DropDownList ใน Gridview ไม่ยอมเปลี่ยนค่าค่ะ จะโชว์แต่ค่าแรกเสมอ asp.net

 protected void GridView1_RowDataBound(Object s, GridViewRowEventArgs e)
    {


        //*** Hyperlink ***//
        HyperLink htno = (HyperLink)(e.Row.FindControl("htno"));
        if (htno != null)
        {
           // htno.Text = Convert.ToString(DataBinder.Eval(e.Row.DataItem, "No"));
            htno.NavigateUrl = "Default2.aspx?id=" + Convert.ToString(DataBinder.Eval(e.Row.DataItem, "No"));
        }
        //*** Hyperlink ***//
        HyperLink htid = (HyperLink)(e.Row.FindControl("htid"));
        if (htid != null)
        {
            //htid.Text = Convert.ToString(DataBinder.Eval(e.Row.DataItem, "Id"));
            htid.NavigateUrl = "Default2.aspx?id=" + Convert.ToString(DataBinder.Eval(e.Row.DataItem, "No"));
        }
}

code ในปุ่ม ส่งค่าแสดงที่Label
  protected void Button1_Click(object sender, EventArgs e)
        {
            
            DropDownList LabelNote;
            HyperLink LabelNo;
           
            int i;
          
            Label3.Text = "";
            Label4.Text = "";
            Label5.Text = "";
            for (i = 0; i <= GridView1.Rows.Count - 1; i++)
            {
              
                LabelNo = (HyperLink)GridView1.Rows[i].FindControl("htno");
                LabelNote = (DropDownList)GridView1.Rows[i].FindControl("DropDownList1");



                this.Label3.Text = this.Label3.Text + "<br>" + LabelNo.Text;
                this.Label4.Text = this.Label4.Text + "<br>" + Convert.ToString(LabelNote.SelectedItem);

                             
            }        
        
    }