C艹——委托

C艹——委托

什么是委托

委托（delegate）是函数指针的升级版

·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储存的值、
函数（算法）是以某个地址为起点的一段内存中所储存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通过读取指针存储的值获得函数所在地址并开始执行→返回

·Java中并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

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace ConsoleApp33
{class Program{static void Main(string[] args){Calculator calculator = new Calculator();Action action = new Action(calculator.Report);///只需要Report方法名，不需要调用这个函数所以后面不加（）。此时action已经指向calculator.Report这个方法calculator.Report();///直接调用action.Invoke();///间接调用action();///简单写法Func<int, int, int> func1 = new Func<int, int, int>(calculator.Add);Func<int, int, int> func2 = new Func<int, int, int>(calculator.Sub);int x = 100;int y = 200;int z = 0;z = func1.Invoke(x, y);Console.WriteLine(z);z = func2.Invoke(x, y);Console.WriteLine(z);}}class Calculator{public void Report(){Console.WriteLine("I have 3 methods.");}public int Add(int a,int b){int result = a + b;return result;}public int Sub(int a ,int b){int result = a - b;return result;}}
}

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数据类型
·它的声明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
避免写错地方声明成嵌套类型
·委托与所封装的方法必须“类型兼容”
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（参数名不需要相同）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace ConsoleApp34
{public delegate double Calc(double x, double y);///委托作为一个类，单独声明。当然也可以声明在类里面做为一个嵌套类class Program{static void Main(string[] args){Calculator calculator = new Calculator();Calc calc1 = new Calc(calculator.Add);Calc calc2 = new Calc(calculator.Sub);Calc calc3 = new Calc(calculator.Mul);Calc calc4 = new Calc(calculator.Div);double x = 100;double y = 200;double z = 0;z = calc1.Invoke(x, y);Console.WriteLine(z);z = calc2.Invoke(x, y);Console.WriteLine(z);z = calc3.Invoke(x, y);Console.WriteLine(z);z = calc4.Invoke(x, y);Console.WriteLine(z);}}class Calculator{public double Add(double x, double y){return x + y;}public double Sub(double x, double y){return x - y;}public double Mul(double x, double y){return x * y;}public double Div(double x, double y){return x / y;}}
}

委托的一般使用

·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

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace ConsoleApp35
{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.MakeToyCar);Box box1 = wrapFactory.WrapProduct(func1);Box box2 = wrapFactory.WrapProduct(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 WrapProduct(Func<Product>getProduct)///模板方法{Box box = new Box();///准备一个BoxProduct product = getProduct.Invoke();///获取产品box.Product = product;///把产品装到盒子里return box;   ///返回Box  ///模板方法的优点///Product类、Box类、WrapFactory类都不用动，只需拓展ProductFactory的方法即可///这样就实现了Reuse,重复使用，也叫“复用”。代码的复用不但可以提高工作效率，还可以减少BUG的引入。良好的结构复用结构是优秀软件所追求的共同目标之一。}}class ProductFactory{public Product MakePizza(){Product product = new Product();product.Name = "pizza";return product;}public Product MakeToyCar(){Product product = new Product();product.Name = "Toy car";return product;}}}
}

正确使用2：回调（call back）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

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace ConsoleApp35
{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.MakeToyCar);Logger logger = new Logger();Action<Product> log = new Action<Product>(logger.Log); Box box1 = wrapFactory.WrapProduct(func1,log);Box box2 = wrapFactory.WrapProduct(func2,log);Console.WriteLine(box1.Product.Name);Console.WriteLine(box2.Product.Name);}class  Logger//记录程序的运行状态，一般没有返回值{public void Log(Product product){Console.WriteLine("Product'{0}'created at {1}.Price is {2}.",product.Name,DateTime.UtcNow,product.Price);///存入数据库得用不带时区的时间，所以应该用UtcNow}}class Product{public string Name { get; set; }public double Price { get; set; }}class Box{public Product Product { get; set; }}class WrapFactory{public Box WrapProduct(Func<Product>getProduct,Action<Product>logCallBack)///不带返回值的方法用Action，Log接受一个Prodduct类型的参数{Box box = new Box();Product product = getProduct.Invoke();if (product.Price>=50)///回调方法就像打电话，需要你的时候就给你打电话，不需要就不打{logCallBack(product);}box.Product = product;return box;  }}class ProductFactory{public Product MakePizza(){Product product = new Product();product.Name = "pizza";product.Price = 12;return product;}public Product MakeToyCar(){Product product = new Product();product.Name = "Toy car";product.Price = 100;return product;}}}
}

