Mica support in .NET MAUI

MauiProgram.cs

// ************************************************************************ //
// This implementation is inspired from the official WinUI3 backdrops examples
// https://github.com/microsoft/WinUI-Gallery/blob/winui3/XamlControlsGallery/ControlPagesSampleCode/SystemBackdrops/SystemBackdropsSample2.txt
// *********************************************************************** //

using Microsoft.Maui.LifecycleEvents;

#if WINDOWS10_0_17763_0_OR_GREATER
// The namespace of where the WindowsHelpers class resides
// In older versions of .NET MAUI, this was
//using YOUR_APP.Platforms.Windows
// In newer versions of .NET MAUI, it is now
using YOUR_APP.WinUI;
#endif

namespace YOUR_APP.Maui
{
    public static class MauiProgram
    {
        public static MauiApp CreateMauiApp()
        {
            var builder = MauiApp.CreateBuilder();
            builder
                .UseMauiApp<App>()
                .ConfigureFonts(fonts =>
                {
                    fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
                    fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
                });

        // **** THIS SECTION IS WHAT IS RELEVANT FOR YOU ************ //
        builder.ConfigureLifecycleEvents(events =>
        {
#if WINDOWS10_0_17763_0_OR_GREATER

            events.AddWindows(wndLifeCycleBuilder =>
            {
                wndLifeCycleBuilder.OnWindowCreated(window =>
                {
                    window.TryMicaOrAcrylic(); // requires 'using YOUR_APP.WinUI;'
                });
            });
#endif
        });
        // ************* END OF RELEVANT SECTION *********** //

            return builder.Build();
        }
    }
}

WindowHelpers.cs

// **************************************************** //
// Place this class file in your Platforms/Windows folder
// **************************************************** //

using Microsoft.UI.Composition;
using Microsoft.UI.Composition.SystemBackdrops;
using Microsoft.UI.Xaml;
using WinRT;

namespace YOUR_APP.Platforms.Windows
{
    public static class WindowHelpers
    {
        public static void TryMicaOrAcrylic(this Microsoft.UI.Xaml.Window window)
        {
            var dispatcherQueueHelper = new WindowsSystemDispatcherQueueHelper(); // in Platforms.Windows folder
            dispatcherQueueHelper.EnsureWindowsSystemDispatcherQueueController();

            // Hooking up the policy object
            var configurationSource = new SystemBackdropConfiguration();
            configurationSource.IsInputActive = true;

            switch (((FrameworkElement)window.Content).ActualTheme)
            {
                case ElementTheme.Dark:
                    configurationSource.Theme = SystemBackdropTheme.Dark; 
                    break;
                case ElementTheme.Light:
                    configurationSource.Theme = SystemBackdropTheme.Light;
                    break;
                case ElementTheme.Default:
                    configurationSource.Theme = SystemBackdropTheme.Default;
                    break;
            }
            
            // Let's try Mica first
            if (MicaController.IsSupported()) 
            {
                var micaController = new MicaController();
                micaController.AddSystemBackdropTarget(window.As<ICompositionSupportsSystemBackdrop>());
                micaController.SetSystemBackdropConfiguration(configurationSource);
                
                window.Activated += (object sender, WindowActivatedEventArgs args) =>
                {
                    if (args.WindowActivationState is WindowActivationState.CodeActivated or WindowActivationState.PointerActivated)
                    {
                        // Handle situation where a window is activated and placed on top of other active windows.
                        if (micaController == null)
                        {
                            micaController = new MicaController();
                            micaController.AddSystemBackdropTarget(window.As<ICompositionSupportsSystemBackdrop>()); // Requires 'using WinRT;'
                            micaController.SetSystemBackdropConfiguration(configurationSource);
                        }

