Evjen c04.tex V2 - 01/28/2008 12:45pm Page 204
Chapter 4: Validation Server Controls
associates itself with one of the form elements on the page. In this case, you need only a single
CompareValidator control on the page because a single comparison is made. In this example, you are
making a comparison between the value of
TextBox2
and that of
TextBox1
. Therefore, you use the
ControlToCompare
property. This specifies what value is compared to
TextBox2
. In this case, the value
is
TextBox1
.
It’s as simple as that. If the two text boxes do not match after the page is posted by the end user, the value
of the
Text
property from the CompareValidator control is displayed in the browser. An example of this
is shown in Figure 4-2.
Figure 4-2
Validating Against Constants
Besides being able to validate values against values in other controls, you can also use the Compare
Validator control to make comparisons against constants of specific data types. For example, suppose
you have a text box on your registration form that asks for the age of the user. In most cases, you want to
get back an actual number and not something such as
aa
or
bb
as a value. Listing 4-9 shows you how

Type
property can take the following values:
❑
Currency
❑
Date
❑
Double
❑
Integer
❑
String
Not only can you make sure that what is entered is of a specific data type, but you can also make sure
that what is entered is valid when compared to specific constants. For instance, you can make sure what
is entered in a form element is greater than, less than, equal to, greater than or equal to, or less than or
equal to a specified value. An example of this is illustrated in Listing 4-10.
Listing 4-10: Making comparisons with the CompareValidator control
Age:
<
asp:TextBox ID="TextBox1" Runat="server"
><
/asp:TextBox
>
&nbsp;
<
asp:CompareValidator ID="CompareValidator1" Runat="server"
Operator="GreaterThan" ValueToCompare="18"
ControlToValidate="TextBox1"
Text="You must be older than 18 to join" Type="Integer"
>

205
Evjen c04.tex V2 - 01/28/2008 12:45pm Page 206
Chapter 4: Validation Server Controls
The
ValueToCompare
property is where you place the constant value used in the comparison. In the
preceding example, it is the number
18
.
The RangeValidator Server Control
The RangeValidator control is quite similar to that of the CompareValidator control, but it makes sure
that the end-user value or selection provided is between a specified range as opposed to being just greater
than or less than a specified constant. For an example of this, go back to the text-box element that asks for
the age of the end user and performs a validation on the value provided. This is illustrated in Listing 4-11.
Listing 4-11: Using the RangeValidator control to test an integer value
Age:
<
asp:TextBox ID="TextBox1" Runat="server"
><
/asp:TextBox
>
&nbsp;
<
asp:RangeValidator ID="RangeValidator1" Runat="server"
ControlToValidate="TextBox1" Type="Integer"
Text="You must be between 30 and 40"
MaximumValue="40" MinimumValue="30"
><
/asp:RangeValidator
>

arrival date needs to be within two weeks of the current date. You can use the RangeValidator control to
test for these scenarios quite easily.
Because the date range that you want to check is dynamically generated, you assign the
MaximumValue
and
MinimumValue
attribute programmatically in the
Page_Load
event. In the Designer, your sample page
for this example should look like Figure 4-4.
Figure 4-4
207
Evjen c04.tex V2 - 01/28/2008 12:45pm Page 208
Chapter 4: Validation Server Controls
The idea is that the end user will select a date from the Calendar control, which will then populate the
TextBox control. Then, when the end user clicks the form’s button, he is notified if the date selected is
invalid. If the date selected is valid, that date is presented through the Label control on the page. The
code for this example is presented in Listing 4-12.
Listing 4-12: Using the RangeValidator control to test a string date value
VB
<
%@ Page Language="VB" %
>
<
script runat="server"
>
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
RangeValidator1.MinimumValue = DateTime.Now.ToShortDateString()
RangeValidator1.MaximumValue = DateTime.Now.AddDays(14).ToShortDateString()
End Sub

>
<
form id="form1" runat="server"
>
Arrival Date:
<
asp:TextBox ID="TextBox1" runat="server"
><
/asp:TextBox
>
&nbsp;
<
asp:RangeValidator ID="RangeValidator1" runat="server"
Text="You must only select a date within the next two weeks."
ControlToValidate="TextBox1" Type="Date"
><
/asp:RangeValidator
><
br /
>
<
br /
>
Select your arrival date:
<
br /
>
<
asp:Calendar ID="Calendar1" runat="server"
OnSelectionChanged="Calendar1_SelectionChanged"

