Can Verifiers be Asynchronous?

          Thanks for the latest sample.

          If I make a Company Name error by entering @ as part of the name, it shows the error correctly, but as mentioned earlier the error is duplicated if I tab back to the same field. After correcting the error, the user is expected to come back to the filed twice to clear all the existing errors. Do you still think it is the problem with DataGrid/INotifyDataErrorInfo? If so, do you know why we do not see such a behavior when doing Synchronous Validations?

         Also, the ValidationError is removed by checking for '@' in the error message. It is possible that we might have such characters in other error messages or we may not have such a text to look for in our messages. Is there a better implementation for this? Is there a tag property or something like that for validation error which we can set when a specific error message is generated (may be, a unique Message ID) so that we can look for such immutable property and remove those errors.

          For example, if we have validations to make sure that Name and ID must be unique (checked async), the messages might be just 'Must be Unique'  or 'ID must be unique.' or 'Description must be unique.'. It might be difficult to remove such messages. Another alternative might be to regenerate the same message and look for its existence and remove it. However, this won’t work if we have generic messages like ‘Must be unique’ and the context is added dynamically as part of displaying error summary.

          Thanks again for your help.

           I tried this solution and it works with adding validation results to the collection. 

           However, if the same error occurs again for a different value for the same property (after the initial error), the error is added again to the validation summary control unlike the Verifier Engine behavior, which is only one entry in the Validation Summary even if the same verifier error occurs for the same property multiple times.  Do we need to have custom logic to avoid getting duplicate messages?

On a similar note, how do we remove the message after the Async call succeeds? If I try to remove the validation error by calling EntityAspect.ValidationErrors.Remove(), the message is removed from the collection, but the property still shows as in error and the ValidationSummary also shows the error.  Do we need to do anything else apart from removing the validation result from the ValidationErrors collection?

Thanks.