ValidationAdapter.cs

using FluentValidation;
using Stylet;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace CreditCalc
{
	public class ValidationAdapter<T> : IModelValidator<T>
	{
		private readonly IValidator<T> validator;
		private T subject;

		public ValidationAdapter(IValidator<T> validator)
		{
			this.validator = validator;
		}

		public void Initialize(object subject)
		{
			this.subject = (T)subject;
		}

		public Task<IEnumerable<string>> ValidatePropertyAsync(string propertyName)
		{
			var errors = this.validator.Validate(this.subject, propertyName).Errors.Select(x => x.ErrorMessage);
			return Task.FromResult(errors);
		}

		public async Task<Dictionary<string, IEnumerable<string>>> ValidateAllPropertiesAsync()
		{
			// If someone's calling us synchronously, and ValidationAsync does not complete synchronously,
			// we'll deadlock unless we continue on another thread.
			return (await this.validator.ValidateAsync(this.subject).ConfigureAwait(false))
				.Errors.GroupBy(x => x.PropertyName)
				.ToDictionary(x => x.Key, x => x.Select(failure => failure.ErrorMessage));
		}
	}
}