Validation ASP.Net Tutorial

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  4. Create a new validation control by deriving a new control from BaseValidator
using System;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace myControls
{
    public class LengthValidator : BaseValidator
    {
        int _maximumLength = 0;
        public int MaximumLength
        {
            get { return _maximumLength; }
            set { _maximumLength = value; }
        }
        protected override bool EvaluateIsValid()
        {
            String value = this.GetControlValidationValue(this.ControlToValidate);
            if (value.Length > _maximumLength)
                return false;
            else
                return true;
        }
    }
}
<%@ Page Language="C#" %>
<%@ Register TagPrefix="custom" Namespace="myControls" %>
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">


    Show Length Validator


    
    

            id="lblComments"
        Text="Comments:"
        AssociatedControlID="txtComments"
        Runat="server" />
    
            id="txtComments"
        TextMode="MultiLine"
        Columns="30"
        Rows="2"
        Runat="server" />
            id="valComments"
        ControlToValidate="txtComments"
        Text="(Must be less than 10 characters)"
        MaximumLength="10"
        Runat="server" />
    
            id="btnSubmit"
        Text="Submit"
        Runat="server" />