                        if (configurationSource != null)
                            configurationSource.IsInputActive = args.WindowActivationState != WindowActivationState.Deactivated;
                    }
                };

                window.Closed += (object sender, WindowEventArgs args) =>
                {
                    if (micaController != null)
                    {
                        micaController.Dispose();
                        micaController = null;
                    }

                    configurationSource = null;
                };
            }
            // If no Mica, maybe we can use Acrylic instead
            else if (DesktopAcrylicController.IsSupported())
            {
                var acrylicController = new DesktopAcrylicController();
                acrylicController.AddSystemBackdropTarget(window.As<ICompositionSupportsSystemBackdrop>());
                acrylicController.SetSystemBackdropConfiguration(configurationSource);

                window.Activated += (object sender, WindowActivatedEventArgs args) =>
                {
                    if (args.WindowActivationState is WindowActivationState.CodeActivated or WindowActivationState.PointerActivated)
                    {
                        // Handle situation where a window is activated and placed on top of other active windows.
                        if (acrylicController == null)
                        {
                            acrylicController = new DesktopAcrylicController();
                            acrylicController.AddSystemBackdropTarget(window.As<ICompositionSupportsSystemBackdrop>()); // Requires 'using WinRT;'
                            acrylicController.SetSystemBackdropConfiguration(configurationSource);
                        }
                    }

                    if (configurationSource != null)
                        configurationSource.IsInputActive = args.WindowActivationState != WindowActivationState.Deactivated;
                };

                window.Closed += (object sender, WindowEventArgs args) =>
                {
                    if (acrylicController != null)
                    {
                        acrylicController.Dispose();
                        acrylicController = null;
                    }

                    configurationSource = null;
                };
            }
        }
    }
}

WindowsSystemDispatcherQueueHelper.cs

// **************************************************** //
// Place this class file in your Platforms/Windows folder
// **************************************************** //

using System.Runtime.InteropServices;
using Windows.System; // Required for DllImport attribute and DispatcherQueue

namespace YOUR_APP.Maui.Platforms.Windows;

public class WindowsSystemDispatcherQueueHelper
{
    [StructLayout(LayoutKind.Sequential)]
    struct DispatcherQueueOptions
    {
        internal int dwSize;
        internal int threadType;
        internal int apartmentType;
    }

    [DllImport("CoreMessaging.dll")]
    private static extern int CreateDispatcherQueueController([In] DispatcherQueueOptions options, [In, Out, MarshalAs(UnmanagedType.IUnknown)] ref object dispatcherQueueController);

    object m_dispatcherQueueController = null;

    public void EnsureWindowsSystemDispatcherQueueController()
    {
        if (DispatcherQueue.GetForCurrentThread() != null)
        {
            // one already exists, so we'll just use it.
            return;
        }

        if (m_dispatcherQueueController == null)
        {
            DispatcherQueueOptions options;

            options.dwSize = Marshal.SizeOf(typeof(DispatcherQueueOptions));
            options.threadType = 2;    // DQTYPE_THREAD_CURRENT
            options.apartmentType = 2; // DQTAT_COM_STA

            CreateDispatcherQueueController(options, ref m_dispatcherQueueController);
        }
    }
}

@ajsuydam While I was still working on that project, I found some references to creating custom renderes for components. In those articles, which I don’t have handy, they mentioned that you can override the rendering of a built in component by inheriting from it. However I have since had to move off that project, and never tested the suggested approach.
perhaps you can dive into that rabbit hole and keep us posted.

Just watched this vid, and it seems to point in the right direction for overriding or defining custom behavior on default controls or custom ones.
https://www.youtube.com/live/tOCh0d4PpOw?si=H4LClSKD37epxtzb

This has been a long time coming. To all who are still trying to solve this issue... it's done.

full sample: https://github.com/kolkonos/MicaBackdropMAUI

As Lance mentioned, add the mica effect during the lifecycle event. I prefer the MikaKind.BaseAlt as it is more pronounced (more vivid color).

THEN in the AppShell.xaml.cs in the class constructor:

public partial class AppShell : Shell
{
    public AppShell()
    {
        InitializeComponent();

        this.Loaded += (_, _) => {
#if WINDOWS        
          var shellView = `Shell.Current?.Handler?.PlatformView` as ShellView;
          var navigationView = shellView?.Content as MauiNavigationView;

          var contentGrid = navigationView?.GetType()
              .GetProperty("ContentGrid", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance)?
              .GetValue(navigationView) as Microsoft.UI.Xaml.Controls.Grid;

          contentGrid!.Background.Opacity = 0;
#endif
       };
}

It's crucial that you set the opacity to 0 rather than setting the Background to null, as this would cause the framework to fallback to the default.
@ajsuydam

@kolkonos BOOM! Looks great.