Question

I’m trying to write a random wallpaper downloader for my desktop.
The code works fine on the first download, but hangs and throws an exception on the
second attempt. I tried to dipose of the client and start with a fresh Web Client.
I also tried without disposing. Thanks in advance.

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

    public static void Main()
    {
        Random fileNumber = new Random();

        string pathStart = "http://www.starcraft2.com/images/screenshots/ss";
        string pathEnd = "-hires.jpg";

        while (true) //forever loop
        {
            string randomFile = fileNumber.Next(1, 126).ToString();

            WebClient Client = new WebClient();

            //OK FIRST TIME -> THROWS EXCEPTION ON SECOND ATTEMPT!
            Client.DownloadFile(pathStart + randomFile + pathEnd, "pic.jpg");

            Client.Dispose(); //tried removing

            Bitmap bm = new Bitmap(Image.FromFile("pic.jpg"));
            bm.Save("pic.bmp", ImageFormat.Bmp);
            bm.Dispose(); //tried removing - no help
            SystemParametersInfo(20, 0, "pic.bmp", 0x01 | 0x02);
            Thread.Sleep(60000); // Sleep for 1 minute
        }
    }
}

Answer 1

Try changing the file name. It’s quite likely that either pic.jpg or pic.bmp still have file locks on them when you are trying the second time. Pick a more unique file name each time.

 Client.DownloadFile(pathStart + randomFile + pathEnd, "pic.jpg");

Probably failing to overwrite pic.jpg. For a test try incrementing the number at during the loop (pic1, pic2, etc.). You can always come up with a better naming scheme later.