How To Use Unity Container In ASP.NET

Today’s post will explain how to include Unity container
in ASP.NET web applications. The details I write here are based on David Hayden’s screen cast and therefore the credit is for David Hayden. Another good example of how to use Unity container through WCF service can be found in this post.
Building The Container The first thing to do is to build the Unity container. We would like to have a persistent container that hold it’s state during the running of the application. The right place to put the is as part of the Global.asax file as a property of the current running application. First build an interface for the container property:
public interface IContainerAccessor
{
IUnityContainer Container { get; }
}
After the building of the interface implement it in the Global class in the Global.asax file:
public class Global : HttpApplication, IContainerAccessor
{
#region Members

private static IUnityContainer _container;

#endregion

#region Properties

///

/// The Unity container for the current application
///

public static IUnityContainer Container
{
get
{
return _container;
}
set
{
_container = value;
}
}

#endregion

#region IContainerAccessor Members

///

/// Returns the Unity container of the application
///

IUnityContainer IContainerAccessor.Container
{
get
{
return Container;
}
}

#endregion

#region Application Events

protected void Application_Start(object sender, EventArgs e)
{
BuildContainer();
}

protected void Application_End(object sender, EventArgs e)
{
CleanUp();
}

#endregion

#region Methods

private static void BuildContainer()
{
IUnityContainer container = new UnityContainer();

// Register the relevant types for the
// container here through classes or configuration

// register the container in the container property
Container = container;
}

private static void CleanUp()
{
if (Container != null)
{
Container.Dispose();
}
}

#endregion
}
In the implementation you hold a static container variable which will be available in the web application through the interface we build. In the BuildContainer method we do all the work of registering types and instances to the Unity container. It can be done by code or by configuration this decision is yours.
How To Inject Dependencies After you set up your container it’s time to use it. It is done by building a base page for all the pages in your application. The injection of dependencies should be done very early in the page life cycle and therefore implemented in the OnPreInit event. The base page class can look like:
public abstract class BasePage : Page where T : class
{
protected override void OnPreInit(EventArgs e)
{
InjectDependencies();
base.OnPreInit(e);
}

protected virtual void InjectDependencies()
{
var context = HttpContext.Current;

if (context == null)
{
return;
}

var accessor = context.ApplicationInstance as IContainerAccessor;

if (accessor == null)
{
return;
}

var container = accessor.Container;

if (container == null)
{
throw new InvalidOperationException("No Unity container found");
}

container.BuildUp(this as T);
}
}
All the checks in the InjectDependencies method are a guarantee that we have a Unity container. The only interesting part here is the BuildUp method in the end of the method. The BuildUp method will ensure that the injection will happen as required. Example Of Concrete Page After building the base page the only thing to do next is to implement the other pages and inheriting from the base page. The next example shows how to use the previous BasePage class:
public partial class _Default : BasePage<_default>
{
#region Properties

[Dependency]
private ILogger Logger { set; get; }

#endregion

#region Page Events

protected void Page_Load(object sender, EventArgs e)
{
Logger.Log("Something");
}

#endregion
}
Summary To sum up the post, I showed an example that was suggested by David Hayden of how to use Unity in ASP.NET application. This is a very simple example that will help you to get started with Unity in your web applications. I suggest to see David Hayden’s screen cast for more details.