How Do I Get Data From Database And Place It Is In Dataset Object But Unable To Generate Excel ?

dataset ds=new dataset();
GridView GridView1 = new GridView();
GridView1.AllowPaging = false;
GridView1.DataSource = ds;
GridView1.DataBind();
Response.Clear();
Response.Buffer = true;
Response.AddHeader("content-disposition",
 "attachment;filename=DataTable.xls");
Response.Charset = "";
Response.ContentType = "application/vnd.ms-excel";
StringWriter sw = new StringWriter();
HtmlTextWriter hw = new HtmlTextWriter(sw);
for (int i = 0; i < GridView1.Rows.Count; i++)
{
    GridView1.Rows[i].Attributes.Add("class", "textmode");
}
GridView1.RenderControl(hw);
string style = @"<style> .textmode { mso-number-format:\@; } </style>";
Response.Write(style);
Response.Output.Write(sw.ToString());
Response.Flush();
Response.End();