小结：

·无论是模板方法还是回调方法他们的本质都是一样的。都是用委托类型的参数，封装一个外部的方法，然后把这个方法传进方法内部，再进行间接调用。

注意:难精通+易使用+功能强大的东西，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

委托的高级使用

·单播委托

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;namespace ConsoleApp36
{class Program{static void Main(string[] args){Student stu1 = new Student() { ID = 1, PenColor = ConsoleColor.Yellow };Student stu2 = new Student() { ID = 2, PenColor = ConsoleColor.Green };Student stu3 = new Student() { ID = 3, PenColor = ConsoleColor.Red };Action action1 = new Action(stu1.DoHomeWork);///一个委托封装一个方法的使用形式，单播委托Action action2 = new Action(stu2.DoHomeWork);Action action3 = new Action(stu3.DoHomeWork);action1.Invoke();action2.Invoke();action3.Invoke();}}
}class Student
{public int ID { get; set; }public ConsoleColor PenColor { get; set; }public void DoHomeWork(){for (int i = 0; i < 6; i++){Console.ForegroundColor = this.PenColor;Console.WriteLine("Student{0}doing homework {1}  hour(s)", this.ID, i);Thread.Sleep(1000);///1000毫秒=1秒，这个意思是无论你在哪个线程调用Thread.sleep(1000),这个线程就睡上一秒钟}}
}

·多播（multicast）委托（同步调用）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;namespace ConsoleApp36
{class Program{static void Main(string[] args){Student stu1 = new Student() { ID = 1, PenColor = ConsoleColor.Yellow };Student stu2 = new Student() { ID = 2, PenColor = ConsoleColor.Green };Student stu3 = new Student() { ID = 3, PenColor = ConsoleColor.Red };Action action1 = new Action(stu1.DoHomeWork);Action action2 = new Action(stu2.DoHomeWork);Action action3 = new Action(stu3.DoHomeWork);action1 += action3;///action2封装在action1里    action1 += action2;///action3也封装在action1里，action1里面封装了3个方法action1.Invoke();///像这种有个委托封装多种方法的就叫多播委托///执行顺序按照你的封装顺序执行}}
}class Student
{public int ID { get; set; }public ConsoleColor PenColor { get; set; }public void DoHomeWork(){for (int i = 0; i < 6; i++){Console.ForegroundColor = this.PenColor;Console.WriteLine("Student {0} doing homework {1}  hour(s)", this.ID, i);Thread.Sleep(1000);///1000毫秒=1秒，这个意思是无论你在哪个线程调用Thread.sleep(1000),这个线程就睡上一秒钟}}
}

`隐式异步调用

`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）

·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是多个线程（thread）
同步调用时在统一线程内

第一种同步调用

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;namespace ConsoleApp36
{class Program{static void Main(string[] args){Student stu1 = new Student() { ID = 1, PenColor = ConsoleColor.Yellow };Student stu2 = new Student() { ID = 2, PenColor = ConsoleColor.Green };Student stu3 = new Student() { ID = 3, PenColor = ConsoleColor.Red };stu1.DoHomeWork();///调用方法stu2.DoHomeWork();stu3.DoHomeWork();///调用完毕以后主线程还有事情要做，典型的同步调用for (int i = 0; i < 10; i++){Console.ForegroundColor = ConsoleColor.Cyan;Console.WriteLine("Main thread {0}.", i);Thread.Sleep(1000);}}}
}class Student
{public int ID { get; set; }public ConsoleColor PenColor { get; set; } public void DoHomeWork(){for (int i = 0; i < 6; i++){Console.ForegroundColor = this.PenColor;Console.WriteLine("Student {0} doing homework {1}  hour(s)", this.ID, i);Thread.Sleep(1000);///1000毫秒=1秒，这个意思是无论你在哪个线程调用Thread.sleep(1000),这个线程就睡上一秒钟}}
}

