You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. You write the following code segment. (Line numbers are included for reference only.) the TextBox control is data-bound to an instance of the Contact class. You need to ensure that the Contact class contains a business rule to ensure that the ContactName property is not empty or NULL. You also need to ensure that the TextBox control validates the input data. Which two actions should you perform?（）