Open Radar

 
Area:
Something not on this list

Summary:
When pressing the list item in the navigation bar of a QLPreviewController with many items (e.g. >= 50), the main thread is blocked while the list is configured and shown. When opening the list with less than 50 items, it'll appear within around 10 seconds on an iPad Air 2 Simulator.
This only happens on iPads and when the width trait is regular size (so that the list is presented in a popover).

Steps to Reproduce:
1. Create a project with a QLPreviewController whose dataSource returns more than 50 items.
2. Present the QLPreviewController on an iPad.
3. Click the list button.

OR

1. Open and run the attached sample project on an iPad.
2. [Optional] Configure number of items.
3. Click "Show QLPreviewController" Button.
4. Click the list button.

Expected Results:
The list shows more or less immediately while the previews for the items in the list are loaded asynchronously.

Actual Results:
The main thread is blocked until the list appears.

Version:
iOS 10.1 (14B72)

Notes:
On all other configurations (when the list is presented fullscreen) it works as expected.

Configuration:
Any iPad or iPad Simulator. App needs to have regular width.

Attachments:
'QLPreviewTester.zip' was successfully uploaded.