DisplayMagician/DisplayMagicianShared/Wallpaper.cs

using Microsoft.Win32;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace DisplayMagicianShared
{
    public sealed class Wallpaper
    {
        Wallpaper() { }

        const int SPI_SETDESKWALLPAPER = 20;
        const int SPIF_UPDATEINIFILE = 0x01;
        const int SPIF_SENDWININICHANGE = 0x02;

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        static extern int SystemParametersInfo(int uAction, int uParam, string lpvParam, int fuWinIni);

        public enum Style : int
        {
            Tiled,
            Centered,
            Stretched
        }

        public static void SetAndSave(Uri uri, Style style, string filename)
        {
            System.IO.Stream s = new System.Net.WebClient().OpenRead(uri.ToString());

            System.Drawing.Image img = System.Drawing.Image.FromStream(s);            
            img.Save(filename, System.Drawing.Imaging.ImageFormat.Bmp);

            RegistryKey key = Registry.CurrentUser.OpenSubKey(@"Control Panel\Desktop", true);
            if (style == Style.Stretched)
            {
                key.SetValue(@"WallpaperStyle", 2.ToString());
                key.SetValue(@"TileWallpaper", 0.ToString());
            }

            if (style == Style.Centered)
            {
                key.SetValue(@"WallpaperStyle", 1.ToString());
                key.SetValue(@"TileWallpaper", 0.ToString());
            }

            if (style == Style.Tiled)
            {
                key.SetValue(@"WallpaperStyle", 1.ToString());
                key.SetValue(@"TileWallpaper", 1.ToString());
            }

            SystemParametersInfo(SPI_SETDESKWALLPAPER,
                0,
                filename,
                SPIF_UPDATEINIFILE | SPIF_SENDWININICHANGE);
        }
    }
}