//读取文件夹中文件
DirectoryInfo dir = new DirectoryInfo(@"文件夹名");
FileInfo[] fileInfo = dir.GetFiles();
 List<string> fileNames = new List<string>();
foreach (FileInfo item in fileInfo)
{
    fileNames.Add(item.Name);
}

//获取全屏下屏幕分辩率
Rectangle rect = new Rectangle();
//全屏
rect.Width = (int)System.Windows.SystemParameters.PrimaryScreenWidth;
rect.Height = (int)System.Windows.SystemParameters.PrimaryScreenHeight;
//rect = Screen.GetWorkingArea(this);//工作区域下的分辩率，不包括任务栏
//rect.Width;//屏幕宽
//rect.Height;//屏幕高 

/// <summary>
/// 生成缩略图
/// </summary>
/// <param name="serverImagePath">图片地址</param>
/// <param name="thumbnailImagePath">缩略图地址</param>
/// <param name="width">图片宽度</param>
/// <param name="height">图片高度</param>
/// <param name="p"></param>
public static void GetThumbnail(string serverImagePath, string thumbnailImagePath, int width, int height)
{
    System.Drawing.Image serverImage = System.Drawing.Image.FromFile(serverImagePath);
    //画板大小
    int towidth = width;
    int toheight = height;
    //缩略图矩形框的像素点
    int ow = serverImage.Width;
    int oh = serverImage.Height;
    if (ow > oh)
    {
        toheight = serverImage.Height * width / serverImage.Width;
    }
    else
    {
        towidth = serverImage.Width * height / serverImage.Height;
    }
    //新建一个bmp图片
    System.Drawing.Image bm = new System.Drawing.Bitmap(width, height);
    //新建一个画板
    System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bm);
    //设置高质量插值法
    g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
    //设置高质量,低速度呈现平滑程度
    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
    //清空画布并以透明背景色填充
    g.Clear(System.Drawing.Color.White);
    //在指定位置并且按指定大小绘制原图片的指定部分
    g.DrawImage(serverImage, new System.Drawing.Rectangle((width - towidth) / 2, (height - toheight) / 2, towidth, toheight),
        0, 0, ow, oh,
        System.Drawing.GraphicsUnit.Pixel);
    try
    {
        //以jpg格式保存缩略图
        bm.Save(thumbnailImagePath, System.Drawing.Imaging.ImageFormat.Jpeg);
    }
    catch (System.Exception e)
    {
        throw e;
    }
    finally
    {
        serverImage.Dispose();
        bm.Dispose();
        g.Dispose();
    }
}