MainWindow.xaml.cs

using Microsoft.UI.Xaml;
using Microsoft.UI.Composition.SystemBackdrops;
using Microsoft.UI.Xaml.Controls;
using Microsoft.UI.Xaml.Controls.Primitives;
using Microsoft.UI.Xaml.Data;
using Microsoft.UI.Xaml.Input;
using Microsoft.UI.Xaml.Media;
using Microsoft.UI.Xaml.Navigation;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using WinRT;

using BootMan.Util;

// To learn more about WinUI, the WinUI project structure,
// and more about our project templates, see: http://aka.ms/winui-project-info.

namespace BootMan
{
    /// <summary>
    /// An empty window that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class MainWindow : Window
    {
        WindowsSystemDispatcherQueueHelper m_wsdqHelper;
        MicaController m_backdropController;
        SystemBackdropConfiguration m_configurationSource;

        public MainWindow()
        {
            this.InitializeComponent();

            // Setup title bar (These can't be set in XAML at the moment)
            Title = Application.Current.Resources["AppWindowTitle"] as string;
            ExtendsContentIntoTitleBar = true;
            SetTitleBar(WindowTitleBar);

            // Use Mica Backdrop
            // See: https://learn.microsoft.com/en-us/windows/apps/windows-app-sdk/system-backdrop-controller
            TrySetSystemBackdrop();
        }

        bool TrySetSystemBackdrop()
        {
            if (Microsoft.UI.Composition.SystemBackdrops.MicaController.IsSupported())
            {
                m_wsdqHelper = new WindowsSystemDispatcherQueueHelper();
                m_wsdqHelper.EnsureWindowsSystemDispatcherQueueController();

                // Create the policy object.
                m_configurationSource = new SystemBackdropConfiguration();
                this.Activated += Window_Activated;
                this.Closed += Window_Closed;
                ((FrameworkElement)this.Content).ActualThemeChanged += Window_ThemeChanged;

                // Initial configuration state.
                m_configurationSource.IsInputActive = true;
                SetConfigurationSourceTheme();

                m_backdropController = new Microsoft.UI.Composition.SystemBackdrops.MicaController();
    
            // Enable the system backdrop.
            // Note: Be sure to have "using WinRT;" to support the Window.As<...>() call.
            m_backdropController.AddSystemBackdropTarget(this.As<Microsoft.UI.Composition.ICompositionSupportsSystemBackdrop>());
                m_backdropController.SetSystemBackdropConfiguration(m_configurationSource);
                return true; // succeeded
            }

            return false; // Mica is not supported on this system
        }

        private void Window_Activated(object sender, WindowActivatedEventArgs args)
        {
            // Handle visual style changes based on window activity state
            m_configurationSource.IsInputActive = args.WindowActivationState != WindowActivationState.Deactivated;
            if (args.WindowActivationState == WindowActivationState.Deactivated)
            {
                AppTitleTextBlock.Foreground =
                    App.Current.Resources["WindowCaptionForegroundDisabled"] as SolidColorBrush;
            }
            else
            {
                AppTitleTextBlock.Foreground =
                    App.Current.Resources["WindowCaptionForeground"] as SolidColorBrush;
            }
        }

        private void Window_Closed(object sender, WindowEventArgs args)
        {
            // Make sure any Mica/Acrylic controller is disposed
            // so it doesn't try to use this closed window.
            if (m_backdropController != null)
            {
                m_backdropController.Dispose();
                m_backdropController = null;
            }
            this.Activated -= Window_Activated;
            m_configurationSource = null;
        }

        private void Window_ThemeChanged(FrameworkElement sender, object args)
        {
            if (m_configurationSource != null)
            {
                SetConfigurationSourceTheme();
            }
        }

        private void SetConfigurationSourceTheme()
        {
            switch (((FrameworkElement)this.Content).ActualTheme)
            {
                case ElementTheme.Dark: m_configurationSource.Theme = Microsoft.UI.Composition.SystemBackdrops.SystemBackdropTheme.Dark; break;
                case ElementTheme.Light: m_configurationSource.Theme = Microsoft.UI.Composition.SystemBackdrops.SystemBackdropTheme.Light; break;
                case ElementTheme.Default: m_configurationSource.Theme = Microsoft.UI.Composition.SystemBackdrops.SystemBackdropTheme.Default; break;
            }
        }

        private void myButton_Click(object sender, RoutedEventArgs e)
        {
            myButton.Content = "Clicked";
        }
    }
}