工厂模式

实践/后端/项目/工厂模式.md

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+>简单工厂
+- 简单/简易工厂并不是一个设计模式, 更多是一个编程习惯. 但是使用的非常广泛.
+- 例如披萨店的实例
+![](./imgs/简单工厂.png)
+
+> 用C#/.net core实现简单工厂
+- Pizza的父类
+```
+using System;
+using System.Collections.Generic;
+
+namespace SimpleFactory.Pizzas
+{
+    public abstract class Pizza
+    {
+        public string Name { get; protected set; }
+        public string Dough { get; protected set; }
+        public string Sauce { get; protected set; }
+        protected List<string> Toppings = new List<string>();
+
+        public void Prepare()
+        {
+            Console.WriteLine($"Preparing: {Name}");
+            Console.WriteLine($"Tossing: {Dough}");
+            Console.WriteLine($"Adding sauce: {Sauce}");
+            Console.WriteLine("Adding toppings: ");
+            Toppings.ForEach(x => Console.WriteLine($"  {x}"));
+        }
+
+        public void Bake()
+        {
+            Console.WriteLine("Bake for 25 minutes");
+        }
+
+        public void Cut()
+        {
+            Console.WriteLine("Cutting the pizza into diagnol slices");
+        }
+
+        public void Box()
+        {
+            Console.WriteLine("Placing pizza in official PizzaStore box......");
+        }
+    }
+}
+```
+- 各种Pizza
+```
+namespace SimpleFactory.Pizzas
+{
+    public class CheesePizza: Pizza
+    {
+        public CheesePizza()
+        {
+            Name = "Cheese Pizza";
+            Dough = "Think Dough";
+            Sauce = "Salad";
+            Toppings.Add("Grated Reggiano Cheese");
+        }
+    }
+}
+
+namespace SimpleFactory.Pizzas
+{
+    public class ClamPizza: Pizza
+    {
+        public ClamPizza()
+        {
+            Name = "Clam Pizza";
+            Sauce = "Tomato sauce";
+            Dough = "Soft dough";
+            Toppings.Add("Shrimp meat");
+        }
+    }
+}
+
+namespace SimpleFactory.Pizzas
+{
+    public class PepperoniPizza: Pizza
+    {
+        public PepperoniPizza()
+        {
+            Name = "Pepperoni Pizza";
+            Dough = "Thin dough";
+            Sauce = "Black pepper";
+            Toppings.Add("Beef Granules");
+            Toppings.Add("Niblet");
+        }
+    }
+}
+```
+- 简单工厂
+```
+using SimpleFactory.Pizzas;
+
+namespace SimpleFactory
+{
+    public class SimplePizzaFactory
+    {
+        public Pizza CreatePizza(string type)
+        {
+            Pizza pizza = null;
+            switch (type)
+            {
+                case "cheese":
+                    pizza = new CheesePizza();
+                    break;
+                case "pepperoni":
+                    pizza = new PepperoniPizza();
+                    break;
+                case "clam":
+                    pizza = new ClamPizza();
+                    break;
+            }
+
+            return pizza;
+        }
+    }
+}
+```
+- PizzaStore
+```
+using SimpleFactory.Pizzas;
+
+namespace SimpleFactory
+{
+    public class PizzaStore
+    {
+        private readonly SimplePizzaFactory _factory;
+
+        public PizzaStore(SimplePizzaFactory factory)
+        {
+            _factory = factory;
+        }
+
+        public Pizza OrderPizza(string type)
+        {
+            var pizza = _factory.CreatePizza(type);
+            pizza.Prepare();
+            pizza.Bake();
+            pizza.Cut();
+            pizza.Box();
+            return pizza;
+        }
+    }
+}
+```
+
+> 工厂方法模式
+
+- 工厂方法模式定义了一个创建对象的接口, 但是让子类来决定具体创建的是哪一个对象. 工厂方法让一个类延迟实例化, 直到子类的出现.
+- ![](./imgs/工厂方法模式.png)
+
+> 设计原则
+- DIP (Dependency Inversion Principle) 依赖反转原则.
+- 进一步解释就是: 高级别的组件不应该依赖于低级别的组件, 它们都应该依赖于抽线.