- Chapter 3: Performing Form Validation with Validation Controls
- Requiring Fields: The RequiredFieldValidator Control
- Validating Expressions: The RegularExpressionValidator Control
- Comparing Values: The CompareValidator Control
- Checking for a Range of Values: The RangeValidator Control
- Summarizing Errors: The ValidationSummary Control
- Performing Custom Validation: The CustomValidator Control
- Disabling Validation
- Summary
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 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>