using System.IO;

DirectoryInfo df1 = new DirectoryInfo(Server.MapPath("."));//当前目录
        FileInfo[] f1 = df1.GetFiles("*.xml",SearchOption.TopDirectoryOnly);//只搜索当前目录
        for (int i = 0; i < f1.Length; i++)
        {
            if (f1[i].Extension.ToLower() == ".xml")//检查扩展名
            {
                Response.Write(f1[i].Name + "<br>");
            }
        }

------解决方案--------------------

//public class MyCacheDependency : System.Web.Caching.CacheDependency
//{
//    private FileSystemWatcher watcher;

//    public MyCacheDependency(string filePath)
//    {
//        watcher = new FileSystemWatcher
//        (HttpContext.Current.Server.MapPath(filePath));
//        watcher.EnableRaisingEvents = true;
//        watcher.Created += new FileSystemEventHandler
//        (watcher_Created);
//        watcher.Deleted += new FileSystemEventHandler
//        (watcher_Created);
//        watcher.Changed += new FileSystemEventHandler
//        (watcher_Created);
//    }

//    void watcher_Created(object sender, FileSystemEventArgs e)
//    {
//        if (Path.GetExtension(e.Name) == ".htm" || Path.GetExtension(e.Name) == ".html")
//        {
//            //System.Threading.Thread.Sleep(1000);

//            base.NotifyDependencyChanged(sender, e);
//        }
//    }

//}

这个是以前做文件依赖缓存用得，当添加新文件得时候也能清除缓存，不知道对你有帮助没!