Add project files.

Services/ApplicationHostService.cs

@@ -0,0 +1,62 @@
+// This Source Code Form is subject to the terms of the MIT License.
+// If a copy of the MIT was not distributed with this file, You can obtain one at https://opensource.org/licenses/MIT.
+// Copyright (C) Leszek Pomianowski and WPF UI Contributors.
+// All Rights Reserved.
+
+using DownloadManager.Views.Pages;
+using DownloadManager.Views.Windows;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Wpf.Ui;
+
+namespace DownloadManager.Services;
+/// <summary>
+/// Managed host of the application.
+/// </summary>
+public class ApplicationHostService : IHostedService
+{
+    private readonly IServiceProvider _serviceProvider;
+
+    private INavigationWindow _navigationWindow;
+
+    public ApplicationHostService(IServiceProvider serviceProvider)
+    {
+        _serviceProvider = serviceProvider;
+    }
+
+    /// <summary>
+    /// Triggered when the application host is ready to start the service.
+    /// </summary>
+    /// <param name="cancellationToken">Indicates that the start process has been aborted.</param>
+    public async Task StartAsync(CancellationToken cancellationToken)
+    {
+        await HandleActivationAsync();
+    }
+
+    /// <summary>
+    /// Triggered when the application host is performing a graceful shutdown.
+    /// </summary>
+    /// <param name="cancellationToken">Indicates that the shutdown process should no longer be graceful.</param>
+    public async Task StopAsync(CancellationToken cancellationToken)
+    {
+        await Task.CompletedTask;
+    }
+
+    /// <summary>
+    /// Creates main window during activation.
+    /// </summary>
+    private async Task HandleActivationAsync()
+    {
+        if (!Application.Current.Windows.OfType<MainWindow>().Any())
+        {
+            _navigationWindow = (
+                _serviceProvider.GetService(typeof(INavigationWindow)) as INavigationWindow
+            )!;
+            _navigationWindow!.ShowWindow();
+
+            _navigationWindow.Navigate(typeof(Views.Pages.DashboardPage));
+        }
+
+        await Task.CompletedTask;
+    }
+}

Services/PageService.cs

@@ -0,0 +1,45 @@
+// This Source Code Form is subject to the terms of the MIT License.
+// If a copy of the MIT was not distributed with this file, You can obtain one at https://opensource.org/licenses/MIT.
+// Copyright (C) Leszek Pomianowski and WPF UI Contributors.
+// All Rights Reserved.
+
+using Wpf.Ui;
+
+namespace DownloadManager.Services;
+/// <summary>
+/// Service that provides pages for navigation.
+/// </summary>
+public class PageService : IPageService
+{
+    /// <summary>
+    /// Service which provides the instances of pages.
+    /// </summary>
+    private readonly IServiceProvider _serviceProvider;
+
+    /// <summary>
+    /// Creates new instance and attaches the <see cref="IServiceProvider"/>.
+    /// </summary>
+    public PageService(IServiceProvider serviceProvider)
+    {
+        _serviceProvider = serviceProvider;
+    }
+
+    /// <inheritdoc />
+    public T? GetPage<T>()
+        where T : class
+    {
+        if (!typeof(FrameworkElement).IsAssignableFrom(typeof(T)))
+            throw new InvalidOperationException("The page should be a WPF control.");
+
+        return (T?)_serviceProvider.GetService(typeof(T));
+    }
+
+    /// <inheritdoc />
+    public FrameworkElement? GetPage(Type pageType)
+    {
+        if (!typeof(FrameworkElement).IsAssignableFrom(pageType))
+            throw new InvalidOperationException("The page should be a WPF control.");
+
+        return _serviceProvider.GetService(pageType) as FrameworkElement;
+    }
+}