.NET Junkie

Download: The Simple Service Locator library and source code can be downloaded from CodePlex.com. Visit the homepage at simpleservicelocator.codeplex.com or go directly to the Downloads tab.

Many development teams I help have legacy code bases with little or no unit tests. As you can imagine, the complexity makes it hard to add new features and fix existing bugs. Changing the course is often not easy, because the developers need to learn a whole new back of tricks. One of those tricks is unit testing and to me inextricably connected with that is dependency injection.

To get teams on the road quickly I often want to do the simplest thing that could possibly work. For that reason I've been annoyed with the complexity of the popular inversion of control frameworks. The concepts of inversion of control (IoC), dependency injection and good RTM unit tests are by itself hard enough to gasp for many developers. Learning to work with and configure several different frameworks (such as logging, validation, O/RM, and dependency injection) at the same time makes it even harder.

For this reason I started the Simple Service Locator project on CodePlex. It’s a (yet another) IoC library for .NET. Key features are its simplicity and it being an implementation of the Common Service Locator interface. This makes it especially useful for development teams unfamiliar with one of the existing IoC frameworks. Development teams can start using the Simple Service Locator and replace it with a more feature-rich IoC framework later on when needed, without having to alter any production code. For the lifetime of many projects however, I expect the Simple Service Locator just to be sufficient.

Simple Service Locator is an implementation of the Common Service Locator (CSL) interface and is not meant to be used without it. Therefore production code should only call CSL's ServiceLocator facade, as is shown in the following example:

IWeapon weapon = ServiceLocator.Current.GetInstance<IWeapon>();

Configuring the Simple Service Locator is done in the startup path of the application, as can be seen below. In this example you see how the Simple Service Locator is configured in the Application_Start event of the global.asax of a ASP.NET web application.

using System;
using CuttingEdge.ServiceLocation;
using Microsoft.Practices.ServiceLocation;

public class Global : System.Web.HttpApplication
{
    protected void Application_Start(object sender, EventArgs e)
    {
        // 1. Create a new Simple Service Locator container
        var container = new SimpleServiceLocator();

        // 2. Configure the container

        // Register a delegate that will create a new
        // instance on each call to GetInstance<Warrior>.
        container.Register<Warrior>(() =>
            {
                var weapon = container.GetInstance<IWeapon>();
                return new Samurai(weapon);
            });

        // Register a single object instance that always
        // be returned (must be thread-safe).
        container.RegisterSingle<IWeapon>(new Katana());

        // 3. Register the container to the Common Locator
        ServiceLocator.SetLocatorProvider(() => container);
    }
}

Please visit the Simple Service Locator home page to see more code examples.

The project is currently in beta, which means your feedback is very welcome. What do you think of the current API? Can we make it even simpler? Do you miss anything? I like to know.

Cheers.

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