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委托

委托（delegate）是一種類型，定義了一種方法簽名，因此可以將方法作為參數進行傳遞。
委托類似于 C++ 中的函數指針，但比函數指針更加安全和靈活。
使用委托，可以實現事件處理、回調函數等功能。
建議：使用接口取代委托

• Action
  • 無參無返回
• Func
  • 有參有返回

        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;}
}

自定義委托

// 與類平級，放到類中屬于嵌套
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（工廠模式

”借用“指定的外部方法來產生結果 ， 提高對代碼的復用
ProductFactory() 只需要擴展這個方法，其他方法都不用動

    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 執行拿到產品（不用管是什么產品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;}
}

回調(callback)函數（觀察者模式

調用指定的外部方法
在模板方法基礎上添加

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 無時區時間 ; DateTime.Now 有時區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();// 回調函數：觸發某種條件就自動執行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

委托的高級使用

使用接口 重構 模板方法代碼

直接用接口，不使用委托。

方法形參為接口，類繼承接口，new不同的類傳進同個方法

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：

參考

劉鐵猛——C#