/// <summary>

    /// 使用特性，可以有效地将元数据或声明性信息与代码（程序集、类型、方法、属性等）相关联。 将特性与程序实体相关联后，可以在运行时使用反射这项技术查询特性

    /// </summary>

    ///

    [System.AttributeUsage(System.AttributeTargets.Class|System.AttributeTargets.Struct,AllowMultiple = true)]

    public class Author : System.Attribute

    {

        string name;

        public double version;

        public Author(string name)

        {

            this.name = name;

            version = 1.0;

        }

        public string GetName()

        {

            return name;

        }

    }

    // Class with the Author attribute.

    [Author("P. Ackerman")]

    public class FirstClass

    {

        // ...

    }

    // Class without the Author attribute.

    public class SecondClass

    {

        // ...

    }

    // Class with multiple Author attributes.

    [Author("P. Ackerman"), Author("R. Koch", version = 2.0)]

    public class ThirdClass

    {

        // ...

    }

    class TestAuthorAttribute

    {

       public  static void Test()

        {

            PrintAuthorInfo(typeof(FirstClass));

            PrintAuthorInfo(typeof(SecondClass));

            PrintAuthorInfo(typeof(ThirdClass));

        }

        private static void PrintAuthorInfo(System.Type t)

        {

            System.Console.WriteLine("Author information for {0}", t);

            System.Attribute[] attrs = System.Attribute.GetCustomAttributes(t);

            foreach(System.Attribute attr in attrs)

            {

                if(attr is Author)

                {

                    Author a = (Author)attr;

                    System.Console.WriteLine("   {0}, version {1:f}", a.GetName(), a.version);

                }

            }

        }

    }