CODEWITHSUNDEEP
c#
Newbie
Newbie

Reputation: 1111

Cannot understand the behaviour of C# compiler while instantiating a class thru interface

I have a class that implements an interface. The interface is 

public interface IRiskFactory
{
   void StartService();
   void StopService();
}

The class that implements the interface is 

public class RiskFactoryService : IRiskFactory
{
}

Now I have a console application and one window service.

From the console application if I write the following code

static void Main(string[] args)
{
    IRiskFactory objIRiskFactory = new RiskFactoryService();
    objIRiskFactory.StartService();
    Console.ReadLine();
    objIRiskFactory.StopService();
}

It is working fine. However, when I mwrite the same piece of code in Window service

public partial class RiskFactoryService : ServiceBase
{
    IRiskFactory objIRiskFactory = null;
    public RiskFactoryService()
    {
        InitializeComponent();
        objIRiskFactory = new RiskFactoryService(); <- ERROR
    }

    /// <summary>
    /// Starts the service
    /// </summary>
    /// <param name="args"></param>
    protected override void OnStart(string[] args)
    {
        objIRiskFactory.StartService();
    }

    /// <summary>
    /// Stops the service
    /// </summary>
    protected override void OnStop()
    {
        objIRiskFactory.StopService();
    }
}

It throws error: Cannot implicitly convert type 'RiskFactoryService' to 'IRiskFactory'. An explicit conversion exists (are you missing a cast?)

When I type cast to the interface type, it started working

objIRiskFactory = (IRiskFactory)new RiskFactoryService();

My question is why so?

Upvotes: 1

Views: 152

Answers (3)

Marc Gravell
Marc Gravell

Reputation: 1064204

Two thoughts occur:

  • if you are using partial to have the service / interface parts of the type in separate files (since the code mentions partial and doesn't seem to implement the interface itself) are the namespaces correct? With partial classes it is perilously easy to accidentally end up creating two types rather than one type
  • is IRiskFactory suffering from resolution issues (perhaps from having a referenced dll and a local copy)? i.e. is all the code talking about the same IRiskFactory ?

Upvotes: 2

Akash Kava
Akash Kava

Reputation: 39956

Shouldnt your windows service class actually implement service like below ...

public partial class RiskFactoryService : ServiceBase  , IRiskFactory
{
}

and why are you creating RiskFactoryService in constructor of RiskFactoryService, i think this will give stack overflow error !! You can simply call , this.StartService()...

Upvotes: 2

ExplodingRabbit
ExplodingRabbit

Reputation: 29

I think the problem is that in this case RiskFactoryService is referring to the partial class definition RiskFactoryService : ServiceBase which does not implement IRiskFactory (did you mean that class to be the same as the RiskFactoryService class that does implement IRiskFactory? - if so that class definition should probably be marked partial as well).

A more pressing problem I see is that you are recursively calling the constructor for the RiskFactoryService class inside itself. This means that every time you try to instantiate a RiskFactoryService the stack will overflow.

Upvotes: 0

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