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IValidator Interface

Defines the properties and methods that objects that participate in Web Forms validation must implement.

Namespace:  System.Web.UI
Assembly:  System.Web (in System.Web.dll)

public interface IValidator

The IValidator type exposes the following members.

  NameDescription
Public propertyErrorMessageWhen implemented by a class, gets or sets the error message text generated when the condition being validated fails.
Public propertyIsValidWhen implemented by a class, gets or sets a value indicating whether the user-entered content in the specified control passes validation.
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  NameDescription
Public methodValidateWhen implemented by a class, evaluates the condition it checks and updates the IsValid property.
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Classes that implement this interface represent a possible user input error. When the Validate method is called, the class updates its IsValid property to signify whether the error occurred. The ErrorMessage property contains a text description of the error condition that you can display when the error occurs.

The BaseValidator class implements this interface, and all other ASP.NET validation server control classes inherit from BaseValidator. For information on validation server controls and how they work, see ASP.NET Validation Controls.

For details on how to develop custom ASP.NET validation server controls, see How to: Validate with a Custom Function for ASP.NET Server Controls.

Security noteSecurity Note

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.

<!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>IValidator Example demonstrating IsValid & ErrorMessage</title>
<script language="C#" runat="server">

     void Button_Click(Object sender, EventArgs e)
     {
        // Generating the random number.
        Random rand_s = new Random();
        myCompareValidate.ValueToCompare = rand_s.Next(1, 10).ToString();

        // Setting the ErrorMessage.
        myCompareValidate.ErrorMessage="Try Again!!";
        myCompareValidate.Validate();

        // Check for Validity of control.
        if ((myCompareValidate.IsValid) && (myTextBox.Text != ""))
        {
           labelOutput.Text = "You guessed correctly!!";
           labelOutput.ForeColor = System.Drawing.Color.Blue;
        }
        else
        {
           labelOutput.Text =  "You guessed poorly";
           labelOutput.ForeColor = System.Drawing.Color.Black;
        }

        labelOutput.Text += "<br /><br />" + "The number is: " +
           myCompareValidate.ValueToCompare;
     }

  </script>
</head>
    <body>
      <form runat="server" id="myForm">
        <h3>IValidator Example demonstrating IsValid & ErrorMessage</h3>
        <h5>Guess!! a number between 1 and 10 :</h5>
        <asp:TextBox id="myTextBox" runat="server" />
        <asp:CompareValidator id="myCompareValidate"
             ControlToValidate="myTextBox" ValueToCompare="0"
             EnableClientScript="False" Type="Integer" Text="*"
             runat="server" />
        <br />
        <asp:Button Text="Submit" OnClick="Button_Click" runat="server" />
        <br />
        <asp:Label id="labelOutput" runat="server" />
        <br />
        <asp:ValidationSummary id="Summary1" runat="server" />
     </form>
  </body>
</html>

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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