具有返回类型的代表 [英] Delegates with return type

问题描述

您好我有两个方法，返回类型1是实例，另一个是静态方法。我试图用代理访问这些方法，但我无法访问它我收到错误错误的返回类型

 < span class =code-keyword>使用系统; 
 使用 System.Collections.Generic; 
  using  System.Linq; 
  using  System.Text; 
 
  namespace  Delgates_Ex1 
 {
 
  public   delegate   void  ExampleDelgate（ int  x， int  y）; 
 
 
  class 民主党
 {
  public   int 添加（ int  x， int  y）
 
 {
 
 Console.WriteLine（ 加法方法）; 
  return （x + y）; 
 
} 
 
 
  public   static   int  mul（ int  x， int  y）
 {
 Console.WriteLine（ 乘法方法）; 
 
  return （x * y）; 
} 
 
} 
 
 
  class 计划
 {
 
 静态  void  Main（ string  [] args）
 {
 Democlass d =  new  Democlass（）; 
 
 ExampleDelgate ed =  new  ExampleDelgate（d.Add）; 
 
 ed（ 30 ， 10 ）; 
 
 Console.WriteLine（  \ n）; 
 
 ed =  new  ExampleDelgate（Democlass.mul）; 
 ed（ 30  *  10 ）; 
 
} 
} 
} 

解决方案

更改代表的退货类型从 void 到 int ：

  public   delegate   int  ExampleDelgate（ int  x， int  y）; 

此外，当你尝试使用委托访问 mul 方法，您应该传递 30 和 10 作为参数而不是乘法：

 ed =  new  ExampleDelgate（Democlass.mul） ; 
  //   ed（30 * 10）; //删除此行 
 ed（ 30 ， 10 ）;  //  添加此 

ProgramFOX已经解决了您的问题，但是您也可能会发现此CodeProject文章很有用 - C＃ - Delegates 101 - 一个实际例子 [ ^ ]

除了正确的解决方案1：



您不需要单独的委托类型声明如此简单的签名;它已经为你完成了，并且是 System.Func< int，int，int> 。您根本不需要单独的类型声明：

 System.Func< int， int ，int> ed =  new  System.Func< int， int ，int>（Demo.Mul）; 

此外，您甚至不需要单独的（命名）方法实现：

 System.Func< int， int ，int> ed =  new  System.Func< int， int ，int>（（x，y）= >  {
  return  x * y; 
}）; 

使用lambda的特殊功能：您可以在某些方法中将上面显示的内容设置为本地，而不是在其他任何地方暴露。你为什么需要这样的东西？仅举一件事，请参阅我的短文：隐藏调用方法主体内部的特殊方法 [ ^ ]。

-SA

Hi I have two methods with return type one being instance and the other one is static method. I am trying to access those methods with delegates but i am unable to access it i get a error " Has wrong return type

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Delgates_Ex1
{

    public delegate void ExampleDelgate (int x, int y);


    class Democlass
    {
        public int Add(int x, int y)

        {

            Console.WriteLine("Addition Method");
            return (x + y);
              
        }


        public static int mul(int x, int y)
        {
            Console.WriteLine("Multiplication Method");

            return (x * y);
        }

    }


    class Program
    {

        static void Main(string[] args)
        {
            Democlass d = new Democlass();

            ExampleDelgate ed = new ExampleDelgate(d.Add);

            ed(30, 10);

            Console.WriteLine("\n");

            ed = new ExampleDelgate(Democlass.mul);
            ed(30 * 10);

        }
    }
}

解决方案

Change the return type of your delegate from void to int:

public delegate int ExampleDelgate (int x, int y);

Also, when you try to access the mul method with a delegate, you should pass 30 and 10 as parameters and not as a multiplication:

ed = new ExampleDelgate(Democlass.mul);
//ed(30 * 10); // remove this line
ed(30, 10); // add this

ProgramFOX has solved your problem, however you may also find this CodeProject article useful - C# - Delegates 101 - A Practical Example[^]

In addition to the correct Solution 1:

You don't need a separate delegate type declaration for such a simple signature; it is already done for you and is System.Func<int, int, int>. You don't need a separate type declaration at all:

System.Func<int, int, int> ed = new System.Func<int, int, int>(Demo.Mul);

Moreover, you don't even need a separate (named) method implementation:

System.Func<int, int, int> ed = new System.Func<int, int, int>( (x, y) => {
    return x * y;
});

The special feature of using lambda: you can make the like shown above local in some method, not exposed anywhere else. Why would you need such a thing? For just one thing, please see my short article: Hide Ad-hoc Methods Inside the Calling Method’s Body[^].

—SA

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