C# 入门教程（四）委托详解 - 教程

文章目录

1、什么是委托

在 C#里，委托属于引用类型，其作用是封装和引用一个或多个方法。可以把它想象成一种类型安全的函数指针，不过它比函数指针更强大，因为它支持多播（也就是可以引用多个方法）。委托经常会在事件处理、回调函数以及异步编程中被用到。

  • 委托(delegate)是函数指针的"升级版"

    • 实例:C/C++中的函数指针
    #include <stdio.h>
  // 函数：加法
  int add(int a, int b) {
  return a + b;
  }
  // 函数：减法
  int subtract(int a, int b) {
  return a - b;
  }
  int main() {
  // 声明一个函数指针
  int (*operation)(int, int);
  // 让函数指针指向add函数
  operation = add;
  printf("加法结果: %d\n", operation(5, 3));
  // 输出8
  // 让函数指针指向subtract函数
  operation = subtract;
  printf("减法结果: %d\n", operation(5, 3));
  // 输出2
  return 0;
  }

  • 一切皆地址

    • 变量(数据)是以某个地址为起点的一段内存中所存储的值
    • 函数(算法)是以某个地址为起点的一段内存中所存储的一组机器语言指令

  • 直接调用与间接调用

    • 直接调用:通过函数名来调用函数，CPU通过函数名直接获得函数所在地址并开始执行→返回
    • 间接调用:通过函数指针来调用函数，CPU通过读取函数指针存储的值获得函数所在地址并开始执行→返回

  • Java中没有与委托相对应的功能实体

  • 委托的简单使用

    • Action委托
    • Func委托
    namespace DelegateExample
{
class Program
{
static void Main(string[] args)
{
Calculatator calculatator = new Calculatator();
//无参数委托
Action act = new Action(calculatator.Report);
//打印出来的都是一样的
act();
act.Invoke();
calculatator.Report();
//带参数的委托
Func<
int, int, int> func = new Func<
int, int, int>(calculatator.Add);
int a = 13;
int b = 10;
int z = func.Invoke(a, b);
Console.WriteLine(z);
Func<
int, int, int> func2 = new Func<
int, int, int>(calculatator.Sub);
int z1 = func2.Invoke(a, b);
Console.WriteLine(z1);
}
}
class Calculatator
{
public void Report()
{
Console.WriteLine("I have 3 Methods");
}
public int Add(int x, int y)
{
return x + y;
}
public int Sub(int x, int y)
{
return x - y;
}
}
}

2、委托的声明（自定义委托）

  • 委托是一种类(class)，类是数据类型所以委托也是一种数据类型
  • 它的声名方式与一般的类不同，主要是为了照顾可读性和C/C++传统
  • 注意声明委托的位置
    • 避免写错地方结果声明成嵌套类型
  • 委托与所封装的方法必需类型兼容

在这里插入图片描述

  • 返回值的数据类型一致
  • 参数列表在个数和数据类型上一致(参数名不需要一样)
namespace DelegateExample
{
public delegate int Calc(int x, int y);
class Program
{
static void Main(string[] args)
{
Calculatator calculatator = new Calculatator();
Calc calc1 = new Calc(calculatator.Add);
Calc calc2 = new Calc(calculatator.Sub);
Calc calc3 = new Calc(calculatator.mul);
Calc calc4 = new Calc(calculatator.Div);
int a = 10;
int b = 5;
int c = calc1.Invoke(a, b);
Console.WriteLine(c);
int c1 = calc2.Invoke(a, b);
Console.WriteLine(c1);
int c2 = calc3.Invoke(a, b);
Console.WriteLine(c2);
int c3 = calc4.Invoke(a, b);
Console.WriteLine(c3);
}
}
class Calculatator
{
public int Add(int x, int y)
{
return x + y;
}
public int Sub(int x, int y)
{
return x - y;
}
public int mul(int x, int y)
{
return x * y;
}
public int Div(int x, int y)
{
return x / y;
}
}
}

