how to use RegularExpressionValidator on textbox - asp.net

Question

I have an text box i need to validate so that the user can enter enter up to four character and they can be alphanumeric. I am using VS2003, .NET 1.1.
Please let me know what is the expression i should use to validate this condition
any help would be great. Thanks!
Tried like this:
<asp:TextBox id="wtxtTPP" tabIndex="2" runat="server" CssClass="text" Width="144px" MaxLength="4" />
<asp:RegularExpressionValidator id="RegularExpressionValidator1" style="z-index: 101; left: 208px; position: absolute; TOP: 16px" runat="server" ErrorMessage="RegularExpressionValidator" ValidationExpression="^([\S\s]{0,4})$" ControlToValidate="wtxtTPP" />
<input style="z-index: 102; left: 88px; position: absolute; top: 72px" type="submit" value="Submit" id="Submit1" name="Submit1" runat="server">

Answer 1

As you said, use a Regular Expression Validator and set the expression to something like this:
^([\S\s]{0,4})$
Replace the 4 with your desired max length.
Update:
<asp:TextBox id="wtxtTPP" Runat="server" />
<asp:RegularExpressionValidator id="RegularExpressionValidator1" runat="server"
ErrorMessage="RegularExpressionValidator"
ValidationExpression="^([\S\s]{0,4})$"
ControlToValidate="wtxtTPP" />
<asp:Button ID="Button1" runat="server" Text="Button" />
This works just fine for me. I replaced your submit button with a normal asp.net button and simplified out all the unneeded stuff for the example.
In general, if you only have a one line textbox, you can just limit the text length with MaxLength="4" as you did. No need for a Validator.

Answer 2

Like #Remy said.
Also, the {0,4} part of the Regexp means length should be zero to a max of four so will allow for zero-length, i.e. no input. Remember to use a RequiredFieldValidator if the number is mandatory or replace the zero with a minimum number of digits.

Answer 3

<table>
<tr>
<td>E-mail Address:</td>
<td>
<asp:TextBox ID="txt_address" runat="server"></asp:TextBox>
</td>
<td>
<asp:RegularExpressionValidator id="RegularExpressionValidator1" runat ="server"
ErrorMessage="Please give Email Address! "
ControlToValidate="txt_address"
ValidationExpression="\S+#\S+\.\S+\w+"//example (example#yahoo.com)
ForeColor="Red" >
</asp:RegularExpressionValidator>
</td>
</tr>
</table>
<table>
<tr>
<td>
<asp:RadioButtonList ID="rbl_gender" runat="server">
<asp:ListItem>Male</asp:ListItem>
<asp:ListItem>Female</asp:ListItem>
</asp:RadioButtonList>
</td>
<td>
<asp:RequiredFieldValidator ID="RequiredFieldVlidator2" runat="server"
ErrorMessage="Please Choose your Gender" ControlToValidate="rbl_gender"
ForeColor="Red" >
</asp:RequiredFieldValidator>
</td>
</tr>
</table>
<table>
<tr>
<td>
<asp:RequiredFieldValidator ID="RequiredFeildValidator1"
runat ="server" ControlToValidate ="txt_name"
ErrorMessage="Please Insert Your name !"
ForeColor="Red">
</asp:RequiredFieldValidator>
</td>
</tr>

Answer 4

A very small change in the ValidationExpression seems to make the difference between only sometimes working, and reliably working.
The following worked for me in development, but not in production:
<asp:RegularExpressionValidator Display = "Dynamic" ControlToValidate = "tbCarePlan" ID="revCarePlan" ValidationExpression = "^(.{0,4000})$" runat="server" ErrorMessage="Max 4000 characters allowed." />
Replacing the ValidationExpression above with "[\s\S]{0,4000}" it now works reliably. Leave out the ^ and $ - the RegularExpressionValidator does not require this.