ReactiveValidation: data validation in WPF

• Rules are created through the fluent interface
• Full internal control over property changes
• Localization support (including on the fly)
• Displaying Messages in the GUI

private override void Execute()
{
    if(string.IsNullOrEmpty(Property1) == true)
    {
        MessageBox.Show("Необходимо указать Property1");
        return;
    }
    if(Property2 < Property3)
    {
        MessageBox.Show("Property2 должно быть не меньше Property3");
        return;
    }
    ...
    //отправка данных серверу
    do();
}

public class ViewModel : BaseViewModel
{
    [IsRequired]
    public string Property1 { get {...} set {...} }
    [CustomValidation(typeof(ViewModel), nameof(ValidateProperty2))]
    public int? Property2 { get {...} set {...} }
    public int? Property3 { get {...} set {...} }
    [UsedImplicitly]
    public static ValidationResult ValidateProperty2(int? property2, ValidationContext validationContext)
    {
        var viewModel = (ViewModel)validationContext.ObjectInstance;
        if (viewModel.Property2 < viewModel.Property3)
        {
            return new ValidationResult("Property2 должно быть не меньше Property3");
        }
        return ValidationResult.Success;
    }
}

public class CarViewModel : ValidatableObject
{
    public CarViewModel()
    {
        Validator = GetValidator();
    }
    private IObjectValidator GetValidator()
    {
        var builder = new ValidationBuilder();
        builder.RuleFor(vm => vm.Make).NotEmpty();
        builder.RuleFor(vm => vm.Model).NotEmpty().WithMessage("Please specify a car model");
        builder.RuleFor(vm => vm.Mileage).GreaterThan(0).When(model => model.HasMileage);
        builder.RuleFor(vm => vm.Vin).Must(BeAValidVin).WithMessage("Please specify a valid VIN");
        builder.RuleFor(vm => vm.Description).Length(10, 100);
        return builder.Build(this);
    }
    private bool BeAValidVin(string vin)
    {
        //Здесь проверяем VIN номер на корректность
    }
    //Далее следуют свойства с реализацией INotifyPropertyChanged
}

xmlns:b="clr-namespace:ReactiveValidation.WPF.Behaviors;assembly=ReactiveValidation"
...

builder.RuleFor(vm => vm.PhoneNumber)
    .NotEmpty()
        .When(vm => Email, email => string.IsNullOrEmpty(email) == true)
        .WithMessage("You need to specify a phone or email")
    .Matches(@"^\d{11}$")
        .WithMessage("Phone number must contain 11 digits");

[DisplayName(DisplayName = "Minimal amount")]
public int MinAmount { get; set; }

builder.RuleFor(vm => vm.Email)
    .NotEmpty()
        .When(vm => PhoneNumber, phoneNumber => string.IsNullOrEmpty(phoneNumber) == true)
        .WithLocalizedMessage(nameof(Resources.Default.PhoneNumberOrEmailRequired))
    .Matches(@"^\w+@\w+.\w+$")
        .WithLocalizedMessage(Resources.Additional.ResourceManager, nameof(Resources.Additional.NotValidEmail));

[DisplayName(DisplayNameKey = nameof(Resources.Default.PhoneNumber))]
public string PhoneNumber { get; set; }
[DisplayName(ResourceType = typeof(Resources.Additional), DisplayNameKey = nameof(Resources.Additional.Email))]
public string Email { get; set; }

• Changing localization on the fly is based on the fact that inside the ValidationMessage class, a subscription to the event of the LanguageManager class occurs
• Subscription occurs only if the TrackCultureChanged property is true. Therefore, it should be set only once - at the start of the application and no longer change.
• If the culture is changed using CultureInfo.CurrentUICulture, after changing it, call the ValidationOptions.LanguageManager.OnCultureChanged () method

• There are 2 main types of messages: Error (error) and warning (Warining). Warnings are also displayed on the GUI (only in orange), but the model is considered valid. In addition, there is a gradation of ordinary / simple (Simple). Regular messages are displayed when focusing or hovering over the control, while simple messages only when hovering
• The rules are based on extensions methods, so you can easily extend them with your own validators
• The basic interface required for a validated object is IValidatableObject. There is an INPC based ValidatableObject implementation in the library. You can easily define your own base class with this interface, since its implementation contains a bit of code (the project shows examples with an override from ReactiveObject from Reactive UI)
• If a property inherited from INotifyPropertyChanged or INotifyCollectionChanged is validated, special adapter classes monitor their invocation, initiating revalidation. You can expand your subscriptions with your classes, for example, add IReactiveNotifyCollectionItemChanged <> from the Reactive UI

• There is no asynchronous validation. I think we can debate about whether it is needed or not, but nevertheless, now it is not supported.
• I am ashamed, but errors are possible. I hope that they will be quickly found and fixed.
• This is my first development experience for Open Source. I am very worried that the opportunities that I invested initially will not be enough. Hope this is also easily fixable.

• FluentValidation , which I often see in applications like Web API
• Reactive UI , in addition I recommend this series of articles ( first , second and third parts)