---
title: kCVReturnDisplayLinkCallbacksNotSet
framework: corevideo
role: symbol
role_heading: Global Variable
path: corevideo/kcvreturndisplaylinkcallbacksnotset
---

# kCVReturnDisplayLinkCallbacksNotSet

No callback registered for the specified display link. You must set either the output callback or both the render and display callbacks.

## Declaration

```swift
var kCVReturnDisplayLinkCallbacksNotSet: CVReturn { get }
```

## See Also

### Display Link

- [kCVReturnInvalidDisplay](corevideo/kcvreturninvaliddisplay.md)
- [kCVReturnDisplayLinkAlreadyRunning](corevideo/kcvreturndisplaylinkalreadyrunning.md)
- [kCVReturnDisplayLinkNotRunning](corevideo/kcvreturndisplaylinknotrunning.md)