Build Your Own ASP.NET 3.5 Website Using C# & VB (45 page)

Note that the Type property of the RangeValidator control specifies the data type

that’s expected in the control with which it’s associated; if some other data type is

entered into this field, it fails validation. As such, we’ve removed the

CompareValidator we added for this purpose.

ValidationSummary

Imagine we have a form that contains many form fields. If that page contains errors,

it could be difficult for users to figure out which control caused a given error, because

the page is so big. The ValidationSummary control can alleviate this problem by

presenting the user with a list of error messages in one place on the page. Let’s see

the ValidationSummary control in use. Add it to the end of your
Login.aspx
file, like

so:

LearningASP\VB\Login_11.aspx
(excerpt)

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Using the Validation Controls

245

When the user clicks the
Submit
button, the ValidationSummary is populated

automatically with a list of all the errors on the page, as we can see in Figure 6.7
. Figure 6.7. Using the ValidationSummary control

This control isn’t particularly good looking, but you can see its potential. If you set

the Display properties of all the other validation controls on the page to None, you

could use a ValidationSummary to show all the errors in one place.

If you set the ShowMessageBox property of the ValidationSummary control to True,

the list of errors will be shown in a JavaScript alert
box similar to Figure 6.8
. The server-side list will still be shown to users who don’t have JavaScript-enabled

browsers.

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

Figure 6.8. Showing validation errors in a dialog

RegularExpressionValidator

The RegularExpressionValidator lets you specify a regular expression that describes all the allowable values for a field. Regular expressions are powerful tools for manipulating strings, and are supported by many programming languages.

They’re commonly used to check for patterns inside strings. Consider, for instance,

the following regular expression:

^\S+@\S+\.\S+$

In plain English, this expression will match any string that begins with one or more

non-whitespace characters followed by the @ character, then one or more nonwhitespace characters, then a dot (.), then one or more non-whitespace characters, followed by the end of the string.

This regular expression describes any one of these email addresses:

■ [email protected]

■ [email protected]

■ [email protected]

However, the regular expression would fail if the user typed in one of these entries:

■ books@sitepoint

■ joe [email protected]

Although regular expressions cannot check to see if the email address itself is valid,

they can, at the very least, provide a means for us to determine whether or not the

user has entered a string of characters that has all the key components of a valid

email address.

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Using the Validation Controls

247

Let’s change the username field in our login form to an email address field, and

validate it using the RegularExpressionValidator control.

LearningASP\VB\Login_12.aspx
(excerpt)

Email address:

ControlToValidate="emailTextBox"

ErrorMessage="Email address is required!"

SetFocusOnError="True" Display="Dynamic" />

runat="server" ControlToValidate="emailTextBox"

ValidationExpression="^\S+@\S+\.\S+$"

ErrorMessage="You must enter a valid email address!" />

The important property within this control is ValidationExpression, to which we

assign the regular expression that’s appropriate for handling our custom validation

functionality
. Figure 6.9
shows the error message that appears when a user enters an incorrect email address.

Figure 6.9. Using the RegularExpressionValidator control

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

Some Useful Regular Expressions

Writing regular expressions can be tricky, and a comprehensive discussion of the

topic is outside the scope of this book. Many of the regular expressions presented

here are nowhere near as rigorous as they could be, but they’re still quite useful.

The book
Mastering Regular Expressions
, by Jeffrey E. F. Friedl, contains a single

expression for checking email addresses that tops 6,000 characters!1

Table 6.1
outlines the usage of some simple regular expressions.
Table 6.1. Some simple regular expressions

Description

Regular Expression

email address

^\S+@\S+\.\S+$

web URL

^https?://\S+\.\S+$

US phone numbers ((
555
)
555
-
5555
or

^\(?\d{3}\)?(\s|-)\d{3}-\d{4}$

555
-
555
-
5555
)

international phone numbers (begins with a digit,

^\d(\d|-){7,20}$

followed by between seven and 20 digits and/or

dashes)

five-digit ZIP code

^\d{5}$

nine-digit ZIP code

^\d{5}-\d{4}$

either five-digit or nine-digit ZIP code

^(\d{5})|(\d{5}\-\d{4})$

US social security number

^\d{3}-\d{2}-\d{4}$

Take a close look at the components of the regular expressions in
Table 6.2, and

you should begin to see how they work. If you’d like more information on regular

expressions, try the following resources:

Regular Expression Library
2

a searchable library of regular expressions

Using Regular Expressions in PHP
3

a great article on the use of regular expressions and PHP

1 Jeffrey E. F. Friedl,
Mastering Regular Expressions
, Third Edition (Sebastopol: O’Reilly Media), 2006. 2 http://www.regexlib.com/

3 http://www.sitepoint.com/article/regular-expressions-php

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Using the Validation Controls

249

Regular Expressions in JavaScript
4

another great article, this time on the use of regular expressions with JavaScript

Table 6.2. Common regular expression components and their descriptions

Special Character

Description

.

any character

^

beginning of string

$

end of string

\d

numeric digit

\s

whitespace character

\S

non-whitespace character

(abc)

the string abc as a group of characters

?

preceding character or group is optional

+

one or more of the preceding character or group

*

zero or more of the preceding character or group

{
n
}

exactly
n
of the preceding character or group

{
n
,
m
}

n
to
m
of the preceding character or group

(
a
|
b
)

either
a
or
b

\$

a dollar sign (as opposed to the end of a string). We can
escape
any of the

special characters listed above by preceding it with a backslash. For example,

\. matches a period character, \? matches a question mark, and so on.

You’ll find a complete guide and reference to regular expressions and their components in the .NET Framework SDK Documentation.
CustomValidator

The validation controls included with ASP.NET allow you to handle many kinds

of validation, yet certain types of validation cannot be performed with these builtin controls. For instance, imagine that you needed to ensure that a new user’s login details were unique by checking them against a list of existing usernames on the

server. The CustomValidator control can be helpful in this situation, and others

like it. Let’s see how:

4 http://www.sitepoint.com/article/expressions-javascript

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

Visual Basic

LearningASP\VB\CustomValidator.aspx
(excerpt)

<%@ Page Language="VB" %>

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

C#

LearningASP\CS\CustomValidator.aspx
(excerpt)