Often a simple value or range check is
insufficient; you must check that the form of
the data entered is correct. For example, you may need to ensure that
a zip code is five digits, an email address is in the form
[email protected], a credit card matches the right
format, and so forth.
A regular expression validator allows you to validate that a text
field matches a regular expression. Regular
expressions are a language for describing and manipulating text. For
more complete coverage of this topic, please see MasteringRegularExpressions
by
Jeffrey Friedl (O’Reilly).
A regular expression consists of two types of characters:
literals
and
metacharacters
. A literal is just a
character you wish to match in the target string. A metacharacter is
a special symbol that acts as a command to the regular expression
parser. The parser is the engine responsible for understanding the
regular expression. Consider this regular expression:
^d{5}$This will match any string that has exactly 5 numerals. The initial
metacharacter, ^, indicates the beginning of the
string. The second metacharacter, d, indicates a
digit. The third metacharacter, {5}, indicates
exactly 5 of the digits, and the final metacharacter,
$, indicates the end of the string. Thus, this
regular expression matches five digits between the beginning and end
of the line, and nothing else.
Note
A slightly more sophisticated algorithm might accept either a 5 digit
zip code or a 9 digit (plus 4) zip code in the format of 12345-1234.
Rather than using the d metacharacter, you could
simply designate the range of acceptable values:
ValidationExpression="[0-9]{5}|[0-9]{5}-{0-9]{4}"You create a RegularExpressionValidator much as you did the previous
validators. The only new attribute is
ValidationExpression
,
which takes a valid regular expression within quotes. For example,
the following code fragment defines a regular expression validator to
insure that the value entered into a text box is a five digit numeric
zip code:
<asp:RegularExpressionValidator ID="regExVal"
ControlToValidate="txtZip" Runat="server"
ValidationExpression="^d{5}$"
display="Static">Please enter a valid 5 digit Zip code</asp:RegularExpressionValidator>If the control pointed to by
ControlToValidate
has a string that matches the regular
expression, validation succeeds. The complete source is shown in
Example 8-5.
Example 8-5. Regular expression validator
<%@ Page language="c#" Codebehind="WebForm1.aspx.cs" AutoEventWireup="false"
Inherits="RegularExpressionValidation.WebForm1" %>
<HTML>
<HEAD>
<meta content="Internet Explorer 5.0" name=vs_targetSchema>
<meta content="Microsoft Visual Studio 7.0" name=GENERATOR>
<meta content=C# name=CODE_LANGUAGE>
</HEAD>
<body MS_POSITIONING="GridLayout">
<form method=post runat="server">
<table>
<tr>
<td colspan="2">
<h5>Please enter your Zip Code</h5>
</td>
</tr>
<tr>
<td>
<asp:TextBox width="60" ID="txtZip" runat="server" />
</td>
<td>
<asp:RegularExpressionValidator ID="regExVal"
ControlToValidate="txtZip" Runat="server"
ValidationExpression="^d{5}$"
display="Static">Please enter a valid 5 digit Zip
code</asp:RegularExpressionValidator>
</td>
</tr>
<tr>
<td>
<asp:Button ID="btnValidate" Text="Validate"
Runat="server"></asp:Button>
</td>
<td>
<asp:Label ID="lblMsg" Runat="server" Text=""/>
</td>
</tr>
</table></FORM>
</body>
</HTML>