设计模式 - 6) 工厂模式

前面讲到的简单工厂如下面这段代码，后续需要拓展功能时，需要在简单工厂里面添加 case ，这依旧违反了开放-封闭中的对修改关闭的原则。

// 工厂生成对象类
public class OperationFactory
{
    public static OperationClass GetOperation(string operationType)
    {
        OperationClass opera = null;
        switch (operationType)
        {
            case "+":
                opera = new AddOperation();
                break;
            case "-":
                opera = new SubOperation();
                break;
            case "*":
                opera = new MulOperation();
                break;
            case "/":
                opera = new DivOperation();
                break;
            case "sqrt":
                opera = new SqrtOperation();
                break;
            case "squa":
                opera = new SquareOperation();
                break;
            default:
                 break;
        }
        return opera;
    }
}

一、将一个雷锋的简单工厂修改成工厂模式

1. 简单工厂实现代码

public class LeiFeng
{
    public void Sweep()
    {
        Console.WriteLine("扫地");
    }

    public void Wash()
    {
        Console.WriteLine("洗衣");
    }

    public void BuyRice()
    {
        Console.WriteLine("买米");
    }
}

public class Undergraduate : LeiFeng { }

public class Volunteer : LeiFeng { }

public class SimpleFactory
{
    public static LeiFeng CreateLeiFeng(string type)
    {
        LeiFeng result = null;
        switch (type)
        {
            case "big student":
                result = new Undergraduate();
                break;
            case "volunteer":
                result = new Volunteer();
                break;
            default:
                break;
        }
        return result;
    }
}

LeiFeng studentA = SimpleFactory.CreateLeiFeng("big student");
studentA.Sweep();
LeiFeng studentB = SimpleFactory.CreateLeiFeng("big student");
studentB.Wash();
LeiFeng studentC = SimpleFactory.CreateLeiFeng("big student");
studentC.BuyRice();

2. 工厂模式实现代码

结构是这样的

sequenceDiagram Creator->>Product: 创造生产者 ConcreteCreator->>ConcreteProduct: 工厂创造生产者 ConcreteCreator->>Creator: 继承 ConcreteProduct->>Product: 继承

public interface IFactory
{
    LeiFeng CreateLeiFeng();
}

public class UndergraduateFactory : IFactory
{
    public LeiFeng CreateLeiFeng()
    {
        return new Undergraduate();   
    }
}

public class VolunteerFactory : IFactory
{
    public LeiFeng CreateLeiFeng()
    {
        return new Volunteer();
    }
}
    
IFactory factory = new UndergraduateFactory();
LeiFeng lf = factory.CreateLeiFeng();
lf.Sweep();
lf.Wash();
lf.BuyRice();  

后面要改只需要改第一行：IFactory factory = new UndergraduateFactory();

3. 你可能会说，那工厂其实没什么作用，直接一句不就可以了：

LeiFeng lf = new Undergraduate();

结构如下

graph LR ConcreteProduct--继承-->Product

这不够规范，而且工厂模式可以结合单例模式。