---
title: VNRequestCompletionHandler
framework: vision
role: symbol
role_heading: Type Alias
path: vision/vnrequestcompletionhandler
---

# VNRequestCompletionHandler

A type alias to encapsulate the syntax for the completion handler the system calls after the request finishes processing.

## Declaration

```swift
typealias VNRequestCompletionHandler = (VNRequest, (any Error)?) -> Void
```

## Discussion

Discussion Vision executes the completion handler on the same queue that it executes the request; however, this queue differs from the one where you called perform(_:).

## See Also

### Configuring a Request

- [completionHandler](vision/vnrequest/completionhandler.md)
- [preferBackgroundProcessing](vision/vnrequest/preferbackgroundprocessing.md)
- [results](vision/vnrequest/results.md)
- [revision](vision/vnrequest/revision.md)
- [usesCPUOnly](vision/vnrequest/usescpuonly.md)