Question

I’m surely missing something here, as what I expect to work identically, is working differently.

Suppose the following RegularExpressionValidator syntax

<asp:RegularExpressionValidator runat="server" ID="rxEmail" ControlToValidate="txEmail"
                    ValidationExpression="<%$ appsettings:rxEmail %>" Text="*" />

and the following CustomValidator syntax/code

<asp:CustomValidator ID="cvEmail" runat="server" Text="*" onServerValidate="validateContactFormat" />

Sub validateContactFormat(ByVal sender As Object, ByVal args As ServerValidateEventArgs) Handles cvContactFormat.ServerValidate
        Dim emailRegEx As Regex = New Regex(ConfigurationManager.AppSettings("rxEmail"))
        args.IsValid = emailRegEx.IsMatch(txEmail.Text)

End Sub

The expression held in web.config is

[\w-]+@([\w-]+\.)+[\w-]+

which is supposed to be simple, and weed out the most obvious problems, without being too picky.

Anywho, given the input [e-mail] – the RegularExpressionValidator fails, but the CustomValidator passes. Other scenarios work as expected.. both pass [e-mail], but would fail blah.com. There may be other issues but this is one I noticed.

I guess the code in the CustomValidator isn’t the same as what the RegularExpressionValidator would produce ‘behind the scenes’ – but what exactly is the difference and why do I see what I see?

many thanks!

Answer 1

[e-mail]

contains a dot before the @. That dot isn’t matched by [\w-]+.

The RegularExpressionValidator checks the entire string against the regex and, correctly, fails.

The CustomValidator (using Regex.IsMatch()) checks if a substring matches (and succeeds with [e-mail], again correctly).

To make sure that both behave the same, surround your regex with anchors:

"^(?:" + myOldRegex + ")$"