Untitled

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Timers;
using System.IO;
using System.Security.Cryptography;

namespace BGChanger
{
    class BackgroundChanger
    {
        private string folder;
        private TimeSpan time;
        private Timer changeTimer;

        public TimeSpan Time { get { return this.time; } }
        public string Folder { get { return this.folder; } }

        public delegate void BackgroundChanged(string background);
        public event BackgroundChanged OnBackgroudChanged;

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

        // systemParametersInfo(20, 0, "file", 0x1 | 0x2 );

        public BackgroundChanger(string folder, int days, int hours, int minutes, int seconds)
        {
            this.folder = folder;
            this.time = new TimeSpan(days, hours, minutes, seconds);

            this.changeTimer = new Timer(this.time.TotalMilliseconds);
            this.changeTimer.Elapsed += new ElapsedEventHandler(setRandomBackground);
        }

        public void Start()
        {
            this.changeTimer.Start();
        }

        public void Stop()
        {
            this.changeTimer.Stop();
        }

        private void setRandomBackground(object sender, ElapsedEventArgs e)
        {
            Random rnd = new Random();

            // Build list of possible backgrounds
            List<string> files = new List<string>();
             
            foreach (string str in Directory.GetFiles(this.folder, "*", SearchOption.AllDirectories))
            {
                if (str.EndsWith(".jpg") || str.EndsWith(".jpeg") || str.EndsWith(".png") || str.EndsWith(".bmp"))
                {
                    files.Add(str);
                }
            }

            // "Randomly" select a background
            string bg = files[rnd.Next(0, files.Count - 1)];

            // Set the background
            // systemParametersInfo(20, 0, "file", 0x1 | 0x2);
            SystemParametersInfo(20, 0, bg, 0x1 | 0x2);

            this.OnBackgroudChanged(bg);
        }
    }
}