GridView deki datayı excele aktarmak

private void Button1_Click(object sender, System.EventArgs e)
{
//export to excel

Response.Clear();
Response.Buffer= true;
Response.ContentType = "application/vnd.ms-excel";
Response.Charset = "";
this.EnableViewState = false;

System.IO.StringWriter oStringWriter = new System.IO.StringWriter();
System.Web.UI.HtmlTextWriter oHtmlTextWriter = new System.Web.UI.HtmlTextWriter(oStringWriter);

this.ClearControls(dg);
dg.RenderControl(oHtmlTextWriter);

Response.Write(oStringWriter.ToString());

Response.End();
}