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.
Imports System.Web Imports System.Web.UI Imports Microsoft.Practices.Unity ''' <summary> ''' C# version and source ''' http://blogs.msdn.com/mpuleio/archive/2008/07/17/proof-of-concept-a-simple-di-solution-for-asp-net-webforms.aspx ''' </summary> ''' <remarks></remarks> Public Class UnityHttpModule Implements IHttpModule Public Sub Dispose() Implements System.Web.IHttpModule.Dispose End Sub Public Sub Init(ByVal context As System.Web.HttpApplication) Implements System.Web.IHttpModule.Init AddHandler context.PreRequestHandlerExecute, AddressOf OnPreRequestHandlerExecute End Sub Private Sub OnPreRequestHandlerExecute(ByVal sender As Object, ByVal e As EventArgs) Dim handler As IHttpHandler = HttpContext.Current.Handler If TypeOf handler Is Page Then My.Unity.Container.BuildUp(handler.GetType(), handler) ' User Controls are ready to be built up after the page initialization is complete Dim page As Page = handler If Not page Is Nothing Then AddHandler page.InitComplete, AddressOf OnPageInitComplete End If End If End Sub Private Sub OnPageInitComplete(ByVal sender As Object, ByVal e As EventArgs) Dim page As Web.UI.Page = sender For Each c In BuildControlTree(page) Try My.Unity.Container.BuildUp(c.GetType(), c) Catch ex As Exception ' TODO: Some sort of error handling if important WebPortalTrace.Verbose(WebPortalTraceType.Unity, "Unity unable to build up {0}", c.GetType) End Try Next End Sub ' Get the controls in the page's control tree excluding the page itself Private Function BuildControlTree(ByVal root As Control) As List(Of Control) Dim ct As New List(Of Control) For Each c In root.Controls ct.Add(c) ct.AddRange(BuildControlTree(c)) Next Return ct End Function End Class
All you need is to put a reference into your config file:
<system.web> <httpModules> <add name="UnityHttpModule" type="Company.Product.UnityHttpModule, Company.Product"/> </httpModules> </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…
<unity> <containers> <container> <types> <type type="Company.Product.ViewModels.IRecentItemsViewModel, Company.Product" mapTo="Company.Product.ViewModels.RecentItemsViewModel, Company.Product" /> </types> </container> </containers> </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:
<unity> <containers> <container> <types> <type type="Company.Product.ViewModels.IRecentItemsViewModel, Company.Product" mapTo="Company.Product.Hotfix1.ViewModels.RecentItemsViewModel, Company.Product.Hotfix1" /> </types> </container> </containers> </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…