Simulating a RequiredFieldValidator with RadComboBox
Telerik’s RadComboBox does not behave like a traditional DropDownList. Instead of a RequiredFieldValidator, you should use a CustomValidator. Here’s an implementation. Step 1: Markup <asp:Label ID="lblExample" runat="server" AssociatedControlID="rcbExample" Text="Example" /> <telerik:RadComboBox ID="rcbExample" runat="server" /> <asp:CustomValidator ID="cvlExample" runat="server" ControlToValidate="rcbExample" Text="*" ClientValidationFunction="cvlExampleValidate" OnServerValidate="cvlExample_ServerValidate" /> Step 2: Client-side validation function cvlExampleValidate(source, args) { args.IsValid = radComboValidate("<%= rcbExample.ClientID %>"); } function radComboValidate(controlName) { var combo = $find(controlName); var text = combo.get_text(); if (text.length < 1) return false; var node = combo.findItemByText(text); if (node) { var value = node.get_value(); return value.length > 0; } return false; } Step 3: Server-side validation protected void cvlStatus_ServerValidate(object source, ServerValidateEventArgs args) { args.IsValid = rcbStatus.SelectedValue.Length > 0; } Note (2025): This article is from 2010. Telerik’s RadControls have evolved significantly since then; check the current Telerik UI for ASP.NET AJAX documentation for modern practices. ...