2019独角兽企业重金招聘Python工程师标准>>> 
建立一个C#控制台应用程序AttributeTest。
建立一个类Operations，代码如下：
namespace AttributeTest
{public class Operations{public static int Add(int a, int b) { return a + b; }public static int Minus(int a, int b) { return a - b; }public static int Multiply(int a, int b) { return a * b; }public static int Divide(int a, int b) { return a / b; }public static int Modulo(int a, int b) { return a % b; }}
}一种调用指定函数的方式，是建立一个函数UseOperation2和一个委托。将要调用的Operations内函数作为参数传入到UseOperation2中：
public delegate TOutput OperDelegate<TInput, TOutput>(TInput input1, TInput input2);public static void UseOperation2<TInput, TOutput>(OperDelegate<TInput, TOutput> operDelegate, TInput input1, TInput input2)
{TOutput output = operDelegate(input1, input2); Console.WriteLine(string.Format("{0} {1} {2} = {3}",input1, operDelegate.Method.Name, input2, output));
}在Main函数内写如下代码：
Console.WriteLine("调用Operations类内各函数：");
UseOperation2(Operations.Add, 3, 5);
UseOperation2(Operations.Minus, 9, 4);
UseOperation2(Operations.Multiply, 3, 7);
UseOperation2(Operations.Divide, 8, 2);
UseOperation2(Operations.Modulo, 15, 4);输出结果如下：
如果不想以函数作为参数传递，还可以通过为Operations类内的函数添加特性来解决这一问题。
建立一个特性类OperateAttribute：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace AttributeTest
{/// <summary>/// 运算特性/// </summary>[AttributeUsage(AttributeTargets.Method)]public class OperateAttribute : Attribute{/// <summary>/// 运算特性/// </summary>/// <param name="operateNo">运算代号</param>public OperateAttribute(string operateNo){this.operateNo = operateNo;}/// <summary>/// 运算代号/// </summary>string operateNo;/// <summary>/// 运算代号/// </summary>public string OperNo{get{return operateNo;}}}
}这个时候需要修改一下Operations类下个函数，为它们逐个添加刚刚实现的特性Operate：
namespace AttributeTest
{public class Operations{[Operate("ADD")]public static int Add(int a, int b) { return a + b; }[Operate("MINUS")]public static int Minus(int a, int b) { return a - b; }[Operate("MULTIPLY")]public static int Multiply(int a, int b) { return a * b; }[Operate("DIVIDE")]public static int Divide(int a, int b) { return a / b; }[Operate("MOD")]public static int Modulo(int a, int b) { return a % b; }}
}要反射标记了我们指定特性的函数的细节，可以在Main方法旁边实现如下函数：
/// <summary>
/// 打印Operations类内各函数属性
/// </summary>
public static void PrintOperations()
{foreach (MethodInfo mInfo in (new Operations()).GetType().GetMethods()){foreach (Attribute attr in Attribute.GetCustomAttributes(mInfo)){if (attr is OperateAttribute){string operNo = (attr as OperateAttribute).OperNo;Console.WriteLine("=====================");Console.WriteLine("关联属性：" + mInfo.Attributes);Console.WriteLine("函数名称：" + mInfo.Name);Console.WriteLine("成员类型：" + mInfo.MemberType);Console.WriteLine("参数0类型：" + mInfo.GetParameters()[0].ParameterType.ToString());Console.WriteLine("参数1类型：" + mInfo.GetParameters()[1].ParameterType.ToString());Console.WriteLine("返回值类型：" + mInfo.ReturnParameter.ParameterType.ToString());}}}
}在Main方法中添加代码：
Console.WriteLine("打印Operations类内各函数属性：");
PrintOperations();输出结果如下：
要通过指定Operate特性值来决定调用哪个函数，可以在Main方法旁边实现如下函数：
/// <summary>
/// 调用Operations类内各函数
/// </summary>
/// <param name="operNo">运算代号</param>
/// <param name="a">运算符a</param>
/// <param name="b">运算符b</param>
public static void UseOperation(string operNo, int a, int b)
{foreach (MethodInfo mInfo in (new Operations()).GetType().GetMethods()){foreach (Attribute attr in Attribute.GetCustomAttributes(mInfo)){if (attr is OperateAttribute && (attr as OperateAttribute).OperNo == operNo){Console.WriteLine(string.Format("{0} {1} {2} = {3}",a, operNo, b, mInfo.Invoke(null, new object[] { a, b })));}}}
}在Main方法中添加如下代码：
Console.WriteLine("调用Operations类内各函数：");
UseOperation("ADD", 3, 5);
UseOperation("MINUS", 9, 4);
UseOperation("MULTIPLY", 3, 7);
UseOperation("DIVIDE", 8, 2);
UseOperation("MOD", 15, 4);输出结果如下：
END
