Field Validation in windows phone 8.1 universal app - xaml

Question

In windows phone 8 we used System.ComponentModel.DataAnnotations to validate input in ViewModel and show validation error message in control tooltip. What is the equivalent way and best practice for validating input in windows phone 8.1 Universal app?

Answer 1

Since Windows 8.1 universal apps do not support Data Annotations, you can't use the [Required] and [RegularExpression] attributes to handle validation. If you take a look at the Prism for WinRT Universal Converged Branch on Codeplex, you'll note that even the Prism team's AdventureWorks Shopper app has the Data Annotations commented out due to lack of support in the Universal libraries provided by Microsoft.
In order to work around this, I wrote a simple (albeit verbose) approach to handling data validation. You can validate your model objects and the base class will handle notifying the UI bindinds that validation failed.
I have a blog post explaining why I went with this approach. The post is helpful for understanding why I wrote it how I did, but is a bit outdated from the actual source. The source comes with a sample Universal WinRT project targeting both Windows 8.1 and Windows Phone 8.1, with complete validation.

Answer 2

Any app that accepts input from users should ensure that the data is valid. An app could, for example, check that the input contains only characters in a particular range, is of a certain length, or matches a particular format. Without validation, a user can supply data that causes the app to fail. Validation enforces business rules, and prevents an attacker from injecting malicious data.
[Required(ErrorMessageResourceType = typeof(ErrorMessagesHelper), ErrorMessageResourceName = "RequiredErrorMessage")]
[RegularExpression(NAMES_REGEX_PATTERN, ErrorMessageResourceType = typeof(ErrorMessagesHelper), ErrorMessageResourceName = "RegexErrorMessage")]
public string FirstName
{
get { return _firstName; }
set { SetProperty(ref _firstName, value); }
}
http://code.msdn.microsoft.com/windowsapps/Prism-for-WinRTValidatableB-2acb9892
http://msdn.microsoft.com/en-us/library/windows/apps/xx130659.aspx