第二种同步调用

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;namespace ConsoleApp36
{class Program{static void Main(string[] args){Student stu1 = new Student() { ID = 1, PenColor = ConsoleColor.Yellow };Student stu2 = new Student() { ID = 2, PenColor = ConsoleColor.Green };Student stu3 = new Student() { ID = 3, PenColor = ConsoleColor.Red };Action action1 = new Action(stu1.DoHomeWork);Action action2 = new Action(stu2.DoHomeWork);Action action3 = new Action(stu3.DoHomeWork);action1.Invoke();action2.Invoke();action3.Invoke();///单播间接同步调用////*action1 += action2;action1 += action3;///多播间接同步调用*/for (int i = 0; i < 10; i++){Console.ForegroundColor = ConsoleColor.Cyan;Console.WriteLine("Main thread {0}.", i);Thread.Sleep(1000);}}}
}class Student
{public int ID { get; set; }public ConsoleColor PenColor { get; set; } public void DoHomeWork(){for (int i = 0; i < 6; i++){Console.ForegroundColor = this.PenColor;Console.WriteLine("Student {0} doing homework {1}  hour(s)", this.ID, i);Thread.Sleep(1000);///1000毫秒=1秒，这个意思是无论你在哪个线程调用Thread.sleep(1000),这个线程就睡上一秒钟}}
}

异步调用的底层机理是多线程（线程互不相干）


隐式异步调用

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;namespace ConsoleApp36
{class Program{static void Main(string[] args){Student stu1 = new Student() { ID = 1, PenColor = ConsoleColor.Yellow };Student stu2 = new Student() { ID = 2, PenColor = ConsoleColor.Green };Student stu3 = new Student() { ID = 3, PenColor = ConsoleColor.Red };Action action1 = new Action(stu1.DoHomeWork);Action action2 = new Action(stu2.DoHomeWork);Action action3 = new Action(stu3.DoHomeWork);action1.BeginInvoke(null,null);///异步隐式调用，BeginInvoke会自动创建一个分支线程帮我们调用封装的方法，括号两个参数关于后续操作，不需要，所以填nullaction2.BeginInvoke(null, null);//属于委托的隐式异步调用action3.BeginInvoke(null, null);for (int i = 0; i < 10; i++){Console.ForegroundColor = ConsoleColor.Cyan;Console.WriteLine("Main thread {0}.", i);Thread.Sleep(1000);}Console.ReadLine();}}
}class Student
{public int ID { get; set; }public ConsoleColor PenColor { get; set; } public void DoHomeWork(){for (int i = 0; i < 6; i++){Console.ForegroundColor = this.PenColor;Console.WriteLine("Student {0} doing homework {1}  hour(s)", this.ID, i);Thread.Sleep(1000);///1000毫秒=1秒，这个意思是无论你在哪个线程调用Thread.sleep(1000),这个线程就睡上一秒钟}}
}

