Export Gridview to Excel in asp.net and c#

aspx code.
<asp:GridView ID="GridView1" runat="server" EnableTheming="False" OnRowDataBound="GridView1_RowDataBound"
Width="100%">
	<HeaderStyle CssClass="ReportHeader" Width="80px" /
	<RowStyle CssClass="ReportText" />
	<PagerStyle CssClass="ReportHeader" />
	<AlternatingRowStyle CssClass="ReportText" />
	<EmptyDataRowStyle CssClass="ReportText" />
	<EmptyDataTemplate>
	    <span style="font-size: 11pt; color: #ff0033"><strong>No Records ........!!</strong></span>
	</EmptyDataTemplate>
<Columns>
    <asp:BoundField HeaderText="Sr. No." />
</Columns>
</asp:GridView>
  
  .cs code

//connection string has written in another class.
string conStr = FetchConnection.FetchConnectionString().ToString();
//Bind Gridview from database
void GridViewEmp()
{
	DataSet Ds = new DataSet();
	SqlDataAdapter mySqlDataAdapter = new SqlDataAdapter();
	string str = "SELECT * from EmployeeTbl"
	Ds = SqlHelper.ExecuteDataset(conStr, CommandType.Text, str);
	GridView1.DataSource = Ds;
	GridView1.DataBind();
}  

protected void lbExportInExcel_Click1(object sender, ImageClickEventArgs e)
    {      
	string attachment = "attachment; filename=" + "Emp Report" + ".xls";
	Response.Clear();
	HttpContext.Current.Response.AddHeader("content-disposition", attachment);
	Response.Charset = "";
	Response.ContentType = "application/vnd.xls";
	System.IO.StringWriter stringWrite = new System.IO.StringWriter();
	System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
	reportName.RenderControl(htmlWrite);       
	rowInfo.RenderControl(htmlWrite);
	rowGridView.RenderControl(htmlWrite);       
	Response.Write(stringWrite.ToString());
	Response.End();     
}
public override void VerifyRenderingInServerForm(Control control)
{
// Confirms that an HtmlForm control is rendered for the
//specified ASP.NET server control at run time.
}