---
title: AudioSessionPropertyListener
framework: audiotoolbox
role: symbol
role_heading: Type Alias
path: audiotoolbox/audiosessionpropertylistener
---

# AudioSessionPropertyListener

Invoked when an audio session property changes in iOS.

## Declaration

```swift
typealias AudioSessionPropertyListener = (UnsafeMutableRawPointer?, AudioSessionPropertyID, UInt32, UnsafeRawPointer?) -> Void
```

## Parameters

- `inClientData`: Data that you specified in the inClientData parameter of the doc://com.apple.audiotoolbox/documentation/AudioToolbox/AudioSessionAddPropertyListener(_:_:_:) function. Can be NULL.
- `inID`: The identifier for the audio session property whose value just changed. See doc://com.apple.audiotoolbox/documentation/AudioToolbox/1618455-audio-session-property-identifie.
- `inDataSize`: The size, in bytes, of the value of the changed property.
- `inData`: The new value of the changed property.

## Discussion

Discussion If you named your function MyPropertyListener, you would declare it like this: Discussion You can register one or more property listener callbacks with your application’s audio session object by calling the AudioSessionAddPropertyListener(_:_:_:) function.

## See Also

### Callbacks

- [AudioSessionInterruptionListener](audiotoolbox/audiosessioninterruptionlistener.md)