【C#】委托

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委托

委托（delegate）是一种类型，定义了一种方法签名，因此可以将方法作为参数进行传递。
委托类似于 C++ 中的函数指针，但比函数指针更加安全和灵活。
使用委托，可以实现事件处理、回调函数等功能。
建议：使用接口取代委托

• Action
  • 无参无返回
• Func
  • 有参有返回

        Calaculator calaculator = new Calaculator();// Actionnew Action(calaculator.Report).Invoke();// FuncFunc<int, int, int> func1 = new Func<int, int, int>(calaculator.Add);Func<int, int, int> func2 = new Func<int, int, int>(calaculator.Sub);int x = 100;int y = 200;int z = 0;// 可以省略invokez = func1(x, y);Console.WriteLine(z);z = func2.Invoke(x, y);Console.WriteLine(z);class Calaculator {public void Report(){Console.WriteLine("i have 3 methods");}public int Add(int a, int b){return a + b;}public int Sub(int a, int b){return a - b;}
}

自定义委托

// 与类平级，放到类中属于嵌套
public delegate double Calc(double x,double y);
internal class Program
{static void Main(string[] args){Calaculator calaculator = new Calaculator();Calc calc1 = new Calc(calaculator.Add1);Calc calc2 = new Calc(calaculator.Mul);double x = 100;double y = 100;double z = 0;z = calc1.Invoke(x, y);Console.WriteLine(z);z = calc2.Invoke(x, y);Console.WriteLine(z);}
}

模板方法（工厂模式

”借用“指定的外部方法来产生结果 ， 提高对代码的复用
ProductFactory() 只需要扩展这个方法，其他方法都不用动

    static void Main(string[] args){ProductFactory productFactory = new ProductFactory();WrapFactory wrapFactory = new WrapFactory();Func<Product> func1 = new Func<Product>(productFactory.MakeToy);Func<Product> func2 = new Func<Product>(productFactory.MakePizza);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) {Box box = new Box();// invoke 执行拿到产品（不用管是什么产品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 MakeToy() {Product product = new Product();product.Name = "Toy";return product;}
}

回调(callback)函数（观察者模式

调用指定的外部方法
在模板方法基础上添加

internal class Program
{static void Main(string[] args){ProductFactory productFactory = new ProductFactory();WrapFactory wrapFactory = new WrapFactory();Func<Product> func1 = new Func<Product>(productFactory.MakeToy);Func<Product> func2 = new Func<Product>(productFactory.MakePizza);Logger logger = new Logger();Action<Product> action = new Action<Product>(logger.Log);Box box1 = wrapFactory.WrapProduct(func1,action);Box box2 = wrapFactory.WrapProduct(func2,action);Console.WriteLine(box1.Product.Name);Console.WriteLine(box2.Product.Name);}
}class Logger {public void Log(Product product) {//DateTime.UtcNow 无时区时间 ; DateTime.Now 有时区Console.WriteLine("Product '{0}' created at {1}.Price is {2}",product.Name,DateTime.UtcNow,product.Price);}
}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) {Box box = new Box();Product product = getProduct.Invoke();// 回调函数：触发某种条件就自动执行if (product.Price >= 50) {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 MakeToy() {Product product = new Product();product.Name = "Toy";product.Price=120;return product;}
}

多播（multicast）委托

委托的高级使用

使用接口 重构 模板方法代码

直接用接口，不使用委托。

方法形参为接口，类继承接口，new不同的类传进同个方法

internal class Program
{static void Main(string[] args){WrapFactory wrapFactory = new WrapFactory();Logger logger = new Logger();Action<Product> action = new Action<Product>(logger.Log);Box box1 = wrapFactory.WrapProduct(new PizzaFactory());Box box2 = wrapFactory.WrapProduct(new ToyCarFactory());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 ToyCarFactory : IProductFactory
{public Product Make(){Product product = new Product();product.Name = "Toy";product.Price = 120;return product;}
}
class WrapFactory {public Box WrapProduct(IProductFactory productFactory) {Box box = new Box();Product product = productFactory.Make();box.Product = product;return box;}
}
}

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注意

委托：

参考

刘铁猛——C#