how to print gridview data when i click button in asp?

Question

pz give the code help me
i got error my code past below
protected void Page_Load(object sender, EventArgs e)
{
SqlConnection myConnection = new SqlConnection("Data Source=HIMANSHU;Initial Catalog=try;Trusted_Connection=yes;");
SqlDataAdapter Sqlad = new SqlDataAdapter("SELECT * FROM gri", myConnection);
DataSet dsSupplier = new DataSet();
Sqlad.Fill(dsSupplier);
GridView1.DataBind();
}
protected void Button1_Click(object sender, EventArgs e)
{
Response.Clear();
Response.AddHeader("content-disposition", "attachment; filename=SupplierList.xls");
Response.ContentType = "application

/vnd.xls";
System.IO.StringWriter WriteItem = new System.IO.StringWriter();
System.Web.UI.HtmlTextWriter htmlText = new HtmlTextWriter(WriteItem);
GridView1.RenderControl(htmlText);
Response.Write(WriteItem.ToString());
Response.End();
}
i got below error
Control 'GridView1' of type 'GridView' must be placed inside a form tag with runat=server

.
plz help me