Unity学前C#:委托详解

一.什么是委托

字面意思就是:这件事情我不亲自去做,而是委托别人去做
C#中的委托有点类似c/c++中的函数指针,但是C#中的委托就可以看作是函数指针的升级版

以下是c/c++的函数指针实例

#include<bits/stdc++.h>
using namespace std;

int (*Cal)(int a, int b);
//或者用typedef int (*Cal)将Cal定义为一种数据类型
int Add(int x, int y)
{
	cout << "x+y=" << x + y << endl;
	return x + y;
}

int main()
{
	Cal = Add;//函数指针的调用
	int x = 100;
	int y = 100;
	int c = Cal(x, y);
	return 0;
}

 先理解一个概念:一切皆地址

在计算机中所有的程序以及数据的存储都是有地址可循的,计算机组成原理就解释了程序的执行过程(将程序中的一条一条指令写入连续的内存中,并且用第一条指令的地址来表示它),所以函数和数据的区别就是,函数是寻找函数的地址,而数据是寻找数据的地址

直接调用:通过函数名调用,CPU通过函数名直接找到函数所在的首地址,然后调用函数

间接调用：通过函数指针调用,CPU先通过函数指针找到函数所在的地址然后调用函数

二.C#中的委托

C#中自带的委托

Fun<>：代参数的委托,一共有17中定义

Action ：不带参数的委托

class Programme
{
    static void Main(string[] args)
    {
        Complex complex = new Complex();
        Action action = new Action(complex.PrintInfo);//注意这里只是要获得函数的地址名字所以不用加括号,加括号就是表示调用该函数了
        action();
        Func<int, int, int> fun = new Func<int, int, int>(complex.Add);
        int test;
        test = fun(1, 2);
        Console.WriteLine(test);
    }
}

class Complex
{
    public void PrintInfo()
    {
        Console.WriteLine("PrintInfo has been used");
    }

    public int Add(int x, int y)
    {
        return x + y;
    }
}

/*
 * 输出结果
 * PrintInfo has been used
    3
 */

 自定义委托

delegate关键字

从某种意义上来讲,委托也可以算是一种类,所以在定义的时候应该与类同一个级别,也就是写在命名空间下面

delegate int Cal(int x, int b);
class Programme
{
    static void Main(string[] args)
    {
        Cal add = new Cal(Calculate.ADD);
        Cal cut = new Cal(Calculate.Cut);
        Cal mutiply = new Cal(Calculate.Mutiply);
        Cal except= new Cal(Calculate.Except);
        int x = 100;
        int y = 200;
        try
        {
            Console.WriteLine(add(x, y));
            Console.WriteLine(cut(x, y));
            Console.WriteLine(mutiply(x, y));
            Console.WriteLine(except(x, 0));
        }
        catch(Exception ex)
        {
            Console.WriteLine(ex.Message);
        }
    }
}

class Calculate
{
    public static int ADD(int x,int y)
    {
        return x + y;
    }

    public static int Cut(int x,int y)
    {
        return x - y;
    }

    public static int Mutiply(int x,int y)
    {
        return x * y;
    }

    public static int Except(int x,int y)
    {
        if (y == 0)
            throw new Exception("y cannot be zero");
        return x / y;
    }
}

三.委托方法的应用 

 1.模板方法

便于函数重用,有利于减少bug,降低bug的修复成本

class Programme
{
    static void Main(string[] args)
    {
        ProductFactory factory = new ProductFactory();
        Func<Product> fun1 = factory.MakingPizza;
        Func<Product> fun2 = factory.MakingToycar;
        WarpFactory warpFactory = new WarpFactory();
        Console.WriteLine(warpFactory.WarpProduct(fun1).Product.Name);
        Console.WriteLine(warpFactory.WarpProduct(fun2).Product.Name);
    }
}

class Box
{
    public Product Product { get; set; }
}

class Product
{
    public string Name { get; set; }
}

class WarpFactory
{
    public Box WarpProduct(Func<Product> fun)
    {
        Product product =fun();//或者fun.invoke
        Box box = new Box();
        box.Product = product;
        return box;
    }
}

class ProductFactory
{
    public Product MakingToycar()
    {
        Product product = new Product();
        product.Name = "Toy car";
        return product;
    }

    public Product MakingPizza()
    {
        Product product = new Product();
        product.Name = "Pizza";
        return product;
    }
}
    

