private void PhoneApplicationPage_Loaded(object sender, RoutedEventArgs e) { var visibility = (Visibility)Application.Current.Resources["PhoneLightThemeVisibility"]; if (visibility == Visibility.Visible) { var button = (IApplicationBarIconButton)ApplicationBar.Buttons[1]; button.IconUri=new Uri("H_light.png",UriKind.Relative); } else { var button = (IApplicationBarIconButton)ApplicationBar.Buttons[1]; button.IconUri = new Uri("H_dark.png", UriKind.Relative); } }