C#绘制图片

public partial class Admin_CheckCode : System.Web.UI.Page
{
    private Bitmap validateimage;
    private Graphics g;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {

            string VNum = MakeValidateCode();
            Session["VNum"] = VNum;
            ValidateCode(VNum);

        }

    }
    public void ValidateCode(string VNum)
    {
        validateimage = new Bitmap(60, 15, PixelFormat.Format24bppRgb);
        g = Graphics.FromImage(validateimage);


        g.FillRectangle(new LinearGradientBrush(new Point(0, 0), new Point(110, 20), Color.FromArgb(240, 255, 255, 255), Color.FromArgb(240, 255, 255, 255)), 0, 0, 200, 200);
        g.DrawString(VNum, new Font("arial", 11), new SolidBrush(Color.Red), new PointF(6, 0));
        g.Save();
        MemoryStream ms = new MemoryStream();
        validateimage.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
        Response.ClearContent();
        Response.ContentType = "image/bmp";
        Response.BinaryWrite(ms.ToArray());
        Response.End();
    }
    string MakeValidateCode()
    {
        char[] s = new char[]{'0','1', '2','3','4','5','6','7','8','9','a'
,'b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q'
,'r','s','t','u','v','w','x','y','z','A','B','C','D','E','F','G'
,'H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W'
,'X','Y','Z'};
        string num = "";
        Random r = new Random();
        for (int i = 0; i < 4; i++)
        {
            num += s[r.Next(0, s.Length)].ToString();
        }
        return num;
    }
}


treeview与imagelist配合使用，使treeview的结点前面多一个图标
1.将imagelist指定给treeview的imagelist属性
2.为每个结点指定一个imageindex，treeview会自动去imagelist里检索相应的图片，另外根结点的索引默认为0
3.在对treeview进行选择操作时，颜色会发生变化，指定每个结点的selectedimageindex与其imageindex一样可以防止这一变化
在添加treenode时指定imagelist的代码如下：
TreeNode SatNode = new TreeNode();
    Icon SatIcon = BuildIcon(sat.DisplayColor.R, sat.DisplayColor.G, sat.DisplayColor.B);
                imageList1.Images.Add(SatIcon);
                SatNode.ImageIndex = imageList1.Images.Count - 1;
                SatNode.SelectedImageIndex = imageList1.Images.Count - 1;
     
为imagelist构建图标的函数如下：   
  Icon BuildIcon(int r, int g, int b)
        {
            int width = imageList1.ImageSize.Width, height = imageList1.ImageSize.Height;
            Bitmap bmp = new Bitmap(width, height, PixelFormat.Format24bppRgb);
            Graphics graphics = Graphics.FromImage(bmp);
            graphics.Clear(Color.FromArgb(r, g, b));
            graphics.Dispose();
            Icon ico = Icon.FromHandle(bmp.GetHicon());
            return ico;
        }
另外，如果修改imagelist中的图标之后，需要刷新treeview才可更新结点前的图标，调用treeview.refresh()即可