By default, Catel registers the AttributeValidatorProvider as the IValidatorProvider. This way the ModelBase and all the classes that derive from it can easily add a custom validator by using the ValidateModelAttribute.

Note that it is still possible to register a custom IValidatorProvider to customize this behavior. It is even possible to set the Validator property of the ModelBase on a specific instance of a model

Implementing the validator

The first thing that needs to be done is to write a custom implementation of the IValidator interface. You can either implement all the members yourself or derive from ValidatorBase as is shown below:

public class PersonValidator : ValidatorBase<PersonModel>
{
	protected override void ValidateFields(PersonModel instance, List<IFieldValidationResult> validationResults)
	{
		if (string.IsNullOrWhiteSpace(instance.FirstName))
		{
			validationResults.Add(FieldValidationResult.CreateError(PersonModel.FirstNameProperty, "First name is required"));
		}
 
		if (string.IsNullOrWhiteSpace(instance.LastName))
		{
			validationResults.Add(FieldValidationResult.CreateError(PersonModel.FirstNameProperty, "First name is required"));
		}
	}
 
	protected override void ValidateBusinessRules(PersonModel instance, List<IBusinessRuleValidationResult> validationResults)
	{
	    // No business rules validations yet
	}
}

Decorating a model with the attribute

Once a validator is available, the only thing that needs to be done is to decorate the model with the ValidateModelAttribute:

[ValidateModel(typeof(PersonValidator))]
public class PersonModel : ModelBase
{
	public string FirstName
	{
		get { return GetValue<string>(FirstNameProperty); }
		set { SetValue(FirstNameProperty, value); }
	}

	public static readonly PropertyData FirstNameProperty = RegisterProperty("FirstName", typeof(string), string.Empty);

	public string LastName
	{
		get { return GetValue<string>(LastNameProperty); }
		set { SetValue(LastNameProperty, value); }
	}

	public static readonly PropertyData LastNameProperty = RegisterProperty("LastName", typeof(string), string.Empty);
}

The custom validator will now automatically be called.

Catel - LATEST

Validation via special model validators

Implementing the validator