•  
• Download FactoryPatternWithGenerics - 93.97 KB

Introduction

This article reveals some good use of design patterns using generics.Think if these design patterns are made using generics in .NET it can work as wonders. You can create your own design pattern class library which could be than made re-usable in any project. I will be showing Factory Design Pattern using generics in .NET.

Background

For those who don't know Factory Design Pattern please refer to this article of GOF available at below mentioned link :- http://www.dofactory.com/Patterns/PatternFactory.aspx

Using the Code

Now let's start with some coding stuff. First I will show you implementation of Factory pattern without using generics. Then we will go about changing the same factory pattern using generics and you will see the difference. So we start with creating two simple class i.e. ReportGenerator and ReportAnalyser which shares a common interface implementation IActivity.

NOTE :- I have taken ReportGenerator and ReportAnalyser classes for example purpose only.

    
    public interface IDBActivity 
    {
     void Process();
    }

    public class Enumeration
    {
        public enum ModuleName
        {
            ReportGenerator = 1,
            ReportAnalyser = 2
        }

    }

    		
    public class ReportGenerator : IActivity 
    {
      public void Process()
      {
        // Do some coding here ...
      }
						    						                            
    }

    public class ReportAnalyser : IActivity 
    {
      public void Process()
      {
         // Do some coding here ...
      }
						                                
    }
        
    

    public class FactoryClass
    {
      public static IActivity CreateInstance(Enumeration.ModuleName enumModuleName)
      {
         IActivity objActivity = null;
		
         switch (enumModuleName)
         {
              case Enumeration.ModuleName.ReportGenerator:
                     objActivity = new ReportGenerator(); 
                     break;
              case Enumeration.ModuleName.ReportAnalyser:
                     objActivity = new ReportAnalyser();
                     break;
              default:
                     break;
         }
         return objActivity;
      }
    }
    			        
    
    

    private void btnProcess_Click(object sender, EventArgs e)
    {	
      IActivity objActivity = null;

      objActivity = FactoryClass.CreateInstance(Enumeration.ModuleName.ReportGenerator);
      objActivity.Process();
    }	    	
    

  		
    public class FactoryPattern <K,T> 
        where T : class, K, new()
    {

        public static K CreateInstance()
        {
            K objK;

            objK = new T();

            return objK;            
        }
    }	
  	

You might be wondering what's all this ??? :-). Okay, I will explain you the concept. Here, I have created FactoryPattern class using generics. It takes two parameters i.e. "K" and "T". T parameter has "where" constraint which depicts that T should be a class, it should be inherited from K and it's instance can be created. Huh ... too much of conceptual. Let's analyze this line where T : class, K, new() :-

    public class FactoryClass
    {
      public static IActivity CreateInstance(Enumeration.ModuleName enumModuleName)
      {
         IActivity objActivity = null;
		
         switch (enumModuleName)
         {
              case Enumeration.ModuleName.ReportGenerator:
                     /* Old coding ...
                     objActivity = new ReportGenerator(); 
                     */
                     objActivity = FactoryPattern<IActivity, ReportGenerator>.CreateInstance();
                     break;
              case Enumeration.ModuleName.ReportAnalyser:
                     /* Old coding ...
                     objActivity = new ReportAnalyser();
                     */
                     objActivity = FactoryPattern<IActivity, ReportAnalyser>.CreateInstance();
                     break;
              default:
                     break;
         }
         return objActivity;
      }
    }