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How to: Validate Against a Data Type for ASP.NET Server Controls
You can validate a user's entry in an ASP.NET Web page against a specific data type to be sure that what the user has entered is a number, or a date, and so on. For example, if you want to collect birth date information on a user registration page, you can use a CompareValidator control to make sure that the date is in a recognized format before it is submitted.
To validate against a data type
Add a CompareValidator control to the page and set the following properties:
The ID of the control for which you are checking the data type.
Properties that specify the text and location of the error or errors that will display if the validation fails. For details, see How to: Control Validation Error Message Display for ASP.NET Server Controls.
Set the data type to compare to by setting the following properties:
If the user leaves a control blank, the control passes the comparison validation. To force the user to enter a value, add a RequiredFieldValidator control as well. For details, see How to: Validate Required Entries for ASP.NET Server Controls.
Add a test in your ASP.NET Web page code to check for validity. For details, see How to: Test Validity Programmatically for ASP.NET Server Controls.