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.NET Forum / Languages / C# / February 2008Understanding IoC and Dependency Injection.
I am trying to understand IoC and Dependency Injection. Some places claim they are the same thing, others claim that they are different. I've looked at code samples for both. It seems like the technique is not much more than loading an object, defined by an interface, on the fly from an outside assembly based on the value in a configuration file (or some other place). Is that all or am I missing something? Is this pretty much the same as COM technique 10 years ago that was known as loading a Late Bound object against an interface? Thanks. Assuming this isn't a troll (sorry, but your post-count makes me very suspicious), then that sounds about right... call it what you like: factory, plugin, ioc, dependency injection, interface-first - all the same fundamental idea. > as loading a Late Bound object against an interface? It surely can't be both late bound and using the interface at the same time? Marc > Assuming this isn't a troll (sorry, but your post-count makes me very > suspicious), That was unfair and completely uncalled for. I have often wondered the same thing and from the way post was worded I am pretty sure the question was genuine. Why not just answer the question, see how the thread develops and then decide whether you want to contribute further or not? > That was unfair and completely uncalled for. OK; I'll take that on the chin... you are correct and I apologise: Frank - I'm sorry. If I can briefly explain - the question seemed remarkably like one very recently, so I checked history to see if it was the same poster, and immediately google-groups showed me 40k-odd posts, not all of an appreciable nature... unfortunately google-groops *doesn't* show the e- mail address by default (you have to go through a captcha) - otherwise I would have noticed the open e-mail address "none@none.net", so I was incorrect to attribute the other threads to Frank. So yes: I got it wrong; but I did also at least offer some input to the question. Marc >> That was unfair and completely uncalled for. > OK; I'll take that on the chin... you are correct and I apologise: [quoted text clipped - 7 lines] > I would have noticed the open e-mail address "none@none.net", so I was > incorrect to attribute the other threads to Frank. That's fine. Apology accepted. Frank Rizzo, is, of course, not my real name. But I am not a troll, by my count (thunderbird makes it really convinient), I have 59 posts in this forum under this nom de guerre. The reason for none@none.net is spam. > So yes: I got it wrong; but I did also at least offer some input to > the question. > > Marc > The reason for n...@none.net is spam. Tell me about it... you don't want to /know/ how much spam my gmail address gets, thanks mainly to using it for nntp... but it makes it easier to dig out old posts when the common "how to..." questions come up ;-p Marc > Assuming this isn't a troll (sorry, but your post-count makes me very > suspicious), then that sounds about right... call it what you like: [quoted text clipped - 4 lines] > It surely can't be both late bound and using the interface at the same > time? Huh? In VB6, that was the only way to implement IoC. dim oMySqlDataLoader as IDataLoader dim oMsSqlDataLoader as IDataLoader set oMySqlDataLoader = CreateObject("DataLoader.MySqlVariety") set oMsSqlDataLoader = CreateObject("DataLoader.MicrosoftVariety") > Huh? In VB6, that was the only way to implement IoC. > [quoted text clipped - 3 lines] > set oMySqlDataLoader = CreateObject("DataLoader.MySqlVariety") > set oMsSqlDataLoader = CreateObject("DataLoader.MicrosoftVariety") I think this is a trivial terminology thing... It has been a few years since I really did COM, but IIR that isn't strictly late-bound; late-bound denotes using IDispatch; however, interface-binding denotes vtable-binding (unless the automation server only supports IDispatch, which would be uncommon). I suspect that in the above code, the "Set ... = " is actually using IUnkown.QueryInterface to bind to the vtable of IDataLoader, and is not late-bound. To do this using late binding you would dim "As Object". Marc > > Assuming this isn't a troll (sorry, but your post-count makes me very > > suspicious), then that sounds about right... call it what you like: [quoted text clipped - 12 lines] > set oMySqlDataLoader = CreateObject("DataLoader.MySqlVariety") > set oMsSqlDataLoader = CreateObject("DataLoader.MicrosoftVariety") That's not IoC though. The point of IoC is that the objects are *told* about their dependencies rather than creating the objects themselves. So in unit tests you tell your objects to use some mock interface implementations, and in the real code you tell your objects (usually with a configuration file) to use some specific real implementation.  SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk > That's not IoC though. To be fair - it is a little hard to tell from just this (abbreviated) context... replace "DataLoader.MySqlVariety" with sProcSig[*] and you're pretty-much there for IoC with a factory-oriented implementation... Marc [*]=well, it wouldn't be VB without a little Hungarian ;-p > I am trying to understand IoC and Dependency Injection. Some places > claim they are the same thing, others claim that they are different. > I've looked at code samples for both. I think http://en.wikipedia.org/wiki/Dependency_injection is rather accurate: #Dependency injection (DI) refers to the process of supplying an #external dependency to a software component and is a specific form of #inversion of control where the concern being inverted is the process of #obtaining the needed dependency. > It seems like the technique is not much more than loading an object, > defined by an interface, on the fly from an outside assembly based on [quoted text clipped - 3 lines] > Is this pretty much the same as COM technique 10 years ago that was > known as loading a Late Bound object against an interface? The concept as such is not new. The way it is used in something like http://www.springframework.net/ has evolved. Arne >> I am trying to understand IoC and Dependency Injection. Some places >> claim they are the same thing, others claim that they are different. [quoted text clipped - 22 lines] > > Arne Thanks for the explanation. I always get initially confused when a well known design, that was used in the past, all of a sudden becomes in vogue and gets a new name. Like "refactoring" used to be known as "reshuffling your code to make it easier to understand". Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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