---
title: "QLThumbnailDispatchAsync(_:_:_:)"
framework: quicklook
role: symbol
role_heading: Function
path: "quicklook/qlthumbnaildispatchasync(_:_:_:)"
---

# QLThumbnailDispatchAsync(_:_:_:)

Creates a thumbnail in the background on the provided background queue.

## Declaration

```swift
func QLThumbnailDispatchAsync(_ thumbnail: QLThumbnail!, _ queue: dispatch_queue_t!, _ completion: (() -> Void)!)
```

## Parameters

- `thumbnail`: The thumbnail to compute.
- `queue`: The queue that’s used to create the thumbnail.
- `completion`: The completion block that’s called when the thumbnail is created. The completion block is always called, even if the thumbnail computation is canceled.

## See Also

### Creating thumbnails

- [QLThumbnailImageCreate(_:_:_:_:)](quicklook/qlthumbnailimagecreate(_:_:_:_:).md)
- [QLThumbnailCreate(_:_:_:_:)](quicklook/qlthumbnailcreate(_:_:_:_:).md)
- [QLThumbnailCancel(_:)](quicklook/qlthumbnailcancel(_:).md)
- [QLThumbnailCopyDocumentURL(_:)](quicklook/qlthumbnailcopydocumenturl(_:).md)
- [QLThumbnailCopyImage(_:)](quicklook/qlthumbnailcopyimage(_:).md)
- [QLThumbnailCopyOptions(_:)](quicklook/qlthumbnailcopyoptions(_:).md)
- [QLThumbnailGetContentRect(_:)](quicklook/qlthumbnailgetcontentrect(_:).md)
- [QLThumbnailGetMaximumSize(_:)](quicklook/qlthumbnailgetmaximumsize(_:).md)
- [QLThumbnailGetTypeID()](quicklook/qlthumbnailgettypeid().md)
- [QLThumbnailIsCancelled(_:)](quicklook/qlthumbnailiscancelled(_:).md)