RadCombobox AJAX functionality issues

From Telerik support:

The behavior you're experiencing is expected due to how the RadComboBox ItemsRequested event works. The ItemsRequested event is triggered by an internal AJAX callback used exclusively for loading items on demand into the RadComboBox. This callback updates only the ComboBox items; it does not update or refresh other controls on the page, even if they are inside a RadAjaxPanel or RadAjaxManager. Changes to controls like lnkNewCustomer or txtTime inside the ItemsRequested handler will not reflect on the client, because the partial update is limited to the ComboBox itself.

Why This Happens

The ItemsRequested event uses a dedicated internal AJAX callback mechanism designed exclusively for loading items on demand. This callback:

• Updates only the ComboBox items
• Does not refresh other controls on the page
• Ignores changes made to controls like lnkNewCustomer or txtTime
• Cannot be intercepted by RadAjaxPanel or RadAjaxManager

This is by design to keep the load-on-demand operation lightweight and efficient.

Solution Options

Option 1: Client-Side Update with OnClientItemsRequested

Use the client-side OnClientItemsRequested event to update controls via JavaScript after items load:

<telerik:RadComboBox ID="cboCustomer" runat="server"

    Width="500px"

    RenderMode="Lightweight"

    AllowCustomText="true"

    AutoPostBack="true"

    DataTextField="custname"

    DataValueField="custnmbr"

    EnableAutomaticLoadOnDemand="true"

    ItemsPerRequest="25"

    OnClientItemsRequested="onItemsRequested">

</telerik:RadComboBox>

<script type="text/javascript">

    function onItemsRequested(sender, eventArgs) {

        // Update LinkButton styling

        var lnkNewCustomer = document.getElementById("<%= lnkNewCustomer.ClientID %>");

        if (lnkNewCustomer) {

            lnkNewCustomer.style.color = "black";

            lnkNewCustomer.style.pointerEvents = "auto";

        }

        // Update RadTextBox

        var txtTime = $find("<%= txtTime.ClientID %>");

        if (txtTime) {

            txtTime.set_value(new Date().toLocaleString());

        }

    }

</script>

Option 2: Trigger a Separate AJAX Postback

Use the client-side event to trigger a hidden button that initiates a proper AJAX postback:

<!-- Add a hidden button inside your RadAjaxPanel -->

<asp:Button runat="server" ID="btnHiddenUpdate" style="display:none" />

<telerik:RadComboBox ID="cboCustomer" runat="server"

    EnableAutomaticLoadOnDemand="true"

    OnClientItemsRequested="triggerServerUpdate">

</telerik:RadComboBox>

<script type="text/javascript">

    function triggerServerUpdate(sender, eventArgs) {

        // Trigger AJAX postback after items are loaded

        __doPostBack('<%= btnHiddenUpdate.UniqueID %>', '');

    }

</script>

Server-side handler (VB.NET):

Private Sub btnHiddenUpdate_Click(sender As Object, e As EventArgs) Handles btnHiddenUpdate.Click

    lnkNewCustomer.Enabled = True

    lnkNewCustomer.ForeColor = System.Drawing.Color.Black

    txtTime.Text = String.Format("{0:MM/dd/yyyy hh:ss:fff}", Now)

End Sub

Option 3: Use Server-Side Mode (Disable Load-On-Demand)

If updating other controls is critical, disable load-on-demand and let RadAjaxPanel handle all updates:

<telerik:RadComboBox ID="cboCustomer" runat="server"

    Width="500px"

    AllowCustomText="true"

    AutoPostBack="true"

    DataTextField="custname"

    DataValueField="custnmbr"

    EnableAutomaticLoadOnDemand="false"

    Filter="Contains">

</telerik:RadComboBox>

Then use TextChanged or SelectedIndexChanged events (which already work) to update controls.

Recommended Approach

Summary

The ItemsRequested event cannot update other controls via server-side code due to its dedicated callback mechanism. Use client-side scripting (OnClientItemsRequested) or trigger a separate AJAX postback to achieve the desired behavior.