In a perfect world, every user that uses our forms would enter the exact right data at the right places. In such a world, data validation would be useless. We aren't living in such world, and so data validation is a concept no form can go without. Whenever you are interacting with the user, you want to make sure that he inputs what you expect him to input and nothing else. Silverlight 4 introduced two new interfaces for validation—IDataErrorInfo and INotifyDataErrorInfo. These two interfaces join the other approach of data validation in Silverlight known as the data binding exception approach, which includes the NotifyOnValidationError, ValidatesOnExceptions, ValidatesOnDataErrors, and ValidatesOnNotifyDataErrors objects.

Throughout this topic, we are going to work with a sole project—Chapter5-DataValidation. The project contains a simple grid with a few text boxes that we will validate using the various data validation approaches in Silverlight. If you build...