ASP.NET Tutorial/Validation/BaseValidator

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Create a new validation control by deriving a new control from BaseValidator

   <source lang="csharp">

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" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head id="Head1" runat="server">

   <title>Show Length Validator</title>

</head> <body>

   <form id="form1" runat="server">
   <asp:Label
       id="lblComments"
       Text="Comments:"
       AssociatedControlID="txtComments"
       Runat="server" />
   
<asp:TextBox id="txtComments" TextMode="MultiLine" Columns="30" Rows="2" Runat="server" /> <custom:LengthValidator id="valComments" ControlToValidate="txtComments" Text="(Must be less than 10 characters)" MaximumLength="10" Runat="server" />

<asp:Button id="btnSubmit" Text="Submit" Runat="server" />
   </form>

</body> </html></source>