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Define your own IoC container

, 23 Mar 2012
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How to define a simple IoC Container.

This is a simple IoC Container.

Last year I was assigned to develop an IoC container for R&D purposes which made me start working with IoC Containers. I share with you here part of it as I think it might help you a lot when you develop your own container.

The Inversion of Control (IoC) and Dependency Injection (DI) patterns are all about eliminating dependencies from your code. Dependency Injection is well-known as “Inversion of Control” whose principle is – “Don’t call us, we’ll call you”. So we can say that IoC is the principle whereas DI is the way of implementation. There are three popular ways of Inversion of Control namely:

  1. Constructor Injection
  2. Method Injection
  3. Property Injection

I am not going to discuss about IoC or DI rather I want to show how to implement your own IoC Container. However if you want to know the details about IoC and DI, please have a look at this link.

Let's move to our code portion: 

public static class IoC
{
    private static readonly IDictionary<Type, Type> types = new Dictionary<Type, Type>();
    private static readonly IDictionary<Type, object> typeInstances = new Dictionary<Type, object>();
    public static void Register<TContract, TImplementation>()
    {
        types[typeof(TContract)] = typeof(TImplementation);
    }
    public static void Register<TContract, TImplementation>(TImplementation instance)
    {
        typeInstances[typeof(TContract)] = instance;
    }
    public static T Resolve<T>()
    {
        return (T)Resolve(typeof(T));
    }
    public static object Resolve(Type contract)
    {
        if (typeInstances.ContainsKey(contract))
        {
            return typeInstances[contract];
        }
        else
        {
            Type implementation = types[contract];
            ConstructorInfo constructor = implementation.GetConstructors()[0];
            ParameterInfo[] constructorParameters = constructor.GetParameters();
            if (constructorParameters.Length == 0)
            {
                return Activator.CreateInstance(implementation);
            }
            List<object> parameters = new List<object>(constructorParameters.Length);
            foreach (ParameterInfo parameterInfo in constructorParameters)
            {
                parameters.Add(Resolve(parameterInfo.ParameterType));
            }
            return constructor.Invoke(parameters.ToArray());
        }
    }
}

Now from your bootstrapper class, you need to register your class like:

Service svc= new Service ();
IoC.Register<IService , Service >(svc);

On subsequent classes, you just need to inject the Interface or class that you register like:

private IService currentSvc = null;
public LoginServices(IService  submittedService)
{
    this.currentSvc =submittedService;
}

Very very simple!!!! We love simple, don’t we?

Updated: 19 March2012

Example: Say this is my Interface,

public interface ILogger
{
    void Log(string submittedMsg);
}

The Logger class implements this interface.

public class Logger :ILogger
{
    public void Log(string submittedMsg)
    {
        if (!string.IsNullOrEmpty(submittedMsg))
        {
            Console.WriteLine(string.Format("[{0}] {1}\r\n", DateTime.Now, submittedMsg));
            Console.Read();
        }
    }
}

In this ConsoleLogger class, I inject the ILogger to its constructor,

public class ConsoleLogger
{
   private ILogger logger = null;

   public ConsoleLogger(ILogger submittedLogger)
   {
       this.logger = submittedLogger;
       this.DisplayMessage();
   }

   public void DisplayMessage()
   {
       logger.Log("Hi..See it is working!!");
   }
}

Register and Resolve options:

class Program
{
    static void Main(string[] args)
    {
        IoC.Register<ILogger, Logger>();

        IoC.Register<ConsoleLogger, ConsoleLogger>();
        ConsoleLogger objCOnsoleLogger=IoC.Resolve<ConsoleLogger>();       
    }
}

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Md. Rashim uddin
Software Developer (Senior) KAZ Software Limited.
Bangladesh Bangladesh
I am a true visionary as well as have always been passionate about learning. I always love to work with thought-provoking personnel to develop amazing, exciting and innovative ideas as part of an aggressive team that challenges my ingenious ideas, creativeness and extensive experience.
 
My Blog: http://rashimuddin.wordpress.com/
 
My Email: rashimiiuc at yahoo dot com
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Comments and Discussions

 
SuggestionAn improvement Pinmemberdcjpriv26-Mar-12 14:04 
GeneralMy vote of 5 Pinmemberenamur18-Mar-12 19:59 
GeneralRe: My vote of 5 PinmemberMd. Rashim uddin18-Mar-12 20:10 
GeneralRe: My vote of 5 PinmemberMd. Rashim uddin18-Mar-12 20:12 
GeneralRe: My vote of 5 Pinmemberenamur18-Mar-12 21:20 
GeneralRe: My vote of 5 PinmemberMd. Rashim uddin18-Mar-12 21:30 
GeneralMy vote of 5 PinmemberSaiyed Alam18-Mar-12 9:31 
GeneralRe: My vote of 5 PinmemberMd. Rashim uddin18-Mar-12 20:10 
Thanks
QuestionExample Please PinmemberKevin Marois15-Mar-12 6:12 
AnswerRe: Example Please PinmemberMd. Rashim uddin15-Mar-12 8:21 
General5 - Re: Example Please PinmemberKevin Marois15-Mar-12 8:28 
GeneralRe: 5 - Re: Example Please PinmemberMd. Rashim uddin15-Mar-12 8:32 

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