This property is only valid if the Category is set to PlayAndRecord.
If this property is set to Speaker when a headset is plugged, this will also switch the input to use the system microphone, and not the one on the headset.
The setting of this variable is reset when a headset are plugged or unplugged.
If there is an error reading or setting the property, this will raise an MonoMac.AudioToolbox.AudioSessionException.