The volume control button controls the of setVolumeControlStream description of the audio stream

When developing a multimedia or game application, you need to use the volume control to set the volume of the application. There are multiple audio streams in Android system. The audio stream controlled by the volume control key in Activity can be set through the function setVolumeControlStream(int streamType) in Activity.

The following audio streams are available in Android:

•AudioManager.STREAM_MUSIC /** The audio stream for music playback */
•AudioManager.STREAM_RING /** The audio stream for the phone ring */
•AudioManager.STREAM_ALARM /** The audio stream for alarms */
•AudioManager.STREAM_NOTIFICATION /** The audio stream for notifications */
•AudioManager.STREAM_SYSTEM /** The audio stream for system sounds */
•AudioManager.STREAM_VOICECALL /** The audio stream for phone calls */

setVolumeControlStream function description:

void android.app.Activity .setVolumeControlStream(int streamType)
Suggests an audio stream whose volume should be changed by the hardware volume controls.

The suggested audio stream will be tied to the window of this Activity. If the Activity is switched, the stream set here is no longer the suggested stream. The client does not need to save and restore the old suggested stream value in onPause and onResume.

Parameters:
streamType The type of the audio stream whose volume should be changed by the hardware volume controls. It is not guaranteed that the hardware volume controls will always change this stream's volume (for example, if a call is in progress, its stream's volume may be changed instead). To reset back to the default, use AudioManager.USE_DEFAULT_STREAM_TYPE .