Validation – CustomValidator

In this example, we will simply check the length of the string in the TextBox. This is a very basic and that useful example, only made to show you how you may use the CustomValidator.

<asp:TextBox runat="server" id="txtCustom" />

<asp:CustomValidator runat="server" id="cusCustom" 



    errormessage="The text must be exactly 8 characters long!" />

As you can see, it’s pretty simple. The only unknown property is the onservervalidate event. It’s used to reference a method from CodeBehind which will handle the validation. Switch to our CodeBehind file and add the following method:

protected void cusCustom_ServerValidate(object sender, ServerValidateEventArgs e)


    if(e.Value.Length == 3)

        e.IsValid = true;


        e.IsValid = false;


Hope this will Help you !!!


2 thoughts on “Validation – CustomValidator

  1. its not working for me plz heip my code is

    function Valid(source, args) {
    var PS2 = document.getElementById(”).value;

    var PSLN = PS2.length;
    if (PSLN < 7) {

    args.IsValid = true;
    else {
    args.IsValid = false;

    this code show some runtime error like (Microsoft JScript runtime error: ‘undefined’ is null or not an object)

    tel me sr wt can i do

    • Hi Rohit,
      Problem in statement
      Please make sure that you are providing proper clientid in getElementByID method. and check whether it return object or not by using following statement :
      Alert (document.getElementById(”);

      Hope this will help !!!

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