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CustomValidator.EvaluateIsValid Method

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Definition

Namespace:
System.Web.UI.WebControls
Assembly:
System.Web.dll

Overrides the EvaluateIsValid() method.

protected:
 override bool EvaluateIsValid();
protected override bool EvaluateIsValid ();
override this.EvaluateIsValid : unit -> bool
Protected Overrides Function EvaluateIsValid () As Boolean

Returns

Boolean

true if the value in the input control is valid; otherwise, false.

Examples

The following code example demonstrates how to override the EvaluateIsValid method in a custom server control.

Important

This example has a text box that accepts user input, which is a potential security threat. By default, ASP.NET Web pages validate that user input does not include script or HTML elements. For more information, see Script Exploits Overview.

<%@ Register TagPrefix="aspSample" Namespace="Samples.AspNet.CS.Controls" Assembly="Samples.AspNet.CS" %>
<%@ Page Language="C#" AutoEventWireup="True" %>
<!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>
    <title>Custom CustomValidator - EvaluateIsValid - C# Example</title>
  </head>
<body>
  <form id="Form1" method="post" runat="server">
    <h3>Custom CustomValidator - EvaluateIsValid - C# Example</h3>

    <asp:Label id="Label1" runat="server" Text="Enter an even number:"
      AssociatedControlID="TextBox1" /><br />

    <asp:TextBox id="TextBox1" runat="server" /> 

    <aspSample:CustomCustomValidatorEvaluateIsValid
      id="Customvalidator1"
      runat="server"
      ControlToValidate="TextBox1"
      Display="Static"
      ErrorMessage="Not an even number!" /><br /><br />

    <asp:Button id="Button1" runat="server" Text="Validate" />

  </form>
</body>
</html>

<%@ Register TagPrefix="aspSample" Namespace="Samples.AspNet.VB.Controls" Assembly="Samples.AspNet.VB" %>
<%@ Page Language="VB" AutoEventWireup="True" %>
<!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>
    <title>Custom CustomValidator - EvaluateIsValid - VB.NET Example</title>
  </head>
<body>
  <form id="Form1" method="post" runat="server">
    <h3>Custom CustomValidator - EvaluateIsValid - VB.NET Example</h3>
    <asp:Label id="Label1" runat="server" Text="Enter an even number:"
      AssociatedControlID="TextBox1" /><br />
    <asp:TextBox id="TextBox1" runat="server" /> 
    <aspSample:CustomCustomValidatorEvaluateIsValid id="Customvalidator1" runat="server" ControlToValidate="TextBox1" Display="Static" ErrorMessage="Not an even number!" /><br /><br />
    <asp:Button id="Button1" runat="server" Text="Validate" />
  </form>
</body>
</html>

using System.Web;
using System.Security.Permissions;

namespace Samples.AspNet.CS.Controls
{
    [AspNetHostingPermission(SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Minimal)]
    public sealed class CustomCustomValidatorEvaluateIsValid : System.Web.UI.WebControls.CustomValidator
    {
        protected override bool EvaluateIsValid()
        {
            bool isValid = false;
            
            // Get the name of the control to validate.
            string controlToValidate = this.ControlToValidate;
            if (controlToValidate.Length > 0) 
            {
            // Get the control's value.
            string controlValue = GetControlValidationValue(controlToValidate);

            // If the value is not null and not empty, test whether 
            // check if the value entered into the text box is even,
            // if so return true, else return false in all other cases.
            if ((controlValue != null) && (!controlValue.Trim().Equals(System.String.Empty)))
            {
                try 
                {
                int i = int.Parse(controlValue);
                isValid = ((i%2) == 0);
                }
                catch
                {}
            }  
            } 
            return isValid;   
        }
    }
}

Imports System.Web
Imports System.Security.Permissions

Namespace Samples.AspNet.VB.Controls
    <AspNetHostingPermission(SecurityAction.Demand, Level:=AspNetHostingPermissionLevel.Minimal)> _
    Public NotInheritable Class CustomCustomValidatorEvaluateIsValid
        Inherits System.Web.UI.WebControls.CustomValidator

        Protected Overrides Function EvaluateIsValid() As Boolean
            Dim isValid As Boolean = False

            ' Get the name of the control to validate.
            Dim controlToValidate As String = Me.ControlToValidate
            If controlToValidate.Length > 0 Then

                ' Get the control's value.
                Dim controlValue As String = GetControlValidationValue(controlToValidate)

                ' If the value is not null and not empty, test whether 
                ' check if the value entered into the text box is even,
                ' if so return true, else return false in all other cases.
                If Not (controlValue Is Nothing) AndAlso _
                   Not controlValue.Trim().Equals(System.String.Empty) Then
                    Try
                        Dim i As Integer = Integer.Parse(controlValue)
                        isValid = ((i Mod 2) = 0)
                    Catch
                    End Try
                End If
            End If
            Return isValid
        End Function

    End Class
End Namespace

Applies to