Thursday, January 07, 2010

Twelve Days of Code – Unity Framework

As part of the twelve days of code, I’m building a Pomodoro style task tracking application and blogging about it. This post is the seventh in this series. This post focuses on using the Microsoft Unity Framework in our .NET 4.0 application.

This post assumes assumes that you are familiar with the last few posts and have a working understanding of Inversion of Control.  If you’re new to this series, please check out some of the previous posts and then come back.  If you’ve never worked with Inversion of Control, it’s primarily about decoupling objects from their implementation (Factory Pattern, Dependency Injection, Service Locator) – but the best place to start is probably here.


Our goal for this post is to remove as many hard-code references to types as possible.  Currently, the constructor of our MainWindow initializes all the dependencies of the Model and then manually sets the DataContext.  We need to pull this out of the constructor and decouple the binding from TaskApplicationViewModel to ITaskApplication.

Initializing the Container

We’ll introduce our inversion of control container in the Application’s OnStartup event.  The container’s job is to provide type location and object lifetime management for our objects, so all the hard-coded initialization logic in the MainWindow constructor is registered here.

public partial class App : Application
    protected override void OnStartup(StartupEventArgs e)
        IUnityContainer container = new UnityContainer();
        container.RegisterType<ITaskApplication, TaskApplicationViewModel>();
        container.RegisterType<ITaskSessionController, TaskSessionController>();
        container.RegisterType<IAlarmController, TaskAlarmController>();
        container.RegisterType<ISessionRepository, TaskSessionRepository>();

        Window window = new MainWindow();
        window.DataContext = container.Resolve<ITaskApplication>();


Also note, we’re initializing the MainWindow with our data context and then displaying the window.  This small change means that we must remove the MainWindow.xaml reference in the App.xaml (otherwise we’ll launch two windows).

Next Steps

Aside from the simplified object construction, it would appear that the above code doesn’t buy us much: we have roughly the same number of lines of code and we are simply delegating objection construction to Unity.  Alternatively, we could move the hard-coded registrations to a configuration file (though that’s not my preference here).

In the next post, we’ll see how using Prism’s Bootstrapper and Module configuration allows us to move this logic into their own modules.

In the next step, we’ll look at using P

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