3、委托的使用

3.1 实例:把方法当作参数传给另一个方法

  • 正确使用1:模板方法，“借用”指定的外部方法来产生结果相当于“填空题”常位于代码中部委托有返回值
namespace DelegateExample
{
public delegate int Calc(int x, int y);
class Program
{
static void Main(string[] args)
{
ProductFactory productFactory = new ProductFactory();
WrapFactory wrapFactory = new WrapFactory();
Func<Product> func1 = new Func<Product>(productFactory.MakePizza);
  Func<Product> func2 = new Func<Product>(productFactory.MakeCare);
    Box box1 = wrapFactory.WarpProduct(func1);
    Box box2 = wrapFactory.WarpProduct(func2);
    Console.WriteLine(box1.Product.Name);
    Console.WriteLine(box2.Product.Name);
    }
    }
    class Product
    {
    public string Name {
    get;
    set;
    }
    }
    class Box
    {
    public Product Product {
    get;
    set;
    }
    }
    class WrapFactory
    ()
    {
    public Box WarpProduct(Func<Product> getProduct)
      {
      Box box = new Box();
      Product product = getProduct.Invoke();
      box.Product = product;
      return box;
      }
      }
      class ProductFactory
      ()
      {
      public Product MakePizza()
      {
      Product product = new Product();
      product.Name = "pizza";
      return product;
      }
      public Product MakeCare()
      {
      Product product = new Product();
      product.Name = "care";
      return product;
      }
      }
      }
  • 正确使用2:回调(callback)方法，调用指定的外部方法相当于”流水线”常位于代码末尾委托无返回值
namespace DelegateExample
{
public delegate int Calc(int x, int y);
class Program
{
static void Main(string[] args)
{
ProductFactory productFactory = new ProductFactory();
WrapFactory wrapFactory = new WrapFactory();
Func<Product> func1 = new Func<Product>(productFactory.MakePizza);
  Func<Product> func2 = new Func<Product>(productFactory.MakeCare);
    // 实例化一个日志类，进行价格大于50的时候，打印相关日志
    Logger logger = new Logger();
    Action<Product> Log = new Action<Product>(logger.Log);
      Box box1 = wrapFactory.WarpProduct(func1, Log);
      Box box2 = wrapFactory.WarpProduct(func2, Log);
      Console.WriteLine(box1.Product.Name);
      Console.WriteLine(box2.Product.Name);
      }
      }
      class Logger
      {
      public void Log(Product product)
      {
      Console.WriteLine("产品名：{0}，价格：{1}，创建于：{2}", product.Name, product.Price, DateTime.UtcNow);
      }
      }
      class Product
      {
      public string Name {
      get;
      set;
      }
      public decimal Price {
      get;
      set;
      }
      }
      class Box
      {
      public Product Product {
      get;
      set;
      }
      }
      class WrapFactory
      ()
      {
      public Box WarpProduct(Func<Product> getProduct, Action<Product> LogCallback)
        {
        Box box = new Box();
        Product product = getProduct.Invoke();
        if (product.Price >
        50)
        {
        LogCallback.Invoke(product);
        }
        box.Product = product;
        return box;
        }
        }
        class ProductFactory
        ()
        {
        public Product MakePizza()
        {
        Product product = new Product();
        product.Name = "pizza";
        product.Price = 10;
        return product;
        }
        public Product MakeCare()
        {
        Product product = new Product();
        product.Name = "care";
        product.Price = 100;
        return product;
        }
        }
        }

3.2 注意:难精通+易使用+功能强大东西，一旦被滥用则后果非常严重

  • 缺点1:这是一种方法级别的紧耦合，现实工作中要慎之又慎
  • 缺点2:使可读性下降、debug的难度增加
  • 缺点3:把委托回调、异步调用和多线程纠缠在一起，会让代码变得难以阅读和维护
  • 缺点4:委托使用不当有可能造成内存泄漏和程序性能下降

4、委托的高级使用

4.1 多播（multicast）委托

多播委托（Multicast Delegate） 是一种特殊的委托类型，它可以同时引用多个方法，当委托被调用时，会依次执行所有被引用的方法。这一特性使得多播委托成为实现事件机制、回调链等场景的核心基础。

多播委托通过将多个方法组合成一个可调用的实体，实现了 “一次调用，多方响应” 的效果，是 C# 中实现事件、回调等功能的核心机制。

namespace DelegateExample
{
public delegate int Calc(int x, int y);
class Program
{
static void Main(string[] args)
{
Student student = new Student() { Id = 1, Color = ConsoleColor.Gray
};
Student student1 = new Student() { Id = 2, Color = ConsoleColor.Red
};
Student student2 = new Student() { Id = 3, Color = ConsoleColor.Green
};
Action action1 = new Action(student.DoHomework);
Action action2 = new Action(student1.DoHomework);
Action action3 = new Action(student2.DoHomework);
Console.WriteLine("====================单播委托======================");
action1.Invoke();
action2.Invoke();
action3.Invoke();
Console.WriteLine("====================多播委托======================");
//多播委托
action1 += action2;
action1 += action3;
action1.Invoke();
}
}
class Student
{
public int Id {
get;
set;
}
public ConsoleColor Color {
get;
set;
}
public void DoHomework()
{
for (int i = 0; i <
5; i++)
{
Console.ForegroundColor = this.Color;
Console.WriteLine("Student {0} doing work {1} hour", this.Id, i);
}
}
}
}

打印结果，多个单播委托和多播委托打印结果一致；

在这里插入图片描述

4.2隐式异步调用

1. 同步与异步的简介

  • 中英文的语言差异
  • 同步:你做完了我(在你的基础上)接着做
  • 异步:咱们两个同时做(相当于汉语中的“同步进行”)

在这里插入图片描述

2.同步调用与异步调用的对比

  • 每一个运行的程序是一个进程(process)
  • 每个进程可以有一个或者多个线程(thread )
  • 同步调用是在同一线程内异步调用的底层机理是多线程。
  • 串行同步单线程，并行异步多线程

