Retrieving and setting the volume
Retrieving the volume is as simple as calling the getVolume() function:
Similarly to set the volume:
Listening for change events
Listening to volume change events is achieved by calling
register specifying the stream of interest.
Volume events are dispatched when either the user changes the volume using the native controls, or by
pressing the volume buttons, or when you change the volume using the setVolume function.
You should make sure you call
unregister when you are done listening to cleanup and remove any
volume listening functions.