# QLThumbnailRequestSetImageWithData(_:_:_:) Sets the response to the thumbnail request to image data saved within the document. ``` func QLThumbnailRequestSetImageWithData(_ thumbnail: QLThumbnailRequest!, _ data: CFData!, _ properties: CFDictionary!) ``` ## Parameters `thumbnail` The thumbnail request object. `data` The image data, which must be in a format supported by the Image I/O framework (JPG, PNG, and so on). In other words, a content type of `kUTTypeImage` is assumed. (`ImageIO.framework` is a subframework of the umbrella Application Services framework.) `properties` A dictionary of properties. The only property that you can currently specify is kCGImageSourceTypeIdentifierHint; see [Quartz 2D Programming Guide](https://developer.apple.com/library/archive/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/Introduction/Introduction.html#//apple_ref/doc/uid/TP30001066) for information about this property. ## Discussion This function returns the thumbnail as a `CFData` object containing image data. The document’s application must save this data as part of the document’s data; the generator retrieves it and uses this function to return it to the client. Before you call this function, call [`QLThumbnailRequestGetMaximumSize(_:)`](/documentation/QuickLook/QLThumbnailRequestGetMaximumSize(_:)) to obtain the maximum allowed size for the thumbnail and resize the image if necessary. ### Special Considerations Thread-safety: This function should be called in the same thread as the thumbnail request is made in; generally, this is the same thread in which the `GenerateThumbnailForURL` callback was invoked. --- 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)