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An especially attractive .NET dependency injection library
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SexyInject is a dependency injection framework. It is designed to be flexible such that you can create very general bindings that satisfy a rich set of types. For example, many DI frameworks have built-in support for injecting Func<T> into your types such that it ends up being a factory function for T. While SexyInject also supports this natively, it is implemented as a simple extension method that you could have written yourself, which demonstrates that if the facility weren't already included, it would have been trivial for you to add that functionality yourself. Later on, we'll take a look at that extension method and break it down piece by piece.


Use NuGet, of course!

Instal-Package SexyInject

Quick Start

Generally speaking, the two main use-cases for a DI framework are to provide instances of classes on request, and to provide implementations of interfaces in like fashion. SexyInject works both as a service locator (I want an instance of something, give it to me!) and as a dependency injector (My class has lots of dependencies: fulfill them for me!).

Those two scenarios are not strictly mutually exclusive, since even with dependency injection, you need a bootstrap scenario that will give you an instance of a class with its dependencies resolved. For example, in ASP.NET MVC, you're going to need an instance of a controller instantiated with its dependencies resolved. That can't happen in pure DI -- you're going to need to "ask" for that instance from the "service locator" when trying to instantiate the controller. From that point on, however, DI should take over and generally speaking you shouldn't have to talk to the service locator ever again.

So with that boilerplate out of the way, how do you use this framework? The central class is named Registry. It's the "container", so to speak. It is on this class that you register bindings which dictate precisely how a request for some type is resolved. It is also the class with which you interact in order to obtain an instance of such a type. (service-locator style; that will actually be the main style on which we focus, since DI is implicit in those scenarios)

So. Let's start from scratch. Let's create a registry and try to obtain an instance of a type from it:

var registry = new Registry();
var instance = registry.Get<Foo>();

That's the basic scenario. There's just one fly in the ointment. If you actually try this code it won't work. You'll get an exception complaining that the type Foo has not been registered. So let's make clear one important point from the start: with SexyInject no type will be available by default. You can't even request an instance of some ordinary type with a default constructor without getting rejected. But that's an important part of the design -- we want all the behavior provided by the framework to be purely opt-in. Fortunately, opting-in to such scenarios is easy!

Typical Setup

So now that we've gotten out of the way the notion that you're going to have to configure a few things before you can even properly use the framework, let's demonstrate what a normal minimalist scenario might look like.

var registry = new Registry();

That second line is what allows the framework to resolve types that are obviously straightforward to realize. Things like classes with defualt constructors, or classes that have constructors with parameters that are similarly straightforward to resolve. So with that, now we can have the line:

var instance = registry.Get<Foo>();

Assuming Foo has a constructor that is either parameterless, or only has dependencies that are equally easy to resolve, that's all you have to do in terms of setup.

That being said, that is ignoring probably the most ubiquitous use-case for DI, resolving an interface into a particular implementation of that interface. So let's tackle that now:

registry.Bind<IFoo>(x => x.To<Foo>());

Here we say that for any request for an instance of the interface IFoo, provide an instance of the class Foo (which must implement that interface -- the generic type constraints will enforce this).

Full Documentation

To read the documentation in full, visit the project's GitBook site.

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