There
are
times when the validation of your data is so specific to your
application that you will need to write your own validation method.
The CustomValidator is designed to provide all the infrastructure
support you need; you simply point to your validation method and have
it return a Boolean value: true or
false. The CustomValidator control takes care of
all the rest of the work.
Because validation can be done on the client or on the server, depending on the browser, the CustomValidator has attributes for specifying both a server-side and a client-side method for validation. The server-side method can be written in any .NET language, such as C# or VB.NET, while the client-side method must be written in a scripting language understood by the browser, such as VBScript or JavaScript.
You’ll create a simple form that will request an even number from the user, and report the error if the number is not evenly divisible by 2. You can imagine, however, that you could perform a checksum on a credit card or ISBN or otherwise perform complex data checking.
The heart of this example is the CustomValidator control:
<asp:CustomValidator id="cvEven" controlToValidate="txtEven" Display="Static" runat="server" ClientValidationFunction="ClientValidator" OnServerValidate="ServerValidator"> Well, that's odd... </asp:CustomValidator>
The CustomValidator takes many of the usual attributes, such as an
ID, runat,
ControlToValidate, and Display.
In addition, this validator has an attribute that identifies the
script method to run for client-side validation
(ClientValidationFunction
) and one
that defines the method to run for server-side validation
(OnServerValidate
).
You’ll provide JavaScript for the client-side validation:
<script language="javascript">
function ClientValidator(source, value)
{
if (value % 2 == 0)
return true;
else
return false;
}
</script>This simple function examines the value passed to the script by the
validator, and if it is an even number, it returns
true; otherwise, it returns
false. You also
need a
server-side method:
Public Sub ServerValidator(ByVal source As Object, _
ByVal e As ServerValidateEventArgs)
Dim evenNumber As Int32 = Int32.Parse(value)
If evenNumber Mod 2 = 0 Then
e.IsValid = True
Else
e.IsValid = False
End If
End FunctionOr in C#:
public bool ServerValidator (object source, string value)
{
try
{
int evenNumber = Int32.Parse(value);
if (evenNumber % 2 == 0)
return true;
}
catch (Exception)
{
// error handler here
}
return false;
}This method does the same thing as the client-side validator, only in
VB.NETor C# rather than in JavaScript. There are a few things to
notice about these methods. First, the value that the CustomValidator
is examining is passed to your routine as the string parameter
value. You can convert that string to an
int in C# or an Integer in VB.NET using the Base
Class Library Int32 object’s static
Parse method,
as shown. The C# example wraps the conversion in a
try/catch block to handle any
exception that might be thrown.
The complete .aspx file is provided in Example 8-6, with the code-behind file in Example 8-7.
Example 8-6. Custom validator
<%@ Page Language="C#" AutoEventWireup="false" Codebehind="WebForm1.aspx.cs"
Inherits="CustomValidatorVB.WebForm1" EnableSessionState="True"%>
<HTML>
<HEAD>
<meta name=vs_targetSchema content="Internet Explorer 5.0">
<meta name="GENERATOR" Content="Microsoft Visual Studio 7.0">
<meta name="CODE_LANGUAGE" Content="C#">
</HEAD>
<body MS_POSITIONING="GridLayout">
<form method="post" runat="server" ID="Form1">
<table>
<tr>
<td colspan="2">
<h5>Please enter an even number</h5>
</td>
</tr>
<tr>
<td>
<asp:TextBox Width="50" ID="txtEven"
Runat="server" NAME="txtEven"/>
</td>
<td>
<asp:CustomValidator
id="cvEven"
controlToValidate="txtEven"
Display="Static"
runat="server"
ClientValidationFunction="ClientValidator"
OnServerValidate="ServerValidator">
Well, that's odd...
</asp:CustomValidator>
</td>
</tr>
<tr>
<td>
<asp:Button ID="btnValidate" Text="Validate"
Runat="server"></asp:Button>
</td>
<td>
<asp:Label ID="lblMsg" Text="" Runat="server"></asp:Label>
</td>
</tr>
</table>
<script language="javascript">
function ClientValidator(source, value)
{
if (value % 2 == 0)
return true;
else
return false;
}
</script>
</form>
</body>
</HTML>Example 8-7. C# code-behind file for Example 8-6
namespace CustomValidator
{
using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
public class WebForm1 : System.Web.UI.Page
{
protected System.Web.UI.WebControls.TextBox txtEven;
protected System.Web.UI.WebControls.Button btnValidate;
protected System.Web.UI.WebControls.Label lblMsg;
public WebForm1( )
{
Page.Init += new System.EventHandler(Page_Init);
}
protected void Page_Init(object sender, EventArgs e)
{
InitializeComponent( );
}
#region Web Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent( )
{
this.btnValidate.Click += new
System.EventHandler(this.btnValidate_Click);
this.Load += new System.EventHandler(this.Page_Load);
}
#endregion
private void Page_Load(object sender, System.EventArgs e)
{
}
public void ServerValidator (object source, ServerValidateEventArgs e)
{
try
{
int evenNumber = Int32.Parse(e.value);
if (evenNumber % 2 == 0)
e.IsValid = true;
}
catch (Exception)
{
// error handler here
}
}
protected void btnValidate_Click(object sender, System.EventArgs e)
{
if (Page.IsValid)
lblMsg.Text = "Valid.";
else
lblMsg.Text = "Not Valid.";
}
}
}