I'm a long-time Windows developer, having cut my teeth on win32 and early COM. I've been working with .NET since 2001, so I'm pretty fluent in C# and the CLR. I'd never heard of Castle Windsor until I started participating in Stack Overflow. I've read the Castle Windsor "Getting Started" guide, but it's not clicking.
Teach this old dog new tricks, and tell me why I should be integrating Castle Windsor into my enterprise apps.
Castle Windsor is an inversion of control tool. There are others like it.
It can give you objects with pre-built and pre-wired dependencies right in there. An entire object graph created via reflection and configuration rather than the "new" operator.
Start here: http://tech.groups.yahoo.com/group/altdotnet/message/10434
Imagine you have an email sending class. EmailSender. Imagine you have another class WorkflowStepper. Inside WorkflowStepper you need to use EmailSender.
You could always say new EmailSender().Send(emailMessage);
but that - the use of new - creates a TIGHT COUPLING that is hard to change. (this is a tiny contrived example after all)
So what if, instead of newing this bad boy up inside WorkflowStepper, you just passed it into the constructor?
So then whoever called it had to new up the EmailSender.
new WorkflowStepper(emailSender).Step()
Imagine you have hundreds of these little classes that only have one responsibility (google SRP).. and you use a few of them in WorkflowStepper:
new WorkflowStepper(emailSender, alertRegistry, databaseConnection).Step()
Imagine not worrying about the details of EmailSender when you are writing WorkflowStepper or AlertRegistry
You just worry about the concern you are working with.
Imagine this whole graph (tree) of objects and dependencies gets wired up at RUN TIME, so that when you do this:
WorkflowStepper stepper = Container.Get<WorkflowStepper>();
you get a real deal WorkflowStepper with all the dependencies automatically filled in where you need them.
newIt just happens - because it knows what needs what.
And you can write fewer defects with better designed, DRY code in a testable and repeatable way.
Put simply. Imagine you have some class buried in your code that needs a few simple config values to do its job. That means everything that creates an instance of that class needs to get those dependencies, so you usually end up having to refactor loads of classes along the way to just pass a bit of config down to where the instance gets created.
So either lots of classes are needlessly altered, you bunch the config values into one big config class which is also bad... or worst still go Service Locator!
IoC allows your class to get all its depencencies without that hassle, and manages lifetimes of instances more explicitly too.