2.回调方法 

回调的理解:假如你是公司的老板,你收到了很多实习生投递的简历,但是你要根据你的需求在合适的实践选择相应的员工

   class Programme
   {
       static void Main(string[] args)
       {
           ProductFactory factory = new ProductFactory();
           Func<Product> fun1 = factory.MakingPizza;
           Func<Product> fun2 = factory.MakingToycar;
           WarpFactory warpFactory = new WarpFactory();
           Logger logger = new Logger();
           Action<Product> action = logger.logCallBack;
           Console.WriteLine(warpFactory.WarpProduct(fun1,action).Product.Name);
           Console.WriteLine(warpFactory.WarpProduct(fun2,action).Product.Name);
       }
   }

   class Logger
   {
       public void logCallBack(Product product)
       {
           Console.WriteLine("{0} has been warped at {1} and the price is {2}", product.Name, DateTime.UtcNow,product.Price);
       }
   }

   class Box
   {
       public Product Product { get; set; }
   }

   class Product
   {
       public string Name { get; set; }
       public double Price { get; set; }
   }

   class WarpFactory
   {
       public Box WarpProduct(Func<Product> fun,Action<Product> LoggerCallBack)
       {
           Product product =fun();//或者fun.invoke
           Box box = new Box();
           box.Product = product;
           if(product.Price>50)
           {
               LoggerCallBack(product);
           }
           return box;
       }
   }

   class ProductFactory
   {
       public Product MakingToycar()
       {
           Product product = new Product();
           product.Name = "Toy car";
           product.Price = 100;
           return product;
       }

       public Product MakingPizza()
       {
           Product product = new Product();
           product.Name = "Pizza";
           product.Price = 10;
           return product;
       }
   }

 总结:难精通+易使用,在使用的时候还是要三思

四.委托的高级使用

多播(multicast)委托

一个委托内封装着不止一个方法

执行的顺序就是按照封装的顺序执行方法

class Programme
{
    static void Main(string[] args)
    {
        Student stu1 = new Student() { ID = 1,Color = ConsoleColor.Red};
        Student stu2 = new Student() { ID = 2, Color = ConsoleColor.Green };
        Student stu3 = new Student() { ID = 3,Color = ConsoleColor.Blue};
        Action action = stu1.DoHomeWord;
        Action action2 = stu2.DoHomeWord;
        Action action3 = stu3.DoHomeWord;
        action += action2;
        action += action3;
        action();
        
    }
}

class Student
{
    public int ID { get; set; }
    public ConsoleColor Color { get; set; }
    public void DoHomeWord()
    {
        for(int i=0;i<5;i++)
        {
            Console.ForegroundColor = Color;
            Console.WriteLine("{0} is Do Homework {1}", ID, i);
            Thread.Sleep(1000);//多线程,就是所在的线程每次执行到这里都休息一秒
        }
    }
}

 隐式异步调用

同步:你做完了,我接着做,相当于是流水线

程序开始执行的时候都会有一个主线程,其余的都叫做分线程,上图红线的就是主线程 ，其他颜色的线代表方法,不难看出每个方法执行的顺序是依次进行的,所以叫同步

异步:两个人互不相干

 隐式异步调用

//将上述代码的action()改成如下代码即可显示为异步调用
action.BeginInvoke(null,null);
action2.BeginInvoke(null,null);
action3.BeginInvoke(null,null);

可以发现显示的颜色并不符合代码的要求:

因为多个线程都在抢占同一个资源,这样就会导致资源抢夺,所以解决的办法就是给线程加锁,这是以后的内容了 

显示异步调用 

Task task1 = new Task(stu1.DoHomeWord);
Task task2 = new Task(stu2.DoHomeWord);
Task task3 = new Task(stu3.DoHomeWord);
task1.Start();
task2.Start();
task3.Start();

Thread thread1 = new Thread(new ThreadStart(action));
Thread thread2 = new Thread(new ThreadStart(action2));
Thread thread3 = new Thread(new ThreadStart(action3));
thread1.Start();
thread2.Start();
thread3.Start();

也出现了和隐式一样的资源抢夺情况

 五.拓展:Interface

本来一位接口是一个知识点,后来发现和c++中的纯虚函数相似,

interface可以代替委托

class Programme
{
    static void Main(string[] args)
    {
        IProductFactory toy = new ToyFactory();
        IProductFactory pizza = new PizzaFactory();
        WarpFactory warpFactory = new WarpFactory();
        Console.WriteLine(warpFactory.WarpProduct(toy).Product.Name);
        Console.WriteLine(warpFactory.WarpProduct(pizza).Product.Name);
    }
}

interface IProductFactory
{
    Product Make();
}

class ToyFactory:IProductFactory
{
    public Product Make()
    {
        Product product = new Product() { Name = "Toy Car"};
        return product;
    }
}

class PizzaFactory:IProductFactory
{
    public Product Make()
    {
        Product product= new Product() { Name = "Pizza" };
        return product;
    }
}
class Box
{
    public Product Product { get; set; }
}

class Product
{
    public string Name { get; set; }
}

class WarpFactory
{
    public Box WarpProduct(IProductFactory ipf)
    {
        Product product = ipf.Make();//或者fun.invoke
        Box box = new Box();
        box.Product = product;
        return box;
    }
}

总结

 委托的使用要非常谨慎,所以在c#中可以合并Interface一并使用,java之所以在没有委托的情况下能发展就是用了Interface实现了委托的功能

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