Modifying Class Attribute on Runtime

Question

I am not sure if it is possible I have seen:
Change Attribute\'s parameter at runtime.
My case is very similar but I am trying to change the attribute of a class in

Answer 1

You need to code your attribute so that it supports runtime values. For example, the validation attributes support Internationalization of messages through the setting of a resource type and resource string as opposed to the static Message string.

Another approach is to use a IOC container such as StructureMap or Unity to provide some object/service that provides the values.

If you don;t want to couple your attribute to a particular container, use the Common ServiceLocator wrapper provided by the Patterns and Practices group.

Answer 2

If you use reflection, then not quite like this - reflection attributes can't be substituted - only the component-model view is impacted by TypeDescriptor. However, you can subclass CategoryAttribute to your purposes. Especially useful for i18n.

using System.ComponentModel;
using System;
[MyCategory("Fred")]
class Foo {  }
static class Program
{
    static void Main()
    {
        var ca = (CategoryAttribute)Attribute.GetCustomAttribute(typeof(Foo), typeof(CategoryAttribute));
        Console.WriteLine(ca.Category);
              // ^^^ writes "I was Fred, but not I'm EVIL Fred"
    }
}
class MyCategoryAttribute : CategoryAttribute
{
    public MyCategoryAttribute(string category) : base(category) { }
    protected override string GetLocalizedString(string value)
    {
        return "I was " + value + ", but not I'm EVIL " + value;
    }
}

Answer 3

Avoiding reflection entirely, you can do this via TypeDescriptor:

using System;
using System.ComponentModel;
using System.Linq;
[Category("nice")]
class Foo {  }
static class Program
{
    static void Main()
    {
        var ca = TypeDescriptor.GetAttributes(typeof(Foo))
              .OfType<CategoryAttribute>().FirstOrDefault();
        Console.WriteLine(ca.Category); // <=== nice
        TypeDescriptor.AddAttributes(typeof(Foo),new CategoryAttribute("naughty"));
        ca = TypeDescriptor.GetAttributes(typeof(Foo))
              .OfType<CategoryAttribute>().FirstOrDefault();
        Console.WriteLine(ca.Category); // <=== naughty
    }
}