From b284aa8a079df15777584285daf09ec3c0f8a266 Mon Sep 17 00:00:00 2001
From: Doug <6060466+pixlwave@users.noreply.github.com>
Date: Fri, 7 Feb 2025 10:48:09 +0000
Subject: [PATCH] Fix a bug where the preview controller breaks when swiping
 quickly. (#3750)

---
 .../View/TimelineMediaPreviewController.swift | 21 +++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/ElementX/Sources/Screens/FilePreviewScreen/View/TimelineMediaPreviewController.swift b/ElementX/Sources/Screens/FilePreviewScreen/View/TimelineMediaPreviewController.swift
index 2c3f560f6..b52a32cf8 100644
--- a/ElementX/Sources/Screens/FilePreviewScreen/View/TimelineMediaPreviewController.swift
+++ b/ElementX/Sources/Screens/FilePreviewScreen/View/TimelineMediaPreviewController.swift
@@ -25,6 +25,7 @@ class TimelineMediaPreviewController: QLPreviewController {
     
     private var navigationBar: UINavigationBar? { view.subviews.first?.subviews.first { $0 is UINavigationBar } as? UINavigationBar }
     private var toolbar: UIToolbar? { view.subviews.first?.subviews.last { $0 is UIToolbar } as? UIToolbar }
+    private var pageScrollView: UIScrollView? { view.firstScrollView() }
     private var captionView: UIView { captionHostingController.view }
     
     override var overrideUserInterfaceStyle: UIUserInterfaceStyle {
@@ -184,6 +185,13 @@ class TimelineMediaPreviewController: QLPreviewController {
     
     private func handleFileLoaded(itemID: TimelineItemIdentifier.EventOrTransactionID) {
         guard (currentPreviewItem as? TimelineMediaPreviewItem.Media)?.id == itemID else { return }
+        
+        // There's a bug where refreshCurrentPreviewItem completely breaks the QLPreviewController
+        // if it's called whilst swiping between items. So don't let that happen.
+        if let scrollView = pageScrollView, scrollView.isDragging || scrollView.isDecelerating {
+            return
+        }
+        
         refreshCurrentPreviewItem()
     }
     
@@ -336,6 +344,19 @@ private struct DownloadIndicatorView: View {
     }
 }
 
+// MARK: - Helpers
+
+private extension UIView {
+    func firstScrollView() -> UIScrollView? {
+        for view in subviews {
+            if let scrollView = view as? UIScrollView ?? view.firstScrollView() {
+                return scrollView
+            }
+        }
+        return nil
+    }
+}
+
 private extension UISheetPresentationController.Detent {
     static func height(_ height: CGFloat) -> UISheetPresentationController.Detent {
         .custom { _ in height }