Create a new website in Visual Studio. Drag and drop GridView control .

In the asp page drag and drop three buttons
<asp:Button ID="exportHTML" runat="server" Text="Export to HTML" OnClick="exportHTML_Click" />
<asp:Button ID="ExportXml" runat="server" Text="Export to XML" OnClick="ExportXml_Click" />
<asp:Button ID="ExportExcel" runat="server" Text="Export to Excel" OnClick="ExportExcel_Click" />

In the code behind page i.e. aspx.cs include the following code
using System.IO;


Export GridView to Html file

protected void exportHTML_Click(object sender, EventArgs e)
{
if (GridView1.DataSource == null)
{
DataSet ds = new DataSet();
ds.ReadXml(Server.MapPath("XMLFile.xml"));
GridView1.DataSource = ds;
GridView1.DataBind();
}
string filename = "ExportToHtml";
Response.ContentType = "text/html";
Response.ContentEncoding = System.Text.Encoding.Unicode;
Response.AddHeader("content-disposition", "attachment; filename=" + filename + ".html");
StringWriter oStringWriter = new StringWriter();
HtmlTextWriter oHtmlTextWriter = new HtmlTextWriter(oStringWriter);
GridView1.RenderControl(oHtmlTextWriter);
Response.Write(oStringWriter.ToString());
Response.End();
}
public override void VerifyRenderingInServerForm(Control control)
{
}

Export GridView to Xml file
protected void ExportXml_Click(object sender, EventArgs e)
{
string filename = "ExportToXml";
DataSet ds = (DataSet)GridView1.DataSource;
if (ds == null)
{
ds = new DataSet();
ds.ReadXml(Server.MapPath("XMLFile.xml"));
GridView1.DataSource = ds;
GridView1.DataBind();
}
Response.ContentType = "text/xml";
Response.AddHeader("content-disposition", "attachment; filename=" + filename+".xml");
ds.WriteXml(Response.OutputStream);
Response.End();
}

Export GridView to Excel file

protected void ExportExcel_Click(object sender, EventArgs e)
{
if (GridView1.DataSource == null)
{
DataSet ds = new DataSet();
ds.ReadXml(Server.MapPath("XMLFile.xml"));
GridView1.DataSource = ds;
GridView1.DataBind();
}
string filename = "ExportToExcel";
Response.ContentType = "application/vnd.ms-excel";
Response.AddHeader("content-disposition", "attachment; filename=" + filename + ".xls");
StringWriter oStringWriter = new StringWriter();
HtmlTextWriter oHtmlTextWriter = new HtmlTextWriter(oStringWriter);
GridView1.RenderControl(oHtmlTextWriter);
Response.Write(oStringWriter.ToString());
Response.End();
}