Exact character match validation

**Jazz** · 05-18-2006, 05:38 PM

Hi expert, how to write the code of exact character match in a form.
For example I have a text field with 1 character length, and the user can only type in a or b, otherwise the form will pop up errror message. I tried the exact character match like ([Aa]) |([Bb]), but it doesn't work. How to get it correct. Thanks in advance!

**Twey** · 05-18-2006, 05:59 PM

I don't understand. If you have:

Code:

<form action="">
  <input type="text" name="one" maxlength="1">
</form>

You can just use:

Code:

if(document.forms[0].elements['one'].value == "a" || document.forms[0].elements['one'].value == "b") {
  // do whatever
} else {
  window.alert("TEH ERROR");
}

However, <select> elements are better suited to this task.

**Jazz** · 05-18-2006, 07:32 PM

Thanks Twey! But I wrote this program in asp.net. I'm using ValiValidationExpression="[a]||[b]", but it doesn't work.

**Twey** · 05-18-2006, 07:38 PM

In that case, why are you posting in the Javascript forum?

Insofar as I know, the only person here who knows ASP.NET is Otaku, who only pops on from time to time.

If that's regex, however, try (a|b).

**otaku** · 05-18-2006, 08:39 PM

ValidationExpression="[abAB]" will do the job.

**Jazz** · 05-18-2006, 09:30 PM

Thanks! But it doesn't work. The system didn't display any error and let me go when I enter other letters or numbers other than a or b. Would you please tell me what's wrong? Thanks!

**djr33** · 05-18-2006, 11:09 PM

No idea myself, but to save you some time when someone who does checks out this thread,
you should post a link to your page and post your source code.
that will make it a lot easier than guessing at what may or may not be wrong.

**otaku** · 05-18-2006, 11:38 PM

Like djr33 wrote, it's hard to say what's wrong without any code. Here is a small working sample:

Code:

<%@ Page Language="VB" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">
    Protected Sub MyButton_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        Response.Redirect("http://www.dynamicdrive.com")
    End Sub
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Validation Expression Sample</title>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <asp:TextBox ID="MyTextBox" runat="server"></asp:TextBox>
            <asp:Button ID="MyButton" runat="server" Text="GO!" OnClick="MyButton_Click" />
            <asp:RegularExpressionValidator 
                ID="RegExValidator" 
                runat="server" 
                ControlToValidate="MyTextBox"
                ErrorMessage="Your error message here!" 
                ValidationExpression="[abAB]"></asp:RegularExpressionValidator>
        </div>
    </form>
</body>
</html>

Make sure your ControlToValidate match your TextBox ID

**Twey** · 05-19-2006, 12:00 AM

Presuming that conforms to XML rules, you can self-close the asp:RegularExpressionValidator and asp:TextBox tags too.
What does an asp:Button render down into?

**otaku** · 05-19-2006, 02:10 AM

it does not matter if you self close or not in the ASP.Net code, both version will produce the same HTML output:

<input ...... />

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