>
<
/html
>
C#
<
%@ Page Language="C#" %
>
<
script runat="server"
>
protected void Page_Load(object sender, EventArgs e)
{
RangeValidator1.MinimumValue = DateTime.Now.ToShortDateString();
RangeValidator1.MaximumValue =
DateTime.Now.AddDays(14).ToShortDateString();
}
protected void Calendar1_SelectionChanged(object sender, EventArgs e)
{
TextBox1.Text = Calendar1.SelectedDate.ToShortDateString();
}
protected void Button1_Click(object sender, EventArgs e)
{
if (Page.IsValid)
{
Label1.Text = "You are set to arrive on: " + TextBox1.Text.ToString();
}
}
<
/script

matches the one that you define. For instance, you can define that the structure of the user input must
be in the form of an e-mail address or an Internet URL;ifitdoesn’tmatchthisdefinition,thepageis
considered invalid. Listing 4-13 shows you how to validate what is input into a text box by making sure
it is in the form of an e-mail address.
209
Evjen c04.tex V2 - 01/28/2008 12:45pm Page 210
Chapter 4: Validation Server Controls
Figure 4-5
Listing 4-13: Making sure the text-box value is an e-mail address
Email:
<
asp:TextBox ID="TextBox1" Runat="server"
><
/asp:TextBox
>
&nbsp;
<
asp:RegularExpressionValidator ID="RegularExpressionValidator1"
Runat="server" ControlToValidate="TextBox1"
Text="You must enter an email address"
ValidationExpression="
\
w+([-+.]
\
w+)*@
\
w+([ ]
\
w+)*
\

to the
ValidationExpression
property to launch the Regular Expression Editor. This editor is shown in
Figure 4-6.
Figure 4-6
Using this editor, you can find regular expressions for things like e-mail addresses, Internet URLs, zip
codes, phone numbers, and social security numbers. In addition to working with the Regular Expression
Editor to help you with these sometimes complicated regular expression strings, you can also find a
good-sized collection of them at an Internet site called RegExLib found at
www.regexlib.com
.
The CustomValidator Server Control
So far, you have seen a wide variety of validation controls that are at your disposal. In many cases, these
validation controls address many of the validation rules that you want to apply to your Web forms.
Sometimes, however, none of these controls works for you, and you have to go beyond what they offer.
This is where the CustomValidator control comes into play.
The CustomValidator control allows you to build your own client-side or server-side validations that can
then be easily applied to your Web forms. Doing so allows you to make validation checks against values
or calculations performed in the data tier (for example, in a database), or to make sure that the user’s
input validates against some arithmetic validation (for example, determining if a number is even or odd).
You can do quite a bit with the CustomValidator control.
Using Client-Side Validation
One of the worthwhile functions of the CustomValidator control is its capability to easily provide custom
client-side validations. Many developers have their own collections of JavaScript functions they employ
in their applications, and using the CustomValidator control is one easy way of getting these functions
implemented.
211
Evjen c04.tex V2 - 01/28/2008 12:45pm Page 212
Chapter 4: Validation Server Controls
For example, look at a simple form that asks for a number from the end user. This form uses the

>
function validateNumber(oSrc, args) {
args.IsValid = (args.Value % 5 == 0);
}
<
/script
>
<
/head
>
<
body
>
<
form id="form1" runat="server"
>
<
div
>
<
p
>
Number:
<
asp:TextBox ID="TextBox1"
Runat="server"
><
/asp:TextBox
>
&nbsp;

/asp:Label
>
<
/p
>
<
/div
>
<
/form
>
<
/body
>
<
/html
>
212
Evjen c04.tex V2 - 01/28/2008 12:45pm Page 213
Chapter 4: Validation Server Controls
C#
<
%@ Page Language="C#" %
>
<
script runat="server"
>
protected void Button1_Click(Object sender, EventArgs e) {
Label1.Text = "VALID NUMBER!";
}

<
/script
>
This second <
script
> section is the client-side JavaScript that you want the CustomValidator control
to use when making its validation checks on the information entered into the text box. The JavaScript
functions you employ are going to use the
args.IsValid
property and set this property to either
true
or
false
depending on the outcome of the validation check. In this case, the user input (
args.Value
)is
checked to see if it is divisible by
5
. The Boolean value returned is then assigned to the
args.IsValid
property, which is then used by the CustomValidator control.
The CustomValidator control, like the other controls before it, uses the
ControlToValidate
property
to associate itself with a particular element on the page. The property that you are interested in here is
the
ClientValidationFunction
property. The string value provided to this property is the name of the
client-side function that you want this validation check to employ when the CustomValidator control is
triggered. In this case, it is