CustomValidator for login page (VB) : CustomValidator « Validation « ASP.NET Tutorial

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
  <head>
    <title>CustomValidator Control Sample</title>
    <script runat="server" language="VB">
      Sub CheckUniqueUserName(s As Object, _
            e As ServerValidateEventArgs)
        Dim username As String = e.Value.ToLower
        If (username = "user" Or username = "password") Then
          e.IsValid = False
        End If
      End Sub
      
      Sub submitButton_Click(s As Object, e As EventArgs)
        If Page.IsValid Then
          submitButton.Text = "Valid"
        Else
          submitButton.Text = "Invalid!"
        End If
      End Sub
    </script>
  </head>
  <body>
    <form id="Form1" runat="server">
      
        New Username:<br />
        <asp:TextBox ID="usernameTextBox" runat="server" />
        <asp:CustomValidator ID="usernameUnique" runat="server"
            ControlToValidate="usernameTextBox"
            OnServerValidate="CheckUniqueUserName"
            ErrorMessage="This username already taken!" />
      
      
        <asp:Button ID="submitButton" runat="server"
            OnClick="submitButton_Click" Text="Submit" />
      
    </form>
  </body>
</html>

8.3.CustomValidator
	8.3.1.	You can associate a custom validation function with the CustomValidator control.
	8.3.2.	Validate a blank field
	8.3.3.	Performing validation against no particular field.
	8.3.4.	Use both client side and server side script to validate (VB.net)
	8.3.5.	Create user control based on CustomValidator
	8.3.6.	Using the CustomValidator control to perform client-side validations
	8.3.7.	Using the CustomValidator control to perform server-side validations (C#)
	8.3.8.	Using the CustomValidator control to perform server-side validations (VB)
	8.3.9.	Custom validator with Javascript
	8.3.10.	CustomValidator for login page
	8.3.11.	CustomValidator for login page (VB)