Checking for a Range of Values: The RangeValidator Control

Checking for a Range of Values: The `RangeValidator` Control

You can use the RangeValidator control to check whether the value of a form field falls between a minimum and maximum value. The minimum and maximum values can be dates, numbers , currency amounts, or strings. All the properties and methods of this control are listed in Table 3.4.

Table 3.4. `RangeValidator` Properties, Methods, and Events

Properties	Description
`ControlToValidate`	Specifies the ID of the control that you want to validate.
`Display`	Sets how the error message contained in the `Text` property is displayed. Possible values are `Static` , `Dynamic` , and `None` ; the default value is `Static` .
`EnableClientScript`	Enables or disables client-side form validation. This property has the value `True` by default.
`Enabled`	Enables or disables both server and client-side validation. This property has the value `True` by default.
`ErrorMessage`	Specifies the error message that is displayed in the `ValidationSummary` control. This error message is displayed by the control when the `Text` property is not set.
`IsValid`	Has the value `True` when the validation check succeeds and `False` otherwise .
`MaximumValue`	Specifies the maximum value in the range of permissible values.
`MinimumValue`	Specifies the minimum value in the range of values.
`Text`	Sets the error message displayed by the control.
`Type`	Gets or sets the data type to use when comparing values. Possible values are `Currency` , `Date` , `Double` , `Integer` , and `String` .
Methods	Description
`Validate`	Performs validation and updates the `IsValid` property.
Events	Description
None

You can use RangeValidator , for example, to check whether a form field contains a date that falls within a certain range. The page in Listing 3.15 checks whether the date entered is greater or equal to today's date, but less than three months in the future.

Listing 3.15 `RangeValidator.aspx`

 <Script Runat="Server"> Sub Page_Load   valgMeetingDate.MinimumValue = Now.Date   valgMeetingDate.MaximumValue = Now.Date.AddMonths( 3 ) End Sub Sub Button_Click( s As Object, e As EventArgs )   If IsValid Then     Response.Redirect( "ThankYou.aspx" )   End If End Sub </Script> <html> <head><title>RangeValidator.aspx</title></head> <body> <form Runat="Server"> Choose a meeting date in the next three months: <br> <asp:TextBox   id="txtMeetingDate"   Columns="10"   Runat="Server"/> <asp:RangeValidator   ID="valgMeetingDate"   ControlToValidate="txtMeetingDate"   Display="Dynamic"   Text="Date must be in the next 3 months!"   Type="Date"   Runat="Server" /> <p> <asp:Button   Text="Submit"   OnClick="Button_Click"   Runat="Server"/> </form> </body> </html>

The C# version of this code can be found on the CD-ROM.

The Page_Load subroutine in Listing 3.15 assigns values to the MinimumValue and MaximumValue properties of the RangeValidator control. Today's date is assigned to the MinimumValue property, and a date three months in the future is assigned to the MaximumValue property.

If you need to detect whether a value entered into a form field falls within a certain range determined by the values of other form fields, you should use the CompareValidator rather than the RangeValidator . The CompareValidator , unlike RangeValidator , enables you to compare the values of different controls.

For example, the page in Listing 3.16 contains three TextBox controls. You must enter a number greater than or equal to the value entered into the first control, and less than or equal to the value entered into the last control; otherwise, you receive an error.

Listing 3.16 `CompareValidatorRange.aspx`

 <Script Runat="Server"> Sub Button_Click( s As Object, e As EventArgs )   If IsValid Then     Response.Redirect( "Thankyou.aspx" )   End If End Sub </Script> <html> <head><title>CompareValidatorRange.aspx</title></head> <body> <form Runat="Server"> Minimum Value: <asp:TextBox   id="txtMinNumber"   Runat="Server"/> <p> Maximum Value: <asp:TextBox   id="txtMaxNumber"   Runat="Server"/> <p> Value: <asp:TextBox   id="txtRangeNumber"   Runat="Server"/> <asp:CompareValidator   ControlToValidate="txtRangeNumber"   ControlToCompare="txtMinNumber"   Display="Dynamic"   Text="Number must be greater than minimum value!"   Operator="GreaterThan"   Type="Integer"   Runat="Server" /> <asp:CompareValidator   ControlToValidate="txtRangeNumber"   ControlToCompare="txtMaxNumber"   Display="Dynamic"   Text="Number must be less than maximum value!"   Operator="LessThan"   Type="Integer"   Runat="Server" /> <p> <asp:Button   Text="Submit"   OnClick="Button_Click"   Runat="Server"/> </form> </body> </html>

The C# version of this code can be found on the CD-ROM.

Checking for a Range of Values: The RangeValidator Control