At work I have used a variety of IOC Containers including
- MEF : http://mef.codeplex.com/ which is now freely available as part of .NET in the System.Composition namespace
- Castle : http://www.castleproject.org/
And I have used others such as Unity/StructureMap/AutoFac. They are all very good and very rich.
For those of you who don’t know what IOC stands for, it stands for Inversion Of Control. Which is described as follows:
In software engineering, inversion of control (IoC) is a programming technique, expressed here in terms of object-oriented programming, in which object coupling is bound at run time by an assembler object and is typically not known at compile time using static analysis.
In traditional programming, the flow of the business logic is determined by objects that are statically assigned to one another. With inversion of control, the flow depends on the object graph that is instantiated by the assembler and is made possible by object interactions being defined through abstractions. The binding process is achieved through dependency injection, although some argue that the use of a service locator also provides inversion of control.
In order for the assembler to bind objects to one another, the objects must possess compatible abstractions. For example, class A may delegate behavior to interface I which is implemented by class B; the assembler instantiates A and B then injects B to A.
In practice, inversion of control is a style of software construction where reusable code controls the execution of problem-specific code. It carries the strong connotation that the reusable code and the problem-specific code are developed independently, which often results in a single integrated application. Inversion of control as a design guideline serves the following purposes:
- There is a decoupling of the execution of a certain task from implementation.
- Every module can focus on what it is designed for.
- Modules make no assumptions about what other systems do but rely on their contracts.
- Replacing modules has no side effect on other modules.
- Inversion of control is sometimes facetiously referred to as the "Hollywood Principle: Don’t call us, we’ll call you", because program logic runs against abstractions such as callbacks.
Wikipedia : up on date 25/02/2013
Thing is I have always wanted to try and make one of these myself, just to see what is involved. I did not want to go too nuts on this, and just wanted the following really:
- Instance configuration : singleton / transient
- Simple registration process, maybe some sort of fluent interface
- Use the Expression API to compile into delegates for quick creation of objects
- Constructor / property injection
- Provide the ability to accept non IOC held constructor parameters
So those couple of points are ALL I wanted to get working. As I say there are a whole slew of full fledged IOC containers out there (where I have named a few above), this articles container is more of a learning exercise, that I thought I would share, in case anyone else is interested in this sort of thing.
I am calling my container
BarbarianIOC as the existing containers all seems to have these short snappy names, and it’s kind of play on my name, and if you saw me without a shave I do kinda look a bit like a barbarian.
If you want to read more you can grab the rest of the article and the source over at codeproject : http://www.codeproject.com/Articles/552514/BarbarianIOC-A-simple-IOC-Container