C#基础知识学习之 ✨ “精神小伙“——委托(delegate) 的含义和用法

https://blog.csdn.net/zhangay1998/article/details/115697668

C#委托（Delegate）

在C#的学习过程中，自然有我们的精神小伙——委托的一席之地
本文就介绍一下C#中的委托，这位可以包含同类方法函数的小伙子

C# 中的委托（Delegate）类似于 C 或 C++ 中函数的指针。委托（Delegate）
是存有对某个方法的引用的一种引用类型变量。引用可在运行时被改变。委托就是用来储存方法的结构
委托（Delegate）特别用于实现事件和回调方法。所有的委托（Delegate）都派生自 System.Delegate 类。

声明和定义委托分为4个步骤

声明一个委托（函数指针）
创建委托对象
创造符合委托格式的函数（指针指向的函数）
将函数名称赋值给委托

Tips:委托对象为空是不能执行的，执行前先提前判断

代码实例如下

// 1. 声明一个委托（函数指针）
delegate void delegateTest(int a,float b);
// delegate 返回值类型 委托类型名（参数列表）：


// 2. 创建委托对象 

public delegateTest dT1;




//3. 创造符合委托格式的函数（指针指向的函数）

public void Test(int a,float b)

{

a+=100;

b*=2.0;

Console.WriteLine("a:{0},b:{1}", a,b);

}




static void Main(string[] args)

{

// 4.  将函数名称赋值给委托

dT1=new delegateTest(Test);

//使用委托

dT1(1,1.0);



<span class="token comment">//打印结果</span>
<span class="token comment">//a=101,b=2.0</span>




}


<span class="token comment">//打印结果</span>
<span class="token comment">//a=101,b=2.0</span>

委托类型

委托/代理：句柄
委托是自定义类型
委托是引用类型

几种基础的委托结构

自定义委托语法： delegate 返回类型委托名([参数]);
Action内置委托语法： Action<[参数类型0-16个]> 委托名=被委托方法名;
Func内置委托语法： Function<[参数类型0-16个]，返回类型> 委托名=被委托方法名；
多播委托语法：委托名+=被委托方法名；委托名-=被委托方法名；

委托的用法

下面的实例演示了委托的一个用法，可以将定义的委托作为参数，就可以直接通过委托来调用委托中的方法了。

//声明委托
public delegate void OndelegateTest(int a,int b);

   <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">TestNum1</span><span class="token punctuation">(</span><span class="token keyword">int</span> i，<span class="token keyword">int</span> j<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     <span class="token keyword">int</span> num <span class="token operator">=</span> i<span class="token operator">+</span>j<span class="token punctuation">;</span>
     Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token string">"num:"</span><span class="token operator">+</span>num<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
   <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">TestNum2</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">,</span><span class="token keyword">int</span> j<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     <span class="token keyword">int</span> num <span class="token operator">=</span> i<span class="token operator">*</span>j<span class="token punctuation">;</span>
     Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token string">"num:"</span><span class="token operator">+</span>num<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
  
  <span class="token comment">// 该方法把委托作为参数，并使用它调用方法</span>
  <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">sendNum</span><span class="token punctuation">(</span><span class="token class-name">OndelegateTest</span> test<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     <span class="token function">test</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>




static void Main(string[] args)

{

OndelegateTest d1=new OndelegateTest(TestNum1);

OndelegateTest d2=new OndelegateTest(TestNum2);

sendNum(d1);

sendNum(d2);

Console.ReadKey();

}


   <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">TestNum1</span><span class="token punctuation">(</span><span class="token keyword">int</span> i，<span class="token keyword">int</span> j<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     <span class="token keyword">int</span> num <span class="token operator">=</span> i<span class="token operator">+</span>j<span class="token punctuation">;</span>
     Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token string">"num:"</span><span class="token operator">+</span>num<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
   <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">TestNum2</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">,</span><span class="token keyword">int</span> j<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     <span class="token keyword">int</span> num <span class="token operator">=</span> i<span class="token operator">*</span>j<span class="token punctuation">;</span>
     Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token string">"num:"</span><span class="token operator">+</span>num<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
  
  <span class="token comment">// 该方法把委托作为参数，并使用它调用方法</span>
  <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">sendNum</span><span class="token punctuation">(</span><span class="token class-name">OndelegateTest</span> test<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     <span class="token function">test</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>

委托的多播（Multicasting of a Delegate）

委托对象可使用 “+” 运算符进行合并。一个合并委托调用它所合并的两个委托。只有相同类型的委托可被合并。"-" 运算符可用于从合并的委托中移除组件委托。

使用委托的这个有用的特点，您可以创建一个委托被调用时要调用的方法的调用列表。这被称为委托的多播（multicasting），也叫组播。下面的程序演示了委托的多播：

using System;
//声明委托
delegate int NumberChanger(int n);
namespace DelegateAppl
{
   class TestDelegate
   {
      static int num = 10;
      public static int AddNum(int p)
      {
         num += p;
         return num;
      }

