App.xaml.cs

using System;

using Windows.ApplicationModel.Activation;
using Windows.UI;
using Windows.UI.ViewManagement;
using Windows.UI.Xaml;

using FlarumUWP.Services;

namespace FlarumUWP
{
    public sealed partial class App : Application
    {
        private Lazy<ActivationService> _activationService;

        private ActivationService ActivationService
        {
            get { return _activationService.Value; }
        }

        public App()
        {
            InitializeComponent();
            UnhandledException += OnAppUnhandledException;

            // Deferred execution until used. Check https://docs.microsoft.com/dotnet/api/system.lazy-1 for further info on Lazy<T> class.
            _activationService = new Lazy<ActivationService>(CreateActivationService);
        }

        protected override async void OnLaunched(LaunchActivatedEventArgs args)
        {
            var coreTitleBar = Windows.ApplicationModel.Core.CoreApplication.GetCurrentView().TitleBar;
            var appTitleBar = Windows.UI.ViewManagement.ApplicationView.GetForCurrentView().TitleBar;
            coreTitleBar.ExtendViewIntoTitleBar = false;

            /*coreTitleBar.ExtendViewIntoTitleBar = true;
            appTitleBar.ButtonBackgroundColor = Colors.Transparent;*/
            var uiSettings = new UISettings();
            //appTitleBar.ButtonForegroundColor = uiSettings.GetColorValue(UIColorType.Background);

            if (!args.PrelaunchActivated)
            {
                await ActivationService.ActivateAsync(args);
            }
        }
        private void UpdateAccentColorForeground(FrameworkElement element)
        {
            var uiSettings = new UISettings();
            Color c = uiSettings.GetColorValue(UIColorType.Accent);

            element.RequestedTheme = ((5 * c.G + 2 * c.R + c.B) <= 8 * 128)
                ? ElementTheme.Light
                : ElementTheme.Dark;
        }

        protected override async void OnActivated(IActivatedEventArgs args)
        {
            await ActivationService.ActivateAsync(args);
        }

        private void OnAppUnhandledException(object sender, Windows.UI.Xaml.UnhandledExceptionEventArgs e)
        {
            e.Handled = true;
            _ = e.Message;
        }

        private ActivationService CreateActivationService()
        {
            return new ActivationService(this, typeof(Views.HomePage), new Lazy<UIElement>(CreateShell));
        }

        private UIElement CreateShell()
        {
            return new Views.ShellPage();
        }
    }
}