Icon on navigation bar for Materdetails page doesn't show on device but simulator

I'm trying to display a settings icon on the navigation bar, and it was successfully shown on ios simulator, but when I deploy it to device, and icon was disappeared.

Any one have any suggestion?

  `public partial class MainPage : MasterDetailPage
  {
        public MainPage()
        {
            InitializeComponent();

            BindingContext = new ViewModelMainPage();

            Icon = "settings.png";

            Detail = new NavigationPage(new DetailsPage(...));
          }
     }`