I have a RadioButton inside ItemsControl. By default Radio Buttons will be unchecked. I want the user to select either of the radio buttons if a partic
ValidationRules can be added as an extension of the Binding property, like so:
(Note for the above that you don't actually need to use a TextBlock if all you're doing is putting text in the block. You can just include that text binding in the Content="" field on the RadioButton.)
Then you'd also need to define an object (YourValidationRule) that inherits from ValidationRule and overrides public ValidationResult Validate(object value, CultureInfo cultureInfo), and add a static reference (rules, in this case) to the namespace in which your custom ValidationRule exists.
An in-depth tutorial for ValidationRules exists on MSDN at this link: http://msdn.microsoft.com/en-us/library/ms753962%28v=vs.110%29.aspx
However, Miiko is correct - it may be easier for you to use an object that implements ICommand, and use CanExecute to determine whether the customer may proceed. The main downside of this is that a ghosted, unusable button is not necessarily communicative, and you should be careful to ensure that your customers understand why they're unable to use the button.