设计模式-工厂模式｜默然的博客

简单工厂

简单工厂不是GoF 23种设计模式中的一员，但是比较常见。将产品抽象出一个接口或基类。然后通过传递不同参数生产不同对象。

class Program
{
    static void Main(string[] args)
    {
        //创建工厂
        BallFactory factory = new BallFactory();
        // 根据传入的不同参数，创建不同的产品
        factory.Create("football");
        factory.Create("basketball");
    }
}
public interface IBall { }
public class FootBall : IBall
{
    public FootBall() { Console.WriteLine("Create football"); }
}
public class Basketball : IBall
{
    public Basketball() { Console.WriteLine("Create basketball"); }
}

public class BallFactory
{
    public IBall Create(string ballType)
    {
        IBall result = null;

        if (ballType == "football")
            result = new FootBall();
        else if (ballType == "basketball")
            result = new Basketball();

        return result;
    }
}

问题

如果要新增一个产品排球(baseball)，那就要修改BallFactory这个类,增加一个else if判断，这样就违背了开放-封闭原则。那我们就可以将工厂抽离出来，需要什么样的球就去调用对用的工厂生产，这就是工厂模式了。

工厂模式

定义一个用于创建对象的接口(IFactory), 由其子类决定创建实例。工厂模式将类的实例化延迟到其子类中。

class Program
{
    static void Main(string[] args)
    {
        // basketball factory
        IFactory basketBallFactory = new BasketBallFactory();
        // create product
        IBall basketball = basketBallFactory.Create();

        // football factory
        IFactory footBallFactory = new FootBallFactory();
        IBall football = footBallFactory.Create();
    }
}
public interface IBall { }
public class FootBall : IBall
{
    public FootBall() { Console.WriteLine("Create football"); }
}
public class Basketball : IBall
{
    public Basketball() { Console.WriteLine("Create basketball"); }
}

public interface IFactory{ IBall Create(); }

public class BasketBallFactory : IFactory
{
    public IBall Create() { return new Basketball(); }
}
public class FootBallFactory : IFactory
{
    public IBall Create() { return new FootBall(); }
}

问题

如果产品更多呢？乒乓球，羽毛球…,总不能每增加一种球就新建一个工厂吧。这就可以将产品，工厂抽象出来：A工厂可以生产篮球，也可以生产排球，羽毛球等等，当然B工厂也可以。A,B工厂生产的各种球可能外观，耐用程度等属性不同，但是都可以用来打。这样根据不同的工厂去分别生产对应不同的产品。这就是抽象工厂。

抽象工厂

提供一个创建一系列相关或相互依赖对象的接口，而无须指定它们具体的类。

class Program
{
    static void Main(string[] args)
    {
        // basketball factory
        IFactory factoryA = new FactoryA();
        factoryA.CreateBasketball();
        factoryA.CreateFootBall();

        // football factory
        IFactory factoryB = new FactoryB();
        factoryB.CreateBasketball();
        factoryB.CreateFootBall();
    }
}


public interface IFootBall { }
public class FootBallA:IFootBall
{
    public FootBallA() { Console.WriteLine("Create football by A factory"); }
}
public class FootBallB : IFootBall
{
    public FootBallB() { Console.WriteLine("Create football by B factory"); }
}


public interface IBasketBall { }
public class BasketballA:IBasketBall
{
    public BasketballA() { Console.WriteLine("Create basketball by A Factory"); }
}
public class BasketballB : IBasketBall
{
    public BasketballB() { Console.WriteLine("Create basketball by B Factory"); }
}


public interface IFactory
{
    IBasketBall CreateBasketball();
    IFootBall CreateFootBall();
}
public class FactoryA : IFactory
{
    public IBasketBall CreateBasketball() { return new BasketballA(); }

    public IFootBall CreateFootBall() { return new FootBallA(); }
}
public class FactoryB : IFactory
{
    public IBasketBall CreateBasketball() { return new BasketballB(); }

    public IFootBall CreateFootBall() { return new FootBallB(); }
}

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