Build Your Own ASP.NET 2.0 Web Site Using C# & VB, Second Edition

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:

File: Login.aspx (excerpt)

<!-- Birth Date -->

<p>

Birth Date:<br />

<asp:TextBox id="birthDateTextBox" runat="server" />

<asp:CompareValidator id="birthDateCheck" runat="server"

Operator="DataTypeCheck" Type="Date"

ControlToValidate="birthDateTextBox"

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

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

</p>

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:

File: Login.aspx (excerpt)

<!-- Birth Date -->

<p>

Birth Date:<br />

233

RangeValidator

<asp:TextBox id="birthDateTextBox" runat="server" />

<asp:RangeValidator id="birthDateRangeTest" runat="server"

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!" />

</p>

Take Care when Specifying Dates

If you’re 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 Aus-

tralia, 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 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

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.

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Chapter 6: Using the Validation Controls