Checking a Range


ASP.NET Developer's JumpStart
By Paul D. Sheriff, Ken Getz
Table of Contents
Chapter 8.  Validation Controls

The RangeValidator control allows you to verify that the value of a control falls within a specified range. For example, you could make sure that a text box's value is between 5 and 10 or between a month ago and the current date.

Normally, you'll need to set the properties shown in Table 8.3, in addition to those listed in Table 8.1.

Table 8.3. Set These Properties for RangeValidator Controls
Property Description
MaximumValue The maximum allowable value.
MinimumValue The minimum allowable value.
Type The type of data to compare, selected from String, Integer, Date, Double, or Currency. This property controls the type of comparison to perform it wouldn't make sense to perform a text comparison when you're entering numeric values, for example. If you did, "2" would be greater than "11." Select the correct data type to perform the correct type of comparison.


In order to try out this control, you will modify the sample page, EmpMaint.aspx, adding a RangeValidator control to ensure that the employee birth date falls between 1/1/1900 and 12/31/1984. Here are the steps to follow:

  1. Click to the right of the RequiredFieldValidator control that's associated with the BirthDate field, moving the selection point to that location.

  2. In the Toolbox, double-click the RangeValidator control to add it adjacent to the existing RequiredFieldValidator control.

  3. Set the properties for the control as shown in Table 8.4.

    Table 8.4. Set These Properties for the RangeValidation Control
    Property Value
    ID rvalBirthdate
    ControlToValidate txtBirthDate
    ErrorMessage Birth Date must be between 1/1/1900 and 12/31/1984
    MaximumValue 12/31/1984
    MinimumValue 1/1/1900
    Type Date

  4. Right-click the page and select Build and Browse from the context menu.

  5. Enter an invalid date for the Birth Date field (perhaps a date after 12/31/1984) and then press Tab to leave the control. You should see an error appear immediately.

  6. Close the browser window.


Although we've used dates formatted correctly for the United States here, you'll need to take into account the current locale when testing your pages. If your date format is different from ours, make sure you attempt to validate dates that are correct for the locale of the browser.

Although you did see the correct error message, you may have noticed that it didn't appear immediately to the right of the associated text box. Because you had already placed another validation control adjacent to the Birth Date text box, that control "consumes" the space where you'd expect to see the out-of-range error message.

To solve this problem, you can use the Display property of the validation controls. This property has three values: None, Dynamic, and Static. The default value is Static, indicating that the control always takes up the same amount of space on the rendered page. Selecting None causes the control to take up no space and never display any text (unless you add a ValidationSummary control to the page). Selecting Dynamic allows the control to take up no space if it isn't displaying any text. This choice, then, will fix the problem. Simply follow these steps:

  1. Select each of the validation controls on the page and set the Display property for each to Dynamic.

  2. Repeat the previous experiment and prove to yourself that the display works better now.


If you only want to validate that the user has entered a particular data type (a date, for example) but don't care about the specific value, you can use the CompareValidator control, discussed later in the chapter.

  1. If you want to provide a dynamic range for the RangeValidator control (for example, allowing dates to be entered for the Birth Date field between 70 years ago and 17 years ago, figuring that you can't hire anyone older than 70 or younger than 17), you'll need to write a little code. You might want to modify the EmpMaint.aspx page so that it adds these restrictions as it loads.

  2. Modify the Page_Load procedure of EmpMaint.aspx so that it looks like this:

     Private Sub Page_Load( _  ByVal sender As System.Object, _  ByVal e As System.EventArgs) Handles MyBase.Load   If Not Page.IsPostBack Then     With rvalBirthDate       .MinimumValue = CStr(Today.AddYears(-70))       .MaximumValue = CStr(Today.AddYears(-17))       .ErrorMessage = String.Format( _        "Enter a date between {0} and {1}", _        .MinimumValue, .MaximumValue)     End With   End If End Sub 
  3. Browse the page again and try entering a birth date that's more than 70 years ago or less than 17 years ago. You'll see the error message, indicating the valid range of dates.

The previous example brings up some interesting ideas:

  • You can use the AddYears method of a date to add or subtract years.

  • The MinimumValue and MaximumValue properties of the RangeValidator control both accept String values you'll need to convert anything you place in these properties into strings.

  • You can dynamically modify the ErrorMessage text of a control.


    ASP. NET Developer's JumpStart
    ASP.NET Developers JumpStart
    ISBN: 0672323575
    EAN: 2147483647
    Year: 2002
    Pages: 234 © 2008-2017.
    If you may any questions please contact us: