// Callout button tapped
        void mm_Callout_ButtonTapped(object sender, CalloutButtonTappedEventArgs e)
        {
            // Show a message
            headerLabel.Text =  "You tapped on " + e.Annotation.Title;

            // You can Look at e.Annotation to figure out which object's callout was tapped
            if (e.Annotation is Restaurant)
            {
                Restaurant tappedRestaurant = (Restaurant)e.Annotation;
                // Do something with the object here
            }
        }
 void calloutManager_Callout_ButtonTapped(object sender, CalloutButtonTappedEventArgs e)
 {
     if (this.Callout_ButtonTapped != null)
         this.Callout_ButtonTapped(this, e);
 }