How to stop playing music when the smartphone application starts (iOS/Android)

var player=MediaPlayer.MPMusicPlayerController.iPodMusicPlayer;
if(player.PlaybackState==MediaPlayer.MPMusicPlaybackState.Playing)
{
    player.Pause();
}

 var session=AVFoundation.AVAudioSession.SharedInstance();
NSError error;
session.SetActive(true, outerr);

public class MainActivity: Activity, Android.Media.AudioManager.IonAudioFocusChangeListener
{
    Android.Media.AudioManager_audioManager;

    protected override void OnResume()
    {
        base.OnResume();

        _audioManager= (Android.Media.AudioManager) GetSystemService (Context.AudioService);

        // exclusively deprive someone of focus
        _audioManager.RequestAudioFocus(this, Android.Media.Stream.Music, Android.Media.AudioFocus.GainTransientExclusive);
    }

    public void OnAudioFocusChange([GeneratedEnum] Android.Media.AudioFocus FocusChange)
    {
       // be called when one gets focus
    }

    protected override void OnPause()
    {
        // relinquish focus
        _audioManager.AbandonAudioFocus(this);
        base.OnPause();
    }
}