应客户要求再次开发有滚动条的ASP.Net DataGrid控件 从该例子中可以学习到对VS提供的标准控件进个性开发的思路

				客户要一个有滚动条的ASP.Net DataGrid控件，只好写了：
				
				using System;
				
				using System.Web.UI;
				
				using System.Web.UI.WebControls;
				
				using System.ComponentModel;
				
				using System.Diagnostics;
				
				using System.IO;
				
				using System.Web.UI.Design.WebControls;
				
				using System.Text;
				
				using System.Drawing;
				
				 
				
				[assembly:TagPrefix("Microsoft.Gtec.Dsv", "gtecdsv")] 
				
				namespace Microsoft.Gtec.Dsv
				
				{
				
				  /// 
				
				  /// Summary description for WebCustomControl1.
				
				  /// 
				
				  [ToolboxData("")]
				
				  public class  ScrollableFixedHeaderDataGrid: System.Web.UI.WebControls.DataGrid
				
				  {
				
				    protected override void Render(HtmlTextWriter output)
				
				    {
				
				      //Use this flag to determine whether the component is in design-time or runtime.
				
				      //The control will be rendered differently in IDE.
				
				      //Don't bother to use DataGridDesigner.GetDesignTimeHtml
				
				      bool designMode = ((Site != null) && (Site.DesignMode));
				
				      //Backing up the properties need to change during the render process
				
				      string tempLeft = Style["LEFT"];
				
				      string tempTop = Style["TOP"];
				
				      Unit tempHeight = Height;
				
				      string tempTableStyle = Style["TABLE-LAYOUT"];
				
				 
				
				      //Render a "" container with scrollbars.
				
				      output.WriteBeginTag("div");
				
				      output.WriteAttribute("id",ID + "_div");
				
				      output.WriteAttribute("style",
				
				        "HEIGHT: " + Height + ";" +
				
				        //Leave 20px for the vertical scroll bar,
				
				        //assuming the end-user will not set his scroll bar to more than 20px.
				
				        "WIDTH: " + (Width.Value + 20) + "px;" + 
				
				        "TOP: " + Style["TOP"] + ";" +
				
				        "LEFT: " + Style["LEFT"] + ";" +
				
				        "POSITION: " + Style["POSITION"] + ";" + 
				
				        "OVERFLOW-X: auto;" +
				
				        "Z-INDEX: " + Style["Z-INDEX"] + ";" +
				
				        //Render the scrollbar differently for design-time and runtime.
				
				        "OVERFLOW-Y: " + (designMode?"scroll":"auto")
				
				        );
				
				      output.Write(HtmlTextWriter.TagRightChar);
				
				                        
				
				      //The DataGrid is inside the "" element, so place it at (0,0).
				
				      Style["LEFT"] = "0px";
				
				      Style["TOP"] = "0px";
				
				      //Render the DataGrid.
				
				      base.Render(output);
				
				      output.WriteEndTag("div");
				
				      //Restore the values
				
				      Style["LEFT"] = tempLeft;
				
				      Style["TOP"] = tempTop;
				
				 
				
				      //The following rendering is only necessary under runtime. It has negative impact during design time.
				
				      if (!designMode) 
				
				      {
				
				        //Render another copy of the DataGrid with only headers.
				
				        //Render it after the DataGrid with contents,
				
				        //so that it is on the top. Z-INDEX is more complex here.
				
				        //Set Height to 0, so that it will adjust on its own.
				
				        Height = new Unit("0px");
				
				        StringWriter sw = new StringWriter();
				
				        HtmlTextWriter htw = new HtmlTextWriter(sw);
				
				        //This style is important for matching column widths later.
				
				        Style["TABLE-LAYOUT"] = "fixed";
				
				        base.Render(htw);
				
				        StringBuilder sbRenderedTable = sw.GetStringBuilder();
				
				        htw.Close();
				
				        sw.Close();
				
				        Debug.Assert((sbRenderedTable.Length > 0),
				
				          "Rendered HTML string is empty. Check viewstate usage and databinding.");
				
				        string temp = sbRenderedTable.ToString();
				
				        if (sbRenderedTable.Length > 0)
				
				        {
				
				          //AllowPaging at the top?
				
				          if ((AllowPaging) && ((PagerPosition.Top == PagerStyle.Position || (PagerPosition.TopAndBottom == PagerStyle.Position)))) 
				
				          {
				
				            Trace.WriteLine(temp);
				
				            sbRenderedTable.Replace(ID,ID + "_Pager", 0, (temp.IndexOf(ID) + ID.Length));
				
				            temp = sbRenderedTable.ToString();
				
				            string pager = temp.Substring(0, temp.ToLower().IndexOf(@"") + 5);
				
				            Trace.WriteLine(pager);
				
				            output.Write(pager);
				
				            output.WriteEndTag("table");
				
				            //Start of pager's 
				
				            int start = temp.ToLower().IndexOf(@"				
				            //End of pager's 
				
				            int end = temp.ToLower().IndexOf(@"") + 5;
				
				            //Remove the  for pager from the string. Prepare to render the headers.
				
				            sbRenderedTable.Remove(start,end-start);
				
				            Trace.WriteLine(sbRenderedTable.ToString());
				
				            sbRenderedTable.Replace(ID + "_Pager",ID + "_Headers", 0, (temp.IndexOf(ID+"_Pager") + (ID+"_Pager").Length));
				
				            temp = sbRenderedTable.ToString();
				
				            string tableHeaders = temp.Substring(0, (temp.ToLower()).IndexOf(@"") + 5);
				
				            Trace.WriteLine(tableHeaders);
				
				            output.Write(tableHeaders);
				
				            output.WriteEndTag("table");
				
				            string headerID = ID + "_Headers";
				
				            string pagerID = ID + "_Pager";
				
				            string divID = ID + "_div";
				
				            string adjustWidthScript = @"