RegisterReceiver(new BroadcastReceivers.Media_Button(), new IntentFilter(Intent.ActionMediaButton));

ComponentName myEventReceiver = new ComponentName(this, nameof(Media_Button));
AudioManager myAudioManager = (AudioManager) this.GetSystemService(Context.AudioService);
myAudioManager.RegisterMediaButtonEventReceiver(myEventReceiver);
Intent mediaButtonIntent = new Intent(Intent.ActionMediaButton);
mediaButtonIntent.SetComponent(myEventReceiver);
PendingIntent mediaPendingIntent = PendingIntent.GetBroadcast(this, 0, mediaButtonIntent, 0);
// create and register the remote control client
RemoteControlClient myRemoteControlClient = new RemoteControlClient(mediaPendingIntent);
myAudioManager.RegisterRemoteControlClient(myRemoteControlClient);

[BroadcastReceiver(Enabled = true, Label = "Media Button Receiver")]
[IntentFilter(new[] { "android.intent.action.MEDIA_BUTTON" })]
class Media_Button : BroadcastReceiver
{
    public override void OnReceive(Context context, Intent intent)
    {
        Console.WriteLine("----------Detected media button--------------");
    }
}