Factory Design Pattern

Today I will show how to implement factory design pattern in NET platform.
One type of pattern that we see again and again in OO programs is the Factory pattern.
A Factory pattern is one that returns an instance of one of several possible classes, depending on the data provided to it.
Consider the following C# code sample:

using System;
using System.Runtime.Remoting;
namespace Factory
{
/// /// implements factory design pattern ///
public static class WorkerFactory
{
  private static string _asmName = "MyAssembly.";

  //returns new worker object
  public static void CreateWorker(out MyType mytypeobject, string strtype) // this method takes 2 arguments: 1-st for the object you want to instantiate and the second one for type name.
  {
   MyType sys = null;
   mytypeobject = null;
   string fullname = _asmName+strtype;
   try {
     ObjectHandle handle = System.Activator.CreateInstance(_asmName, fullname); //this method takes assembly name and type name to create an instance of the object
     MyType sys = (MyType)handle.Unwrap(); //You need to cast it to particular kind of the object
    }
    catch
    {
     throw new ApplicationException("Worker Factory can not create and object from assembly "+_asmName+" with name "+ns+".");
    }
    finally
    {
     if(sys != null) mytypeobject = sys;
    }
   }
  }
}

Feedback

# re: Factory Design Pattern

I'm afraid that everything I've read thus far on your blog is far from ideal.

One of the most important facets of a factory is that you have a known contract that grantees that a concrete class must implement. Without it, you could get anything back from a call to System.Activator.CreateInstance();

At minimum, the following are required:

1) An interface to define your contract
2) A concrete class (or classes) that implement your interface
3) A factory method that returns a concrete class that implements your interface
4) A consumer that [through the factory method] requests an object of the same type defined by the interface.

Your approach will fail miserably when Actavator.CreateInstance() returns something that you weren't ready to have returned.

You're better off using the following approach: http://www.dofactory.com/patterns/patternfactory.aspx 9/9/2009 12:30 PM | DJ Jazzy Jeff & the Fresh Prince

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