Add chapter 10 sample project

Chapter10/TemplateStudioSampleApp/Services/ActivationService.cs

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+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+
+using TemplateStudioSampleApp.Activation;
+using TemplateStudioSampleApp.Contracts.Services;
+using TemplateStudioSampleApp.Views;
+
+namespace TemplateStudioSampleApp.Services;
+
+public class ActivationService : IActivationService
+{
+    private readonly ActivationHandler<LaunchActivatedEventArgs> _defaultHandler;
+    private readonly IEnumerable<IActivationHandler> _activationHandlers;
+    private readonly IThemeSelectorService _themeSelectorService;
+    private UIElement? _shell = null;
+
+    public ActivationService(ActivationHandler<LaunchActivatedEventArgs> defaultHandler, IEnumerable<IActivationHandler> activationHandlers, IThemeSelectorService themeSelectorService)
+    {
+        _defaultHandler = defaultHandler;
+        _activationHandlers = activationHandlers;
+        _themeSelectorService = themeSelectorService;
+    }
+
+    public async Task ActivateAsync(object activationArgs)
+    {
+        // Execute tasks before activation.
+        await InitializeAsync();
+
+        // Set the MainWindow Content.
+        if (App.MainWindow.Content == null)
+        {
+            _shell = App.GetService<ShellPage>();
+            App.MainWindow.Content = _shell ?? new Frame();
+        }
+
+        // Handle activation via ActivationHandlers.
+        await HandleActivationAsync(activationArgs);
+
+        // Activate the MainWindow.
+        App.MainWindow.Activate();
+
+        // Execute tasks after activation.
+        await StartupAsync();
+    }
+
+    private async Task HandleActivationAsync(object activationArgs)
+    {
+        var activationHandler = _activationHandlers.FirstOrDefault(h => h.CanHandle(activationArgs));
+
+        if (activationHandler != null)
+        {
+            await activationHandler.HandleAsync(activationArgs);
+        }
+
+        if (_defaultHandler.CanHandle(activationArgs))
+        {
+            await _defaultHandler.HandleAsync(activationArgs);
+        }
+    }
+
+    private async Task InitializeAsync()
+    {
+        await _themeSelectorService.InitializeAsync().ConfigureAwait(false);
+        await Task.CompletedTask;
+    }
+
+    private async Task StartupAsync()
+    {
+        await _themeSelectorService.SetRequestedThemeAsync();
+        await Task.CompletedTask;
+    }
+}