好的源代码可以使我在C＃上的工厂设计模式上有所作为

Question

I feel that I should start using the factory method design pattern on some of my code. Here is what I am doing;

The below code is my generator class for Accom namespace:

namespace Accom {

    public class Generator {

      int? _id;
      string _name;

      public Generator(int? id = null, string name = null) {
          _id = id;
          _name = name;
      }

      public string GetBaseUrl() { 

          //some logic sits here.

          return somestring;

      }

      //Can have some other methods as well

    }

}

I will have the same start-up for Traf namespace as well:

namespace Traf {
    public class Generator {
      int? _id;
      string _name;

      public Generator(int? id = null, string name = null) {
          _id = id;
          _name = name;
      }

      public string GetBaseUrl() { 
          //some logic sits here. Same one with the Accom.

          return somestring;
      }

      //Can have some other methods as well
    }
}

So, this will repeat again and again.

I tried to create some factory pattern for that but all of the abstract classes were mixed and I confused a lot (I think it is because this is first time I am trying to do something like that).

Can anyone help me on this and point me to good source code that I can read and get a sense from?

Answer 1

• Create an abstract class for generator
• create child class for different types of generator
• Make a factory class
• Make factory as singleton
• Create one method (Common) which will take parameter as string (with namespace if classes are in different namespace )
• Use reflection to create instance of different object in method common
• return base type from common
• Create different methods (A,B,C) for get different instance, call method (Common)
• cast the result from common to type u want to return

EDIT

public abstract class Generator
{
    public Generator(int? i, string name) { }
    public abstract string GetBaseUrl();
}

public class GeneratorA : Generator
{
    public GeneratorA(int? i, string name) : base(i, name) { }
}
public class GeneratorB : Generator
{
    public GeneratorB(int? i, string name) : base(i, name) { }
}
public class GeneratorFactory
{
    // Make singleton
    public GeneratorB GenerateB(int? i, string name)
    {
        return (GeneratorB)this.Generate(i, name, "GeneratorB");
    }

    public GeneratorA GenerateA(int? i, string name)
    {
        return (GeneratorA)this.Generate(i, name, "GeneratorA");
    }

    public Generator Generate(int? i, string name, string genType)
    {
        return new GeneratorA(); // use reflection to generate child generator based on string "genType"
    }
}

Answer 2

I think this code project article on the AbstractFactoryPattern does a pretty good job of providing a useful example.

However, unless you have a really good reason to, you should not create the same class in several different namespaces. You can always use using Accom; to access your Generator class from the Traf namespace.

---

Edit in response to comment that each Generator in a different namespace will have a different set of methods.

You can't use the abstract factory pattern if the implementations will have different methods. The idea of the abstract factory pattern is to create a common interface that all objects returned by the factory will implement, then use some context in the factory to choose the correct implementation for a given situation.

The advantage you gain by using a factory is called Inversion of Control . Basically, your client code does not depend on a particular implementation of the Generator class (by having a variable of that type, or by calling a constructor for it).

However, if you need to access methods that are specific to an implementation, then you can't access them through a common interface, which means you don't gain the Inversion of Control benefit, which means there is no real reason to use the abstract factory pattern.