  <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">int</span> <span class="token function">MultNum</span><span class="token punctuation">(</span><span class="token keyword">int</span> q<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     num <span class="token operator">*</span><span class="token operator">=</span> q<span class="token punctuation">;</span>
     <span class="token keyword">return</span> num<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
   <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">int</span> <span class="token function">TestNum</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     num <span class="token operator">-</span><span class="token operator">=</span> i<span class="token punctuation">;</span>
     <span class="token keyword">return</span> num<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">int</span> <span class="token function">getNum</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     <span class="token keyword">return</span> num<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>

  <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">Main</span><span class="token punctuation">(</span><span class="token keyword">string</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     <span class="token comment">// 创建委托实例</span>
     <span class="token class-name">NumberChanger</span> nc<span class="token punctuation">;</span>
     <span class="token class-name">NumberChanger</span> nc1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">NumberChanger</span><span class="token punctuation">(</span>AddNum<span class="token punctuation">)</span><span class="token punctuation">;</span>
     <span class="token class-name">NumberChanger</span> nc2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">NumberChanger</span><span class="token punctuation">(</span>MultNum<span class="token punctuation">)</span><span class="token punctuation">;</span>
     nc <span class="token operator">=</span> nc1<span class="token punctuation">;</span>
     nc <span class="token operator">+</span><span class="token operator">=</span> nc2<span class="token punctuation">;</span>
     nc <span class="token operator">+</span><span class="token operator">=</span> TestNum<span class="token punctuation">;</span>
     <span class="token comment">// 调用多播</span>
     <span class="token function">nc</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
     Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token string">"Value of Num: {0}"</span><span class="token punctuation">,</span> <span class="token function">getNum</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
     Console<span class="token punctuation">.</span><span class="token function">ReadKey</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>




}

}


  <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">int</span> <span class="token function">MultNum</span><span class="token punctuation">(</span><span class="token keyword">int</span> q<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     num <span class="token operator">*</span><span class="token operator">=</span> q<span class="token punctuation">;</span>
     <span class="token keyword">return</span> num<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
   <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">int</span> <span class="token function">TestNum</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     num <span class="token operator">-</span><span class="token operator">=</span> i<span class="token punctuation">;</span>
     <span class="token keyword">return</span> num<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">int</span> <span class="token function">getNum</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     <span class="token keyword">return</span> num<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>

  <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">Main</span><span class="token punctuation">(</span><span class="token keyword">string</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     <span class="token comment">// 创建委托实例</span>
     <span class="token class-name">NumberChanger</span> nc<span class="token punctuation">;</span>
     <span class="token class-name">NumberChanger</span> nc1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">NumberChanger</span><span class="token punctuation">(</span>AddNum<span class="token punctuation">)</span><span class="token punctuation">;</span>
     <span class="token class-name">NumberChanger</span> nc2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">NumberChanger</span><span class="token punctuation">(</span>MultNum<span class="token punctuation">)</span><span class="token punctuation">;</span>
     nc <span class="token operator">=</span> nc1<span class="token punctuation">;</span>
     nc <span class="token operator">+</span><span class="token operator">=</span> nc2<span class="token punctuation">;</span>
     nc <span class="token operator">+</span><span class="token operator">=</span> TestNum<span class="token punctuation">;</span>
     <span class="token comment">// 调用多播</span>
     <span class="token function">nc</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
     Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token string">"Value of Num: {0}"</span><span class="token punctuation">,</span> <span class="token function">getNum</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
     Console<span class="token punctuation">.</span><span class="token function">ReadKey</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>

当上面的代码被编译和执行时，它会产生下列结果：

Value of Num: 70

委托对象的绑定与解绑

     delegate int NumberChanger(int n);
     NumberChanger nc;

 <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">int</span> <span class="token function">TestNum</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     num <span class="token operator">-</span><span class="token operator">=</span> i<span class="token punctuation">;</span>
     <span class="token keyword">return</span> num<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
  
 nc <span class="token operator">+</span><span class="token operator">=</span> TestNum<span class="token punctuation">;</span><span class="token comment">//委托的绑定</span>
 nc <span class="token operator">-</span><span class="token operator">=</span> TestNum<span class="token punctuation">;</span><span class="token comment">//委托的解绑</span>


 <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">int</span> <span class="token function">TestNum</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span>
  <span class="token punctuation">{<!-- --></span>
     num <span class="token operator">-</span><span class="token operator">=</span> i<span class="token punctuation">;</span>
     <span class="token keyword">return</span> num<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
  
 nc <span class="token operator">+</span><span class="token operator">=</span> TestNum<span class="token punctuation">;</span><span class="token comment">//委托的绑定</span>
 nc <span class="token operator">-</span><span class="token operator">=</span> TestNum<span class="token punctuation">;</span><span class="token comment">//委托的解绑</span>