I just checked it and it seems like Numbers implemented in HTML or something. I get the same long delay with a bunch of messages about networking, non-existent processes, WebProcessProxy, and WebPageProxy. Then I finally get a failure message "DID FAIL LOADING QLWeb2DisplayBundle" and the preview appears.
But my app doesn't have networking. If I enable outgoing client, then the preview appears more or less instantly. The preview still isn't correct. Instead of being a large icon, it's the upper left portion of the content.
QLThumbnailGenerator sounds like an interesting idea.
Topic:
UI Frameworks
SubTopic:
AppKit
Tags: