Attribute 示例

假设 外语老师 是一个类，
那么 外语老师 应该具有这样的特性：会说外语
并且 会说外语 这一特性又包含一些信息，比如：外语种类、外语水平、其它信息。

 

按照这样的理解，应该有下面的实现。

using System;

using System.Reflection;


namespace Test_Console

{

    //自定义一个特性，名为 CanSpeakForeignLanguage ，继承自 System.Attribute  

    [AttributeUsage(AttributeTargets.All, AllowMultiple = true, Inherited = false)]

    public class CanSpeakForeignLanguage : System.Attribute

    {

        private string _languageType;

        private int _languageLevel;

        private string _languageInfo;


        //必须定义其构造函数，如果不定义有编译器提供无参默认构造函数   

        public CanSpeakForeignLanguage(){}


        public CanSpeakForeignLanguage(string languageType, int languageLevel)

        {

            _languageType = languageType;

            _languageLevel = languageLevel;

        }




        //定义属性   

        //特性和属性不是一回事  

        public string LanguageType

        {

            get { return _languageType == null ? string.Empty : _languageType; }

        }


        public int LanguageLevel

        {

            get { return _languageLevel; }

        }


        public string LanguageInfo

        {

            get { return _languageInfo; }

            set { _languageInfo = value; }

        }


        //定义方法   

        public void CanSpeak()

        {

            Console.WriteLine("He can speak {0}.", _languageType == null ? "Chinese Only" : _languageType);

        }

    }



    //定义一个类，LanguageTeacher ，这个类具有 CanSpeakForeignLanguage 特性  

    [CanSpeakForeignLanguage("English", 8, LanguageInfo = "This is US English, but not England English.")]

    public class LanguageTeacher

    {

        public void SayHello()

        {

            Console.WriteLine("Hello, I'm a Foreign Language teacher, I can speak Foreign Language.");

        }

    }




    //主程序   

    class Program

    {

        static void Main(string[] args)

        {

            Type type = typeof(LanguageTeacher);

            MemberInfo memberinfo = type;


            //利用反射获得 LanguageTeacher 所具有的特性信息，赋值给 can  

            CanSpeakForeignLanguage can = (CanSpeakForeignLanguage)Attribute.GetCustomAttribute(memberinfo,

                                                                            typeof(CanSpeakForeignLanguage));


            //输出 LanguageTeacher 的特性信息  

            if (can != null)

            {

                Console.WriteLine("Class of LanguageTeacher Can Speak: " + can.LanguageType);

                Console.WriteLine("The English Level of LanguageTeacher is: " + can.LanguageLevel);

                Console.WriteLine("And, " + can.LanguageInfo);

            }


            Console.WriteLine();

            //反射创建 LanguageTeacher 对象，执行它的 SayHello 方法  

            object obj = Activator.CreateInstance(type);

            MethodInfo mi = type.GetMethod("SayHello");

            mi.Invoke(obj, null);

        }

    }

}

作者：luckdv

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