Why is the asp:UpdatePanel not changing the value of my ASP:Textbox when the textbox is updated from Codebehind? – Jquery ajax

My scheme:

• I have a label along with a number of textboxes loaded inside an asp:Updatepanel. These controls are initially loaded with values from an SQL database. These values are based on the initial index passed to the page..
• Additionally the page contains a gridview which contains a list of "contacts".
• The idea is that if the user selects a contact from the gridview, the index is used to re-query the SQL db. This function returns a datatable which is used to populate the above mentioned textboxes with the selected contacts data – name, address, emails, etc. The user can then modify the textboxes as necessary.
• At present, I’m using a asp:timer to trigger the updatepanel when a different contact is selected (though I’d welcome a more elegant trigger solution).

When the page is first loaded, all the controls are populated without issue.

The problem:
When subsequent users are selected, ONLY the label value changes – NOT the textbox values.

What I’ve tried:

• If I disable the timer/trigger, then even the label is not updated when a record is selected in the gridview. This seems to indicate that the timer/trigger is effective (when enabled) as an AsyncPostBackTrigger.
• For the textboxes, I’ve tried variations of how to assign the textbox values (e.g. Textboxt1.text = value; TextBox1.Attributes.Add("value", value1);
• Additionally instead of using an asp:Textbox, I’ve tried using:
  < input type="text" id="TextBox1" runat="server" />

Is what I’m trying to do even possible – what am I missing?

Markup:

<asp:Timer runat="server" ID="Timer1" Interval="400" Enabled="false" OnTick="ContactsTimer_Tick" />
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional" >  
   <ContentTemplate>
      <asp:Label ID="lblContactAccountID" runat="server"/>
      <asp:TextBox ID="txtContactFirstName" runat="server"/> 
      <%--edit: also tried:
      <input type="text"  id="txtContactFirstName" runat="server" />--%>
   </ContentTemplate>
   <Triggers>
      <asp:AsyncPostBackTrigger ControlID="ContactsTimer" EventName="Tick" />
   </Triggers>
</asp:UpdatePanel>

<asp:GridView ID="gvContacts" runat="server" CssClass="table table-striped solid-top" AutoGenerateColumns="false"
   DataKeyNames="PersonID" OnRowCommand="gvContacts_RowSelected">
   <Columns>
      <asp:BoundField DataField="PersonID" />
      <asp:TemplateField HeaderText="Name" ItemStyle-Width="10%" ItemStyle-HorizontalAlign="Center">
         <ItemTemplate>
            <asp:LinkButton runat="server" CommandName="Selected" CommandArgument="<%# Container.DataItemIndex %>"><%#Eval("LastName")%></asp:LinkButton>
            <asp:LinkButton runat="server" CommandName="Selected" CommandArgument="<%# Container.DataItemIndex %>"><%#Eval("FirstName")%></asp:LinkButton>
         </ItemTemplate>
      </asp:TemplateField>
      <asp:TemplateField HeaderText="Action" ItemStyle-Width="10%" ItemStyle-HorizontalAlign="Center">
         <ItemTemplate>
            <asp:ImageButton runat="server" ImageUrl="~/Images/icon_pencil.png" ToolTip='<%# "Edit Profile for "  + Eval("firstname") + " " + Eval("lastname") %>' CommandName="Edit" CommandArgument="<%# Container.DataItemIndex %>" />
         </ItemTemplate>
      </asp:TemplateField>
   </Columns>
</asp:GridView>

Codebehind:

private void LoadSelectedContact(int personID)
{
   DataTable dt = GetProfileContacts(personID, true);
   if (dt.Rows.Count > 0)
   {
      foreach (DataRow row in dt.Rows)
      {
         lblContactAccountID.Text = row["PersonID"].ToString();
         txtContactFirstName.Text = row["FirstName"].ToString();

         // edit: also tried the below without success
         //            string FirstName = row["FirstName"].ToString();
         //            txtContactFirstName.value= FirstName;
         //            txtContactFirstName.Attributes.Add("value", FirstName);


         // ...
         ContactsTimer.Enabled = true;
      }
   }
}

protected void ContactsTimer_Tick(object sender, EventArgs e)
{
   ContactsTimer.Enabled = false;
   upnlContacts.Update();
}

protected void gvContacts_RowSelected(object sender, GridViewCommandEventArgs e)
{
   GridViewRow row;
   if (e.CommandSource.ToString() == "System.Web.UI.WebControls.ImageButton")
   {
      row = (GridViewRow)((ImageButton)e.CommandSource).NamingContainer;
   }
   else
   {
      row = (GridViewRow)((LinkButton)e.CommandSource).NamingContainer;
   }
   int personID = Int32.Parse(row.Cells[0].Text);
   switch (e.CommandName)
   {
      case "Selected":
         LoadSelectedContact(personID);
         break;
      //case "Edit" ...
   }
}