Question asked during the 6-6-23 UIKit Q&A Slack session of WWDC 2023
My iOS / iPadOS / Catalyst app has a thumbnail extension with a QLThumbnailProvider subclass that implements the provideThumbnail(for:_:) method providing the thumbnail for a document created in my app, by drawing the thumbnail image into the current context. That implementation successfully updates the thumbnail for the document, but sometimes the thumbnail's displayed image (in, for instance, the Files app or my app's own UIDocumentBrowserViewController on iPhone or iPad) is slow to update. (This update slowness seems especially to be a problem for documents stored in iCloud Drive, rather than in local storage.)
(1) Am I correct in presuming that the displayed thumbnail images are cached somewhere, and the reason the displayed thumbnail images are slow to update is because either (a) the thumbnail cache is slow to update and/or (b) the system only periodically calls the provideThumbnail(for:_:) method?
(2) If so, is there some way my app can either (a) force the thumbnail image cache to update more quickly and/or (b) force the provideThumbnail(for:_:) method to be called, so that the displayed thumbnail images for the created/modified documents are quicker to update?
