Multiple Dependency Injection using Ninject

Question

I am trying to do multiple dependency injection using Ninject. I have 3 classes, EmailHelper, ExceptionHelper and ReportHelper. ExceptionHelper class requires EmailHelper and ReportHelper requires ExceptionHelper. Here is my code.

IKernel _kernel = new StandardKernel();
_kernel.Load(Assembly.GetExecutingAssembly());

IEmailHelper _emailHelper = _kernel.Get<IEmailHelper>(); 

ExceptionHelper exceptionHelper = new ExceptionHelper(_emailHelper);
ReportHelper reportHelper       = new ReportHelper(exceptionHelper);

ExceptionHelper and IEmailHelper seems loosely coupled, but ReportHelper and ExceptionHelper are still tightly coupled.

How can I make ReportHelper and ExceptionHelper loosely coupled?

Can I modify my code like this ?

IExceptionHelper _exceptionHelper = _kernel.Get<IExceptionHelper>();
ReportHelper reportHelper = new ReportHelper(_exceptionHelper);

But IExceptionHelper is not initiated with IEmailHelper? I am confused.

[edited]

Here is my ExceptionHelper constructor. Rest constructor has same structure.

private IEmailHelper _emailHelper;
public ExceptionHelper(IEmailHelper eh)
{
    _emailHelper = eh;
}

Can you include the constructors of those classes in your question? — Yacoub Massad
– Yacoub Massad, Commented Nov 2, 2015 at 15:20

Yacoub Massad · Accepted Answer · 2015-11-02 15:36:23Z

2

The constructors of your classes should look like something like this:

public ExceptionHelper(IEmailHelper email_helper)
{
    m_EmailHelper = email_helper;
}

public ReportHelper(IExceptionHelper exception_helper)
{
    m_ExceptionHelper = exception_helper;
}

Then you need to make sure that all of your types are registered with the container like this (or use other automatic ways of registration):

kernel.Bind<IReportHelper>().To<ReportHelper>();
kernel.Bind<IExceptionHelper>().To<ExceptionHelper>();
kernel.Bind<IEmailHelper>().To<EmailHelper>();

Then you can build a IReportHelper instance like this:

IReportHelper report_helper = kernel.Get<IReportHelper>();

And the container will manage the wiring automatically.

answered Nov 2, 2015 at 15:36

Yacoub Massad

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2 Comments

jkl Over a year ago

I don't understand IReportHelper report_helper = kernel.Get<IReportHelper>() this part. I don't need to pass IExceptionHelper instance as parameter?

Yacoub Massad Over a year ago

Yes. The DI container will detect that the constructor of ReportHelper requires a IExceptionHelper dependency and it will be able to inject it. This is called Auto Wiring.

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