Thursday 2 September 2010

CustomValidator validation in Repeater with RegisterExpandoAttribute and ClientValidationFunction JavaScript

Hi All,

ASP.Net comes with many validators, one of the validator is CustomValidator. We can use custom validator in 2 ways, either client side or server side validation.

In this post I will provide information specifically on client side validation. Client side validation is achieved with JavaScript function. JavaScript function sample is as below

function MyClientValidation(source, arguments) {
       if ( your validation condition ){
            arguments.IsValid = true;
       } else {
            arguments.IsValid = false;


Now we will call above function with ClientValidationFunction property of custom validator mentioned as below.

   1:  <asp:CustomValidator ID="MyValidator" runat="server" ClientValidationFunction="MyClientValidation"></asp:CustomValidator>


It is simple to call client validation function with a custom validator.

Now you must have question, why I am writing this basic thing for a client validation. Client validation function is really simple when we write validator and control which we are validating both are on page directly. But there is a scenario where this simple method will not work.

In this post I will explain how to use CustomValidator with client side validation when validator is within a Repeater or a ListView control.

We will go through scenario when a CustomValidator is inside a Repeater control. We will have 3 items in Repeater.

  1. A CheckBox control
  2. A TextBox control
  3. And a CustomValidator

Now as per scenario we need to validate TextBox text when check box for same row is selected.

Below will be html for the Repeater:

<asp:Repeater ID="rptItem" runat="server" OnItemDataBound="rptItem_ItemDataBound">
                  <asp:CheckBox ID="chkSelectItem" runat="server" />
                  <asp:TextBox ID="txtToValidate" runat="server"></asp:TextBox>
                  <asp:CustomValidator ID="cValidation" runat="server" ClientValidationFunction="MyClientValidation"

I have registered item data bound event over here to do some code.

We have set the html for our scenario, now custom validator need to validate only those textbox for which corresponding checkbox is selected. We will achieve it with ClientScript.RegisterExpandoAttribute method. ClientScript.RegisterExpandoAttribute is used to register custom attributes for your ASP.Net server controls on runtime. Below is the code to register custom attributes.

protected void rptItem_ItemDataBound(object sender, RepeaterItemEventArgs e)
      if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)
          CheckBox chkSelectItem = e.Item.FindControl("chkSelectItem") as CheckBox;
          TextBox txtToValidate = e.Item.FindControl("txtToValidate") as TextBox;
          CustomValidator cValidation = e.Item.FindControl("cValidation") as CustomValidator;

          if (chkSelectItem != null && txtToValidate != null && cValidation != null)
              ClientScript.RegisterExpandoAttribute(cValidation.ClientID, "chkId", chkSelectItem.ClientID);
              ClientScript.RegisterExpandoAttribute(cValidation.ClientID, "txtId", txtToValidate.ClientID);


Once we register above method in code behind of page and run the page, it will register some script dynamically as below.

var MainContent_rptItem_cValidation_0 = document.all ? document.all["MainContent_rptItem_cValidation_0"] : document.getElementById("MainContent_rptItem_cValidation_0");
MainContent_rptItem_cValidation_0.chkId = "MainContent_rptItem_chkSelectItem_0";
MainContent_rptItem_cValidation_0.txtId = "MainContent_rptItem_txtToValidate_0";
MainContent_rptItem_cValidation_0.errormessage = "Invalid";
MainContent_rptItem_cValidation_0.evaluationfunction = "CustomValidatorEvaluateIsValid";
MainContent_rptItem_cValidation_0.clientvalidationfunction = "MyClientValidation";


Now we need to modify our JavaScript function in such a way that will use our custom registered attributes to validate the control. Modification is as below.

function MyClientValidation(source, arguments) {
      var chkBox = document.getElementById(source.attributes["chkId"].value);
      var txtBox = document.getElementById(source.attributes["txtId"].value);
      if (chkBox.checked == true) {
          var re = new RegExp("[0-9]+");
          if (re.test(txtBox.value)) {
              arguments.IsValid = true;
          else {
              arguments.IsValid = false;
      } else {
          arguments.IsValid = true;


Now we have set all, our validation function will validate textbox with numeric value and non empty and should only validate those textboxes for which checkbox is checked.

Here is the output of our code.


You can modify the JavaScript function as per your requirement. also you can register more expando attributes if you require. But note that it will rendered on the client side and will considerably increase your client script.

Now if you are binding your repeater in an UpdatePanel then you need to register the expando attribute somewhat differently as below

   1:  ScriptManager.RegisterExpandoAttribute(MyUpdatePanel, cValidation.ClientID, "chkId", chkSelectItem.ClientID);
   2:  ScriptManager.RegisterExpandoAttribute(MyUpdatePanel, cValidation.ClientID, "txtId", txtToValidate.ClientID);

Hope you liked this post and it helped you.

Any question or suggestion is welcome.