3. 隐式多线程 vs 显式多线程

  • 直接同步调用:使用方法名
  • 间接同步调用:使用单播/多播委托的Invoke方法
namespace DelegateExample
{
public delegate int Calc(int x, int y);
class Program
{
static void Main(string[] args)
{
Student student = new Student() { Id = 1, Color = ConsoleColor.Gray
};
Student student1 = new Student() { Id = 2, Color = ConsoleColor.Red
};
Student student2 = new Student() { Id = 3, Color = ConsoleColor.Green
};
//直接调用
student.DoHomework();
student1.DoHomework();
student2.DoHomework();
//单播委托间接调用
Action action1 = new Action(student.DoHomework);
Action action2 = new Action(student1.DoHomework);
Action action3 = new Action(student2.DoHomework);
action1.Invoke();
action2.Invoke();
action3.Invoke();
//多播委托间接调用
action1 += action2;
action1 += action3;
action1.Invoke();
for (int i = 0; i <
10; i++) {
Console.ForegroundColor = ConsoleColor.Cyan;
Console.WriteLine("Main thread {0}", i);
}
}
}
class Student
{
public int Id {
get;
set;
}
public ConsoleColor Color {
get;
set;
}
public void DoHomework()
{
for (int i = 0; i <
5; i++)
{
Console.ForegroundColor = this.Color;
Console.WriteLine("Student {0} doing work {1} hour", this.Id, i);
}
}
}
}

打印结果均相同

在这里插入图片描述

  • 隐式异步调用:使用委托的BeginInvoke
namespace DelegateExample
{
public delegate int Calc(int x, int y);
class Program
{
static void Main(string[] args)
{
Student student = new Student() { Id = 1, Color = ConsoleColor.Gray
};
Student student1 = new Student() { Id = 2, Color = ConsoleColor.Red
};
Student student2 = new Student() { Id = 3, Color = ConsoleColor.Green
};
Action action1 = new Action(student.DoHomework);
Action action2 = new Action(student1.DoHomework);
Action action3 = new Action(student2.DoHomework);
//.NET 5 及更高版本Action.BeginInvoke 受到了限制
action1.BeginInvoke(null, null);
action2.BeginInvoke(null, null);
action3.BeginInvoke(null, null);
for (int i = 0; i <
10; i++) {
Console.ForegroundColor = ConsoleColor.Cyan;
Console.WriteLine("Main thread {0}", i);
}
}
}
class Student
{
public int Id {
get;
set;
}
public ConsoleColor Color {
get;
set;
}
public void DoHomework()
{
for (int i = 0; i <
5; i++)
{
Console.ForegroundColor = this.Color;
Console.WriteLine("Student {0} doing work {1} hour", this.Id, i);
}
}
}
}
  • 显式导步调用:使用Thread
using System.Threading;
namespace DelegateExample
{
public delegate int Calc(int x, int y);
class Program
{
static void Main(string[] args)
{
Student student = new Student() { Id = 1, Color = ConsoleColor.Gray
};
Student student1 = new Student() { Id = 2, Color = ConsoleColor.Red
};
Student student2 = new Student() { Id = 3, Color = ConsoleColor.Green
};
Thread thread1 = new Thread(new ThreadStart(student.DoHomework));
Thread thread2 = new Thread(new ThreadStart(student1.DoHomework));
Thread thread3 = new Thread(new ThreadStart(student2.DoHomework));
thread1.Start();
thread2.Start();
thread3.Start();
for (int i = 0; i <
10; i++)
{
Console.ForegroundColor = ConsoleColor.Cyan;
Console.WriteLine("Main thread {0}", i);
}
}
}
class Student
{
public int Id {
get;
set;
}
public ConsoleColor Color {
get;
set;
}
public void DoHomework()
{
for (int i = 0; i <
5; i++)
{
Console.ForegroundColor = this.Color;
Console.WriteLine("Student {0} doing work {1} hour", this.Id, i);
}
}
}
}

打印结果：异步调用

在这里插入图片描述

  • Task 异步调用
using System.Threading;
using System.Threading.Tasks;
namespace DelegateExample
{
public delegate int Calc(int x, int y);
class Program
{
static void Main(string[] args)
{
Student student = new Student() { Id = 1, Color = ConsoleColor.Gray
};
Student student1 = new Student() { Id = 2, Color = ConsoleColor.Red
};
Student student2 = new Student() { Id = 3, Color = ConsoleColor.Green
};
Task task1 = new Task(student.DoHomework);
Task task2 = new Task(student1.DoHomework);
Task task3 = new Task(student2.DoHomework);
task1.Start();
task2.Start();
task3.Start();
for (int i = 0; i <
10; i++)
{
Console.ForegroundColor = ConsoleColor.Cyan;
Console.WriteLine("Main thread {0}", i);
}
}
}
class Student
{
public int Id {
get;
set;
}
public ConsoleColor Color {
get;
set;
}
public void DoHomework()
{
for (int i = 0; i <
5; i++)
{
Console.ForegroundColor = this.Color;
Console.WriteLine("Student {0} doing work {1} hour", this.Id, i);
}
}
}
}

在这里插入图片描述

posted @ 2025-08-03 09:53  yfceshi  阅读(5)  评论(0)    收藏  举报