Get error message when using custom validation attribute

Question

I'm using the CustomValidationAttribute like this

[CustomValidation(typeof(MyValidator),"Validate",ErrorMessage = "Foo")]

And my validator contains this code

public class MyValidator {
    public static ValidationResult Validate(TestProperty testProperty, ValidationContext validationContext) {
        if (string.IsNullOrEmpty(testProperty.Name)) {
            return new ValidationResult(""); <-- how can I get the error message  from the custom validation attribute? 
        }
        return ValidationResult.Success;
    }
}

So how can I get the error message from the custom validation attribute?

Answer 1

There's no reliable way to get the error message from the attribute. Alternatively you could write a custom validation attribute:

[MyValidator(ErrorMessage = "Foo")]
public TestProperty SomeProperty { get; set; }

like this:

public class MyValidatorAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var testProperty = (TestProperty)value;
        if (testProperty == null || string.IsNullOrEmpty(testProperty.Name))
        {
            return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
        }

        return null;
    }
}

In this case the error message will be inferred from the custom validation attribute.