设计模式（3）工厂方法模式

模式介绍

Factory Method模式是一个Creation模式，它定义了用于创建对象的接口，但是没有指定该接口的各个实现将实例化什么对象。

这意味着，当使用这个模式时，您可以定义对象的某些方法和属性，这些方法和属性对于使用Factory方法创建的所有对象都是通用的，但是让各个Factory方法定义它们将实例化的特定对象。

示例

我们还是使用三明治举例子

三明治组成抽象类

/// <summary>
/// Product
/// </summary>
abstract class Ingredient { }

三明治组成具体类

/// <summary>
/// Concrete Product
/// </summary>
class Bread : Ingredient { }

/// <summary>
/// Concrete Product
/// </summary>
class Turkey : Ingredient { }

/// <summary>
/// Concrete Product
/// </summary>
class Lettuce : Ingredient { }

/// <summary>
/// Concrete Product
/// </summary>
class Mayonnaise : Ingredient { }

创建三明治的抽象类

/// <summary>
/// Creator
/// </summary>
abstract class Sandwich
{
    private List<Ingredient> _ingredients = new List<Ingredient>();

    public Sandwich()
    {
        CreateIngredients();
    }

    //Factory method
    public abstract void CreateIngredients();

    public List<Ingredient> Ingredients
    {
        get { return _ingredients; }
    }
}

创建三明治的具体类
（下面那个是个超级三明治...）

/// <summary>
/// Concrete Creator
/// </summary>
class TurkeySandwich : Sandwich
{
    public override void CreateIngredients()
    {
        Ingredients.Add(new Bread());
        Ingredients.Add(new Mayonnaise());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Bread());
    }
}

/// <summary>
/// Concrete Creator
/// </summary>
class Dagwood : Sandwich
{
    public override void CreateIngredients()
    {
        Ingredients.Add(new Bread());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Mayonnaise());
        Ingredients.Add(new Bread());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Mayonnaise());
        Ingredients.Add(new Bread());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Mayonnaise());
        Ingredients.Add(new Bread());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Mayonnaise());
        Ingredients.Add(new Bread());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Mayonnaise());
        Ingredients.Add(new Bread());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Turkey());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Lettuce());
        Ingredients.Add(new Mayonnaise());
        Ingredients.Add(new Bread());
    }
}

客户端调用

class Program
{
    static void Main(string[] args)
    {
        var turkeySandwich = new TurkeySandwich();
        var dagwood = new Dagwood();
        //Do something with these sandwiches (like, say, eat them).
        ...
    }
}

总结

Factory Method模式提供了一种可以实例化对象的方式，但是创建这些实例的细节由实例类自己定义。

源代码

https://github.com/exceptionnotfound/DesignPatterns/tree/master/FactoryMethodPattern

原文

https://www.exceptionnotfound.net/the-daily-design-pattern-factory-method/