# previewController(_:transitionImageFor:contentRect:) Tells the delegate that the system is about to present the preview full screen or dismiss it, and asks for information to provide a smooth transition when zooming. ``` optional func previewController(_ controller: QLPreviewController, transitionImageFor item: any QLPreviewItem, contentRect: UnsafeMutablePointer) -> UIImage? ``` ## Parameters `controller` The [`QLPreviewController`](/documentation/QuickLook/QLPreviewController) that’s requesting the image for the preview item. `item` The item to preview or dismiss. `contentRect` The rectangle within the image that represents the document content. For icons, for example, the document content rectangle is typically smaller than the icon rectangle itself. ## Return Value A object that the preview controller cross-fades with when zooming. ## Discussion> Note: > Starting with macOS 11, animated transitions are available for Mac apps built with Mac Catalyst. On Mac computers running a version earlier than macOS 11, the system doesn’t call this delegate method. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)