How to change attribute error message

Question

I am overriding the RequiredAttribute and in my IsValid method I need the ability to change the ErrorMessage property. Is this possible?

Answer 1

[Required(ErrorMessage = "Some custom required message about the Foo property")]
public string Foo { get; set; }

and inside the IsValid method:

public class MyRequiredAttribute : RequiredAttribute
{
    public override bool IsValid(object value)
    {
        ErrorMessage = "Some custom required message";
        ...
        return base.IsValid(value);
    }
}