How to set Desktop wallpaper SlideShow with IDesktopWallpaper

Question

I found a class for working with desktop and wallpaper, I can change the background image with the code below

            public static void SetDesktopWallpaper(string imagePath,
                DesktopWallpaperPosition wallpaperPosition)
            {
                IDesktopWallpaper wallpaper = GetWallpaper();
    
                wallpaper.SetPosition(wallpaperPosition);
                wallpaper.SetWallpaper(null, imagePath);
                Marshal.ReleaseComObject(wallpaper);
            }

But I want to use multiple images as slideshow. But I don't know how to do this. I'm not familiar with the slideshow input SetSlideshow(IntPtr items) and I don't know how to give it a list of image addresses

public class DesktopWallpaper
{
    [StructLayout(LayoutKind.Sequential)]
    public struct Rect
    {
        public int Left;
        public int Top;
        public int Right;
        public int Bottom;
    }

    public enum DesktopSlideshowOptions
    {
        ShuffleImages = 0x01
    }

    public enum DesktopSlideshowState
    {
        Enabled = 0x01,
        Slideshow = 0x02,
        DisabledByRemoteSession = 0x04
    }

    public enum DesktopSlideshowDirection
    {
        Forward = 0,
        Backward = 1
    }

    public enum DesktopWallpaperPosition
    {
        Center = 0,
        Tile = 1,
        Stretch = 2,
        Fit = 3,
        Fill = 4,
        Span = 5
    }

    [ComImport, Guid("B92B56A9-8B55-4E14-9A89-0199BBB6F93B"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    public interface IDesktopWallpaper
    {
        void SetWallpaper([MarshalAs(UnmanagedType.LPWStr)] string monitorID, [MarshalAs(UnmanagedType.LPWStr)] string wallpaper);

        [return: MarshalAs(UnmanagedType.LPWStr)]
        string GetWallpaper([MarshalAs(UnmanagedType.LPWStr)] string monitorID);

        [return: MarshalAs(UnmanagedType.LPWStr)]
        string GetMonitorDevicePathAt(uint monitorIndex);

        [return: MarshalAs(UnmanagedType.U4)]
        uint GetMonitorDevicePathCount();

        [return: MarshalAs(UnmanagedType.Struct)]
        Rect GetMonitorRECT([MarshalAs(UnmanagedType.LPWStr)] string monitorID);

        void SetBackgroundColor([MarshalAs(UnmanagedType.U4)] uint color);

        [return: MarshalAs(UnmanagedType.U4)]
        uint GetBackgroundColor();

        void SetPosition([MarshalAs(UnmanagedType.I4)] DesktopWallpaperPosition position);

        [return: MarshalAs(UnmanagedType.I4)]
        DesktopWallpaperPosition GetPosition();

        void SetSlideshow(IntPtr items);

        IntPtr GetSlideshow();

        void SetSlideshowOptions(DesktopSlideshowDirection options, uint slideshowTick);
        [PreserveSig]

        uint GetSlideshowOptions(out DesktopSlideshowDirection options, out uint slideshowTick);

        void AdvanceSlideshow([MarshalAs(UnmanagedType.LPWStr)] string monitorID, [MarshalAs(UnmanagedType.I4)] DesktopSlideshowDirection direction);

        DesktopSlideshowDirection GetStatus();

        bool Enable();
    }

    public static class WallpaperWrapper
    {
        static readonly Guid CLSID_DesktopWallpaper = new Guid("{C2CF3110-460E-4fc1-B9D0-8A1C0C9CC4BD}");

        public static IDesktopWallpaper GetWallpaper()
        {
            Type typeDesktopWallpaper = Type.GetTypeFromCLSID(CLSID_DesktopWallpaper);
            return (IDesktopWallpaper)Activator.CreateInstance(typeDesktopWallpaper);
        }

    }
}

Answer 1

To use multiple images as a SlideShow, you need to create a list with the Paths for those images, and then convert them to a valid IntPtr object as the Interface requires. Please give the code below a go, and see if you're able to achieve your goals:

(I commented most of the stuff so you know what each part of the code is doing)

public static void Main(string[] args)
    {
        IDesktopWallpaper wallpaper = (IDesktopWallpaper)new WallpaperManager();

        List<WallpaperItem> slideshowItems = new List<WallpaperItem>
        {
            new WallpaperItem { Path = @"C:\path\to\image1.jpg", Duration = 10 },
            new WallpaperItem { Path = @"C:\path\to\image2.jpg", Duration = 5 },
            // Add more images with their respective durations.
        };

        // Create a managed array of structures to pass to the COM method.
        var itemsArray = slideshowItems.ToArray();

        // Pin the managed array in memory to get a pointer to it.
        GCHandle itemsHandle = GCHandle.Alloc(itemsArray, GCHandleType.Pinned);
        IntPtr itemsPtr = itemsHandle.AddrOfPinnedObject();

        // Call the SetSlideshow method.
        wallpaper.SetSlideshow(itemsPtr);

        // Release the pinned handle.
        itemsHandle.Free();
    }
}