执行结果

显示异步调用（比较古老的方法）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;namespace ConsoleApp36
{class Program{static void Main(string[] args){Student stu1 = new Student() { ID = 1, PenColor = ConsoleColor.Yellow };Student stu2 = new Student() { ID = 2, PenColor = ConsoleColor.Green };Student stu3 = new Student() { ID = 3, PenColor = ConsoleColor.Red };Thread thread1 = new Thread(new ThreadStart(stu1.DoHomeWork));Thread thread2 = new Thread(new ThreadStart(stu2.DoHomeWork));Thread thread3 = new Thread(new ThreadStart(stu3 .DoHomeWork));thread1.Start();thread2.Start();thread3.Start();for (int i = 0; i < 10; i++){Console.ForegroundColor = ConsoleColor.Cyan;Console.WriteLine("Main thread {0}.", i);Thread.Sleep(1000);}Console.ReadLine();}}
}class Student
{public int ID { get; set; }public ConsoleColor PenColor { get; set; } public void DoHomeWork(){for (int i = 0; i < 6; i++){Console.ForegroundColor = this.PenColor;Console.WriteLine("Student {0} doing homework {1}  hour(s)", this.ID, i);Thread.Sleep(1000);///1000毫秒=1秒，这个意思是无论你在哪个线程调用Thread.sleep(1000),这个线程就睡上一秒钟}}
}

执行结果

显示异步调用（更高级的方法）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;namespace ConsoleApp36
{class Program{static void Main(string[] args){Student stu1 = new Student() { ID = 1, PenColor = ConsoleColor.Yellow };Student stu2 = new Student() { ID = 2, PenColor = ConsoleColor.Green };Student stu3 = new Student() { ID = 3, PenColor = ConsoleColor.Red };Task task1 = new Task(new Action(stu1.DoHomeWork));Task task2 = new Task(new Action(stu2.DoHomeWork));Task task3 = new Task(new Action(stu3 .DoHomeWork));task1.Start();task2.Start();task3.Start();for (int i = 0; i < 10; i++){Console.ForegroundColor = ConsoleColor.Cyan;Console.WriteLine("Main thread {0}.", i);Thread.Sleep(1000);}Console.ReadLine();}}
}class Student
{public int ID { get; set; }public ConsoleColor PenColor { get; set; } public void DoHomeWork(){for (int i = 0; i < 6; i++){Console.ForegroundColor = this.PenColor;Console.WriteLine("Student {0} doing homework {1}  hour(s)", this.ID, i);Thread.Sleep(1000);///1000毫秒=1秒，这个意思是无论你在哪个线程调用Thread.sleep(1000),这个线程就睡上一秒钟}}
}

执行结果

串行同步单线程，并行同步多线程

·隐式多线程 v.s. 显示多线程
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
隐式异步调用：使用委托的BeginInvoke
显示异步调用：使用Thread或Task

`应该适时的使用一些接口（ interface）取代一些对委托的使用

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace ConsoleApp35
{class Program{static void Main(string[] args){IProductFactory pizzaFactory = new PizzaFactory();IProductFactory toyCarFactory = new ToyCarFortory();WrapFactory wrapFactory = new WrapFactory();Logger logger = new Logger();Action<Product> log = new Action<Product>(logger.Log);Box box1 = wrapFactory.WrapProduct(pizzaFactory, log);Box box2 = wrapFactory.WrapProduct(toyCarFactory, log);Console.WriteLine(box1.Product.Name);Console.WriteLine(box2.Product.Name);}interface IProductFactory{Product Make();}class PizzaFactory : IProductFactory{public Product Make(){Product product = new Product();product.Name = "pizza";product.Price = 12;return product;}}class ToyCarFortory : IProductFactory{public Product Make(){Product product = new Product();product.Name = "Toy car";product.Price = 100;return product;}}class Logger{public void Log(Product product){Console.WriteLine("Product'{0}'created at {1}.Price is {2}.", product.Name, DateTime.UtcNow, product.Price);///存入数据库得用不带时区的时间，所以应该用UtcNow}}class Product{public string Name { get; set; }public double Price { get; set; }}class Box{public Product Product { get; set; }}class WrapFactory{public Box WrapProduct(IProductFactory productFactory, Action<Product> logCallBack)///不带返回值的方法用Action{Box box = new Box();Product product = productFactory.Make();if (product.Price >= 50){logCallBack(product);}box.Product = product;return box;}}}
}

java完全使用接口取代的委托的功能，即Java没有与C艹中委托相对应的功能实体

·