private async void Startup()
        {
            Uri navigationUri = null;

            switch (Device.OS)
            {
            case TargetPlatform.Android:
                navigationUri = NavigationUriFactory.AbsoluteUri(nameof(DroidRootPage), nameof(SimpleNavigationPage), nameof(FeedPage));
                break;

            case TargetPlatform.iOS:
                navigationUri = NavigationUriFactory.AbsoluteUri(nameof(iOSRootPage), nameof(SimpleNavigationPage), nameof(FeedPage));
                break;

            case TargetPlatform.Windows:
            case TargetPlatform.WinPhone:
                navigationUri = NavigationUriFactory.AbsoluteUri(nameof(UWPRootPage), nameof(SimpleNavigationPage), nameof(FeedPage));
                break;

            case TargetPlatform.Other:
            default:
                break;
            }
            if (navigationUri != null)
            {
                await NavigationService.NavigateAsync(navigationUri);
            }
        }
 private async Task GoTo(IList <string> pageName, bool isModal = false)
 {
     await Navigation.NavigateAsync(NavigationUriFactory.RelativeUri(pageName.ToArray()), useModalNavigation : isModal);
 }