Why can't I use resources as ErrorMessage with DataAnnotations?

Question

Why can\'t I do like this?

[Required(ErrorMessage = \"*\")]
[RegularExpression(\"^[a-zA-Z0-9_]*$\", ErrorMessage = Resources.RegistrationModel.UsernameError)         


        

Answer 1

Try FluentModelMetaDataProvider.

Managed to use resources for error messages in strongly typed fashion.

Looks like this:

using System.Web.Mvc.Extensibility;

namespace UI.Model
{
    public class StoreInputMetadata : ModelMetadataConfigurationBase
    {
        public StoreInputMetadata()
        {
            Configure(m => m.Id)
                .Hide();
            Configure(model => model.Name)
                .Required(Resources.Whatever.StoreIsRequired)
                .MaximumLength(64, Resources.Whatever.StoreNameLengthSomething);
        }
    }
}

---

What is the error message telling me?

An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type.

It's already self explanatory. C# isn't dynamic language like Ruby where You can write classes that inherits random base class at runtime. :)

Here's what Skeet says about this.