Summary

This chapter began by defining the two types of input validation: syntactic and semantic. Syntactic validation ensures that user input has the correct format and can be converted to the correct type, whereas semantic validation may entail more complex validation, such as the evaluation of business rules.

This chapter then looked at the Silverlight 3 property setter validation system, which is included in the Windows Phone SDK. You saw how this system relies on the raising of exceptions to indicate validation errors. Noncritical exceptions raised in property setters produce binding errors, which signal validation errors.

You saw how Windows Phone requires custom templates for enabling visualization of input validation errors, and you looked at using Expression Blend to copy and customize the way error-related visual states are displayed.

Finally, the chapter examined the Silverlight 4 validation system, which is also included in the Windows Phone SDK, and which enables asynchronous and composite input validation. You looked at setting control-enabled states based on the presence of validation errors, and at hiding validation errors until the user has had a chance to fill out the form.