---
title: CFRunLoopObserverCallBack
framework: corefoundation
role: symbol
role_heading: Type Alias
path: corefoundation/cfrunloopobservercallback
---

# CFRunLoopObserverCallBack

Callback invoked when a CFRunLoopObserver object is fired.

## Declaration

```swift
typealias CFRunLoopObserverCallBack = (CFRunLoopObserver?, CFRunLoopActivity, UnsafeMutableRawPointer?) -> Void
```

## Parameters

- `observer`: The run loop observer that is firing.
- `activity`: The current activity stage of the run loop.
- `info`: The info member of the doc://com.apple.corefoundation/documentation/CoreFoundation/CFRunLoopObserverContext structure that was used when creating the run loop observer.

## Discussion

Discussion You specify this callback when you create the run loop observer with CFRunLoopObserverCreate(_:_:_:_:_:_:).