Unity and ASP.NET

Using Dependency Injection in a website can get a little dodgy, but in my ASP.NET site use the same base code as my WPF app, I needed a little dependency injection to resolve references at runtime when the application type is known. Now in your ASP.NET page just like in your WPF application you need a little extra bit to get it all going. Finding this for WPF is easy, not so much in ASP.

 1Imports System.Web
 2Imports System.Web.UI
 3Imports Microsoft.Practices.Unity
 4''' <summary>
 5''' C# version and source
 6''' http://blogs.msdn.com/mpuleio/archive/2008/07/17/proof-of-concept-a-simple-di-solution-for-asp-net-webforms.aspx
 7''' </summary>
 8''' <remarks></remarks>
 9Public Class UnityHttpModule
10    Implements IHttpModule
11
12    Public Sub Dispose() Implements System.Web.IHttpModule.Dispose
13
14    End Sub
15
16    Public Sub Init(ByVal context As System.Web.HttpApplication) Implements System.Web.IHttpModule.Init
17        AddHandler context.PreRequestHandlerExecute, AddressOf OnPreRequestHandlerExecute
18    End Sub
19
20    Private Sub OnPreRequestHandlerExecute(ByVal sender As Object, ByVal e As EventArgs)
21        Dim handler As IHttpHandler = HttpContext.Current.Handler
22        If TypeOf handler Is Page Then
23            My.Unity.Container.BuildUp(handler.GetType(), handler)
24
25            ' User Controls are ready to be built up after the page initialization is complete
26            Dim page As Page = handler
27            If Not page Is Nothing Then
28                AddHandler page.InitComplete, AddressOf OnPageInitComplete
29            End If
30        End If
31    End Sub
32
33    Private Sub OnPageInitComplete(ByVal sender As Object, ByVal e As EventArgs)
34        Dim page As Web.UI.Page = sender
35        For Each c In BuildControlTree(page)
36            Try
37                My.Unity.Container.BuildUp(c.GetType(), c)
38            Catch ex As Exception
39                ' TODO: Some sort of error handling if important
40                WebPortalTrace.Verbose(WebPortalTraceType.Unity, "Unity unable to build up {0}", c.GetType)
41            End Try
42        Next
43    End Sub
44
45    ' Get the controls in the page's control tree excluding the page itself
46    Private Function BuildControlTree(ByVal root As Control) As List(Of Control)
47        Dim ct As New List(Of Control)
48        For Each c In root.Controls
49            ct.Add(c)
50            ct.AddRange(BuildControlTree(c))
51        Next
52        Return ct
53    End Function
54
55End Class

All you need is to put a reference into your config file:

1  <system.web>
2    <httpModules>
3      <add name="UnityHttpModule" type="Company.Product.UnityHttpModule, Company.Product"/>
4    </httpModules>
5  </system.web>

And off you go, before you know it you will have dependency injection coming out of your ears.

One of the advantages to using dependency injection is that you could change a piece of functionality without having to recompile and redeploy your site! How about this…

1<unity>
2    <containers>
3      <container>
4        <types>
5          <type type="Company.Product.ViewModels.IRecentItemsViewModel, Company.Product" mapTo="Company.Product.ViewModels.RecentItemsViewModel, Company.Product" />
6        </types>
7      </container>
8    </containers>
9</unity>

The business then decide that they have to have the order of the recent items list changed but that it needs to go into production immediately, so your testing cycle is extremely tight. No problem… fire up a new solution and create a new class that inherits from IRecentItemsViewModel and implement the new functionality. Then compile it as “Company.Product.Hotfix1”, drop it into your test site bin folder and change line above to:

1<unity>
2    <containers>
3      <container>
4        <types>
5          <type type="Company.Product.ViewModels.IRecentItemsViewModel, Company.Product" mapTo="Company.Product.Hotfix1.ViewModels.RecentItemsViewModel, Company.Product.Hotfix1" />
6        </types>
7      </container>
8    </containers>
9</unity>

The site will then load your new code and you can test the only functionality that you have changed, before deploying to production. Now this may not seam like much, but if your system is made up of thousands of views then you may just need this functionality. And it is so easy to achieve that even for small projects it is fantastic.

P.S. Works with MVC… shhhh…

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