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# AudioSessionAddPropertyListener(_:_:_:)

Adds a property listener callback function to your application’s audio session object.

```
func AudioSessionAddPropertyListener(_ inID: AudioSessionPropertyID, _ inProc: AudioSessionPropertyListener!, _ inClientData: UnsafeMutableRawPointer!) -> OSStatus
```

## Parameters

`inID`

The identifier for the audio session property whose value changes you want to listen for.

`inProc`

The name of your property listener callback function.

`inClientData`

Data that you would like to be passed to your property listener callback.

## Return Value

A result code. See Result Codes.

## Discussion

When an audio session property value changes, and you have added a listener callback for that property, the audio session object invokes the callback.

You can add exactly one listener callback for a given `inID`-`inClientData` pair. In other words, you can add more than one property listener callback function for a given audio session property, provided you pass a unique `inClientData` parameter value each time you add a property listener.

Audio session properties are listed and described in [Audio Session Property Identifiers](/documentation/AudioToolbox/1618455-audio-session-property-identifie).

---

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