Build Your Own ASP.NET 3.5 Website Using C# & VB (44 page)

If you’re working with Visual Web Developer, you can see the validation controls

in the
Validation
tab of the Toolbox, as
Figure 6.4 illustrates.

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Using the Validation Controls

239

Figure 6.4. Accessing the validation controls in Visual Web Developer

Validation controls, like other web server controls, are inserted as tags with the

asp: prefix. Once a validation control is inserted, it validates an existing control

elsewhere on the page, and presents an error message to the user if necessary. To

validate a field, all you have to do is insert a control—there’s no JavaScript or clumsy

server-side code to write by hand! Let’s take a look at these ASP.NET validation

controls in detail now.

RequiredFieldValidator

The RequiredFieldValidator control is the simplest of the validation controls. It

does exactly what its name suggests: it makes sure that a user enters a value into a

web control. We used the RequiredFieldValidator control in the login page example presented earlier:
LearningASP\VB\Login_06.aspx
(excerpt)

ControlToValidate="passwordTextBox"

ErrorMessage="Password is required!"

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

The ControlToValidate property contains the ID of the web control that the

RequiredFieldValidator control is assigned to. The ErrorMessage property contains

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

the error message that will be displayed when the user fails to enter a value into

each control.

CompareValidator

One of the most useful validation controls is the CompareValidator control, which

performs a comparison between the data entered into a given control and some

other value. That other value can be a fixed value, such as a number, or a value

entered into another control.

Let’s look at an example that builds on the login example we saw in the previous

section. Here, we’ll validate that the data entered into both the password fields is

identical. Make the following changes to
Login.aspx
:

LearningASP\VB\Login_07.aspx
(excerpt)

Password and Confirmation:

⋮

ControlToCompare="passwordTextBox"

ControlToValidate="confirmPasswordTextBox"

ErrorMessage="Your passwords do not match up!"

Display="Dynamic" />

Run the page and enter a different password into each field. The
CompareValidator

control will appear as soon as you move on from the two fields whose data doesn’t

match, as
Figure 6.5 shows.

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Using the Validation Controls

241

Figure 6.5. A CompareValidator control in action

As you’ve probably noticed, the CompareValidator control differs very little from

the RequiredFieldValidator control:

LearningASP\VB\Login_07.aspx
(excerpt)

runat="server" ControlToValidate="confirmPasswordTextBox"

ErrorMessage="Password confirmation is required!"

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

ControlToCompare="passwordTextBox"

ControlToValidate="confirmPasswordTextBox"

ErrorMessage="Your passwords do not match up!"

Display="Dynamic" />

The only difference is that in addition to a ControlToValidate property, the

CompareValidator has a ControlToCompare property. We set these two properties

to the IDs of the controls we want to compare. So, in our example, the

ControlToValidate property is set to the confirmPasswordTextBox, and the

ControlToCompare property is set to the passwordTextBox.

The CompareValidator can be used to compare the value of a control to a fixed

value, too. CompareValidator can check whether the entered value is equal to, less

than, or greater than any given value. As an example, let’s add an “age” field to our

login form:

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LearningASP\VB\Login_08.aspx
(excerpt)

Age:

ControlToValidate="ageTextBox"

ErrorMessage="Age is required!"

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

Operator="GreaterThan" Type="Integer"

ControlToValidate="ageTextBox" ValueToCompare="15"

ErrorMessage="You must be 16 years or older to log in" />

In this case, the CompareValidator control is used to check that the user is old

enough to log in to our fictitious web application. Here, we set the Operator property

of the CompareValidator to GreaterThan. This property can take on any of the

values Equal, NotEqual, GreaterThan, GreaterThanEqual, LessThan, LessThanEqual,

or DataTypeCheck, which we’ll look at shortly. Next, we tell the CompareValidator

control to compare the two values by setting the Type property to Integer, which

will cause the CompareValidator to treat the values as whole numbers (this property

can also be set to Currency or Date, among other options). Finally, we use the

ValueToCompare property to make sure that the user’s age is greater than 15. If you

load this page in your web browser now, you’ll see that the form is only validated

when the user enters an age of 16 or more.

We can also use the CompareValidator control to perform data type checks. To see

how this works, let’s replace the age TextBox control with a date-of-birth text box,

whose value must be a valid date:

LearningASP\VB\Login_09.aspx
(excerpt)

Birth Date:

Operator="DataTypeCheck" Type="Date"

ControlToValidate="birthDateTextBox"

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Using the Validation Controls

243

ErrorMessage="You must enter the date in a valid format!"

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

As you can see, the Operator property of the CompareValidator control is set to

perform a DataTypeCheck, and the Type property is set to Date. Load the page, and

you’ll see that you can’t enter anything other than a valid date into this field. The

constituents of a “valid” date will depend on the regional settings on your web

server.

RangeValidator

The RangeValidator control checks whether the value of a form field falls between

minimum and maximum values. For instance, we could make sure that users who

visit our web site were born in a certain decade. If they enter values that don’t fit

into the range we specify, the validator will return an “invalid” message.

Let’s continue by expanding
Login.aspx
even further:

LearningASP\VB\Login_10.aspx
(excerpt)

Birth Date:

Type="Date" ControlToValidate="birthDateTextBox"

MinimumValue="1/1/1970" MaximumValue="12/31/1979"

ErrorMessage="You must've been born in the 1970s to use

this web site!" />

Take Care when Specifying Dates

If you’re located outside of the US, you may need to modify the above example.

In the US, dates are specified in month-day-year format. In the UK and Australia,

they’re specified in day-month-year order, and in other countries, the year is

specified first. The ASP.NET runtime will be expecting you to specify dates in

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

your local format, so adjust the values of the MinimumValue and MaximumValue

properties accordingly.

Here, we’ve added a RangeValidator to validate the birthDateTextBox control.

Our RangeValidator control checks whether the date entered falls within the 1970s,

and shows an error message similar to
Figure 6.6 if it doesn
’t.

Figure 6.6. Using the RangeValidator control