Create New Validator Control in ASP.NET

Posted: December 5, 2010 in ASP.NET
Tags: , ,

ListValidator.cs Code

public class ListValidator : BaseValidator
public ListValidator()

protected override bool ControlPropertiesValid()
Control ctrl = FindControl(ControlToValidate) as ListControl;
return (ctrl != null);

protected override bool EvaluateIsValid()
return this.CheckIfItemIsChecked();

protected bool CheckIfItemIsChecked()
ListControl listItemValidate = ((ListControl)this.FindControl(this.ControlToValidate));
foreach (ListItem listItem in listItemValidate.Items)
if (listItem.Selected == true)
return true;
return false;

protected override void OnPreRender(EventArgs e)
// Determines whether the validation control can be rendered
// for a newer (“uplevel”) browser.
// check if client-side validation is enabled.
if (this.DetermineRenderUplevel() && this.EnableClientScript)
Page.ClientScript.RegisterExpandoAttribute(this.ClientID, “evaluationfunction”, “CheckIfListChecked”);

protected void CreateJavaScript()
StringBuilder sb = new StringBuilder();
sb.Append(@”<script type=””text/javascript””>function CheckIfListChecked(ctrl){“);
sb.Append(@”var chkBoxList = document.getElementById(document.getElementById(;”);
sb.Append(@”var chkBoxCount= chkBoxList.getElementsByTagName(“”input””);”);
sb.Append(@”for(var i=0;i<chkBoxCount.length;i++){“);
sb.Append(@”return true; }”);
sb.Append(@”}return false; “);
Page.ClientScript.RegisterClientScriptBlock(GetType(), “JSScript”, sb.ToString());

Custom Validator Control – Usage – Client Side

<%@ Register TagPrefix=”CLV” Namespace=”WebApplication1.Concepts.Validators” assembly=”WebApplication1″%>

<form id=”form1″ runat=”server”>
<asp:CheckBoxList ID=”CheckBoxList1″ runat=”server”></asp:CheckBoxList>
<CLV:ListValidator runat=”server” ID=”custLstVal” ControlToValidate=”CheckBoxList1″ ErrorMessage=”At least one item in the checkboxlist should be checked”
<asp:RadioButtonList ID=”RadioButtonList1″ runat=”server”></asp:RadioButtonList>
<CLV:ListValidator runat=”server” ID=”custRadVal” ControlToValidate=”RadioButtonList1″ ErrorMessage=”At least one item in the radiobuttonlist should be checked”
<br />
<br />
<asp:Button ID=”Button1″ runat=”server”  Text=”Button” />

Web Page Code Behind Code

protected void Page_Load(object sender, EventArgs e)
if (!Page.IsPostBack)
List<string> lstStr = new List<string>();
lstStr.Add(“Item 1”);
lstStr.Add(“Item 2”);
lstStr.Add(“Item 3”);
lstStr.Add(“Item 4”);
CheckBoxList1.DataSource = lstStr;
RadioButtonList1.DataSource = lstStr;


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