Change your onChange meathod to the following
@Override
public void onChange(boolean selfChange) {
super.onChange(selfChange);
AudioManager audio = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
int currentVolume = audio.getStreamVolume(AudioManager.STREAM_MUSIC);
int delta=previousVolume-currentVolume;
if(delta>0)
{
Logger.d("Decreased");
previousVolume=currentVolume;
}
else if(delta<0)
{
Logger.d("Increased");
previousVolume=currentVolume;
}
}