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Inverting Inversion of Control

What do you think about this code?

IoC.Container.Kernel.AddComponentInstance<IFoo>(this);
IBar context = IoC.Resolve<IBar>();//needs IFoo

For some reason it looks really funny to me.

More seriously, this is a good way to involve components that you cannot control in the container.

Print | posted on Monday, December 10, 2007 1:36 AM

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# re: Inverting Inversion of Control 12/10/2007 2:45 AM Barry Dahlberg

By "components that you cannot control" do you mean those provided by a third party for example? It seems like if you can reference it by "this" you probably have control over it... unless you are inheriting from something?

I ask because I had similar code at one point but factored it out as it seemed like I had the owner of the container at the wrong level.

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# re: Inverting Inversion of Control 12/10/2007 2:57 AM Ayende Rahien

By components that you don't control I mean stuff that is instantiated for you. Consider something like a COM component that is being instantiated for you by the runtime. You can probably work around that, but it is a real PITA to do, so this is a good way to handle that.

There are many cases where this is true, usually when you are writing plugins to things

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# re: Inverting Inversion of Control 12/10/2007 6:29 PM Ivan Krivyakov

This code makes a lot of sense to me.
E.g. imagine your application has command line arguments that influence what objects are created and with what parameters. This would be a perfect way to inject command line info into your IoC containter.

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# re: Inverting Inversion of Control 12/10/2007 8:03 PM Ron Grabowski

I asked question about this on the Castle forums in 2006:

http://forum.castleproject.org/viewtopic.php?t=1614

In that example I wanted to give the container an existing IPersonService instance and have the container set its Logger property with a Logger from the container.

Another use might be for dipping (think dipping an a cookie in a glass of milk: temporarly placing the instance in the container so its dependencies get satisfied then removing it) the returned handler from PageParser.GetCompiledPageInstance into the container so it can have additional properties filled before processing:

IHttpHandler handler =
PageParser.GetCompiledPageInstance(aspxPagePath, null, context);

// set the Logger property on the handler instance
if (handler is IRequiresLogger)
{
container.Inject<IRequiresLogger>(handler);
}

handler.ProcessRequest(context);

or in more general terms:

container.Inject(handler);

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