Gridview databound event

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C#

ASP.NET

Gridview

I am trying to add a search header within my gridview, however when I render the grdiview databound method, I get a blank page output on the client-side.

I am little unclear where I may be going wrong. I have also debugged the my databound gridview event and the rows parameter is shown to be null. However, I have tested my 'bindgrid' method and this does work (outputs user table).

private void BindGrid()
       {
           string strConnString = ConfigurationManager.ConnectionStrings["cdwConnectionString"].ConnectionString;
           using (SqlConnection con = new SqlConnection(strConnString))
           {
               using (SqlCommand cmd = new SqlCommand())
               {
                   cmd.CommandText = "select top 20 u.[uID], u.[uForenames], u.[uSurname], u.[uCompany], u.[uEmailAddress], s.[sStartDate] from [dbo].[UserDetails]";
                   cmd.Connection = con;
                   con.Open();
                   GridView3.DataSource = cmd.ExecuteReader();
                   GridView3.DataBind();
                   con.Close();
               }
           }
       }


       protected void OnDataBound(object sender, EventArgs e)
       {
           GridViewRow row = new GridViewRow(0, 0, DataControlRowType.Header, DataControlRowState.Normal);
           if (row == null) { return; }

           else
           {
               if (GridView3.Rows.Count > 0) // Add this condition
               {
                   for (int i = 0; i < GridView3.Columns.Count; i++)
                   {
                       TableHeaderCell cell = new TableHeaderCell();
                       TextBox txtSearch = new TextBox();
                       txtSearch.Attributes["placeholder"] = GridView3.Columns[i].HeaderText;
                       txtSearch.CssClass = "search_textbox";
                       cell.Controls.Add(txtSearch);
                       row.Controls.Add(cell);
                   }
                   GridView3.HeaderRow.Parent.Controls.AddAt(1, row);

               }

           }
       }

<asp:gridView ID="GridView3" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
   runat="server" AutoGenerateColumns="false" OnDataBound="OnDataBound">

   </asp:gridView>

Any further advice would be very much appreciated. Many thanks.