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Example 16 customValidation.aspx

<%@ Page Language="VB" %>

<html>

<head>

Sub ValidateBtn_OnClick (sender As object, e As EventArgs)

If Page.IsValid Then

lblOutput. Text = "Page is valid."

Else

lblOutput.Text = "Page is not valid!"

End If

End Sub

Sub ServerValidation (source As object, arguments As ServerValidateEventArgs)

Dim num As Integer = Integer.Parse(arguments.Value)

arguments. IsValid = ((num mod 2) = 0)

End Sub

</script>

</head>

<body>

<h3>CustomValidator Example</h3>

<asp:Label id=lblOutput runat="server"

Text="Enter an even number:"

Font-Name="Verdana"

Font-Size="10pt" /><br>

<p>

<asp:TextBox id="Text1"

runat="server" />

<asp:CustomValidator id="CustomValidator1"

ControlToValidate="Text1"

OnServerValidate="ServerValidation"

Display="Static"

ErrorMessage="Not an even number!"

ForeColor="green"

Font-Name="verdana"

Font-Size="10pt"

runat="server"/>

<p>

<asp:Button id="Button1"

Text="Validate"

OnClick="ValidateBtn_OnClick"

runat="server"/>

</form>

</body>

</html>

The output of this example is shown below:

The above example demonstrates how to create a CustomValidation control that validates whether the value entered in a text box is an even number on the server. The validation result is then displayed on the page.

The CustomValidatorcontrol allows creating a validation control with customized validation logic. In above example, a validation control can be created that check whether the value entered into a text box is an even number.

Validation controls always perform validation checking on the server. They also have complete client-side implementation that allows DHTML-supported browsers (such as Microsoft Internet Explorer 4.0 or later) to perform validation on the client. Client-side validation enhances the validation process by checking user input before it is sent to the server. This allows errors to be detected on the client before the form is submitted, avoiding the round-trip of information necessary for server-side validation.

To create a server-side validation function, provide a handler for the ServerValidate event that performs the validation. The string from the input control to validate can be accessed by using the Value property of the ServerValidateEventArgs object passed into the event handler as a parameter. The result of the validation is then stored in the IsValid property of the ServerValidateEventArgs object.

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