动态设置attribute 动态设置特性、动态设置C#前的方括号[]

代码：

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
    }
}