, yOffset: CGFloat, topContentInset: CGFloat) {
+        guard navigationBar?.isInteractiveHidingEnabled == true else {
+            return
+        }
+        
+        self.isProgramaticallyScrolling = isProgramaticallyScrolling
+
+        if isProgramaticallyScrolling {
+            setDataForScroll(yOffset: yOffset, topContentInset: topContentInset)
+        }
+    }
     
     @objc public func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
-        guard let navigationBar = navigationBar, navigationBar.isInteractiveHidingEnabled else {
+        guard navigationBar?.isInteractiveHidingEnabled == true else {
             return
         }
         isUserScrolling = true
-        initialScrollY = scrollView.contentOffset.y + scrollView.contentInset.top
-        initialNavigationBarPercentHidden = navigationBar.navigationBarPercentHidden
+        setDataForScroll(yOffset: scrollView.contentOffset.y, topContentInset: scrollView.contentInset.top)
     }
 
     @objc public func scrollViewDidScroll(_ scrollView: UIScrollView) {
         guard let navigationBar = navigationBar else {
             return
         }
-        
+
+        if isProgramaticallyScrolling {
+            /// When programatically scrolling on a just-created scroll view, we need a layout pass to get accurate heights.
+            scrollView.layoutIfNeeded()
+            navigationBar.layoutIfNeeded()
+        }
+
         guard scrollView.contentSize.height > 0 else {
             if navigationBar.isAdjustingHidingFromContentInsetChangesEnabled  {
                 navigationBar.setNavigationBarPercentHidden(0, underBarViewPercentHidden: 0, extendedViewPercentHidden: 0, topSpacingPercentHidden: 0, animated: false)
@@ -78,7 +104,7 @@ public class NavigationBarHider: NSObject {
             }
         }
 
-        guard navigationBar.isInteractiveHidingEnabled, isUserScrolling || isScrollingToTop || scrollY < totalHideableHeight else {
+        guard navigationBar.isInteractiveHidingEnabled, isUserScrolling || isScrollingToTop || isProgramaticallyScrolling || scrollY < totalHideableHeight else {
             return
         }
         
@@ -234,8 +260,7 @@ public class NavigationBarHider: NSObject {
         guard let navigationBar = navigationBar, navigationBar.isInteractiveHidingEnabled else {
             return
         }
-        initialNavigationBarPercentHidden = navigationBar.navigationBarPercentHidden
-        initialScrollY = scrollView.contentOffset.y + scrollView.contentInset.top
+        setDataForScroll(yOffset: scrollView.contentOffset.y, topContentInset: scrollView.contentInset.top)
         isScrollingToTop = true
     }
 
diff --git a/Wikipedia/Code/OnThisDayViewController.swift b/Wikipedia/Code/OnThisDayViewController.swift
@@ -96,7 +96,9 @@ class OnThisDayViewController: ColumnarCollectionViewController, DetailPresentin
             return
         }
         let sectionIndex = eventIndex + 1 // index + 1 because section 0 is the header
+        isProgramaticallyScrolling = true
         collectionView.scrollToItem(at: IndexPath(item: 0, section: sectionIndex), at: sectionIndex < 1 ? .top : .centeredVertically, animated: false)
+        isProgramaticallyScrolling = false
     }
     
     override func scrollViewInsetsDidChange() {
@@ -147,6 +149,12 @@ class OnThisDayViewController: ColumnarCollectionViewController, DetailPresentin
     // MARK: - ColumnarCollectionViewLayoutDelegate
     
     override func collectionView(_ collectionView: UICollectionView, estimatedHeightForHeaderInSection section: Int, forColumnWidth columnWidth: CGFloat) -> ColumnarCollectionViewLayoutHeightEstimate {
+
+        /// When presenting with navigation bar, first two section headers do not exist.
+        guard !shouldShowNavigationBar || section >= 2 else {
+            return ColumnarCollectionViewLayoutHeightEstimate(precalculated: false, height: 0)
+        }
+
         guard section > 0 else {
             return super.collectionView(collectionView, estimatedHeightForHeaderInSection: section, forColumnWidth: columnWidth)
         }
diff --git a/Wikipedia/Code/ViewController.swift b/Wikipedia/Code/ViewController.swift
@@ -29,6 +29,15 @@ class ViewController: PreviewingViewController, NavigationBarHiderDelegate {
         return NavigationBarHider()
     }()
 
+    var isProgramaticallyScrolling: Bool = false {
+        didSet {
+            guard let yOffset = scrollView?.contentOffset.y, let topInset = scrollView?.contentInset.top else {
+                return
+            }
+            navigationBarHider.setIsProgramaticallyScrolling(isProgramaticallyScrolling, yOffset: yOffset, topContentInset: topInset)
+        }
+    }
+
     private var keyboardFrame: CGRect? {
         didSet {
             keyboardDidChangeFrame(from: oldValue, newKeyboardFrame: keyboardFrame)
