Question

Just like I can set the DefaultControllerFactory to my own in the global.asax by calling ControllerBuilder.Current.SetControllerFactory() and provide a custom implementation of the factory, is it possible to somehow provide the application with my own implementation of the WebPageRazorHostFactory?

What I want to achieve is encapsulating the views in a IoC container to provide dependency injection. I’ve read the following article on Haacked: http://haacked.com/archive/2011/02/21/changing-base-type-of-a-razor-view.aspx and i think this might add to that solution.

The following doesn’t seem to work and throws an error:

Unable to cast object of type ‘ASP._Page_Views__ViewStart_cshtml’ to type ‘System.Web.WebPages.StartPage

Global.asax: (C# project)

    protected void Application_Init()
    {
        System.Web.WebPages.Razor.RazorBuildProvider.RegisterBuildProvider("cshtml", typeof(DefaultRazorBuildProvider));
    }

Class definitions: (VB Project)

Public Class DefaultRazorBuildProvider : Inherits System.Web.WebPages.Razor.RazorBuildProvider
    Private Shared _factories As New ConcurrentDictionary(Of String, Func(Of IKernel, DefaultWebPageRazorHostFactory))(StringComparer.OrdinalIgnoreCase)
    Private Shared _kernel As IKernel

    Friend Shared TypeFactory As Func(Of String, Type) = AddressOf DefaultTypeFactory

    Public Shared Function GetKernel() As IKernel
        If _kernel Is Nothing Then Throw New NullReferenceException("_kernel is not set")

        Return _kernel
    End Function

    Public Shared Sub SetKernel(ByVal kernel As IKernel)
        _kernel = kernel
    End Sub

    Public Shared Function CreateHostFromConfig(ByVal virtualPath As String) As WebPageRazorHost
        Return CreateHostFromConfig(virtualPath, Nothing)
    End Function

    Public Shared Function CreateHostFromConfig(ByVal virtualPath As String, ByVal physicalPath As String) As WebPageRazorHost
        If [String].IsNullOrEmpty(virtualPath) Then
            Throw New ArgumentNullException("virtualPath")
        End If

        Return CreateHostFromConfigCore(GetRazorSection(virtualPath), virtualPath, physicalPath)
    End Function

    Public Shared Function CreateHostFromConfig(ByVal config As RazorWebSectionGroup, ByVal virtualPath As String) As WebPageRazorHost
        Return CreateHostFromConfig(config, virtualPath, Nothing)
    End Function

    Public Shared Function CreateHostFromConfig(ByVal config As RazorWebSectionGroup, ByVal virtualPath As String, ByVal physicalPath As String) As WebPageRazorHost
        If config Is Nothing Then
            Throw New ArgumentNullException("config")
        End If
        If [String].IsNullOrEmpty(virtualPath) Then
            Throw New ArgumentNullException("virtualPath")
        End If

        Return CreateHostFromConfigCore(config, virtualPath, physicalPath)
    End Function

    Friend Shared Function CreateHostFromConfigCore(ByVal config As RazorWebSectionGroup, ByVal virtualPath As String) As WebPageRazorHost
        Return CreateHostFromConfigCore(config, virtualPath, Nothing)
    End Function




    Private Shared Function CreateFactory(ByVal typeName As String) As Func(Of IKernel, DefaultWebPageRazorHostFactory)
        Dim factoryType As Type = TypeFactory(typeName)
        If factoryType Is Nothing Then
            Throw New InvalidOperationException("Factory type not valid")
        End If



        Dim param = Expression.Parameter(GetType(IKernel))

        Dim body = Expression.[New](factoryType.GetConstructor(New Type() {GetType(IKernel)}), param)
        Return Expression.Lambda(Of Func(Of IKernel, DefaultWebPageRazorHostFactory))(body, param).Compile()
    End Function



    Public Shared Sub ApplyConfigurationToHost(ByVal config As RazorPagesSection, ByVal host As WebPageRazorHost)
        host.DefaultPageBaseClass = config.PageBaseType

        For Each import As String In config.Namespaces.OfType(Of NamespaceInfo)().[Select](Function(ns) ns.[Namespace])
            host.NamespaceImports.Add(import)
        Next
    End Sub


    Friend Shared Function CreateHostFromConfigCore(ByVal config As RazorWebSectionGroup, ByVal virtualPath As String, ByVal physicalPath As String) As WebPageRazorHost

        virtualPath = EnsureAppRelative(virtualPath)

        If virtualPath.StartsWith("~/App_Code", StringComparison.OrdinalIgnoreCase) Then
            Return New WebCodeRazorHost(virtualPath, physicalPath)
        End If

        Dim factory As DefaultWebPageRazorHostFactory = Nothing
        If config IsNot Nothing AndAlso config.Host IsNot Nothing AndAlso Not [String].IsNullOrEmpty(config.Host.FactoryType) Then
            Dim factoryCreator As Func(Of IKernel, DefaultWebPageRazorHostFactory) = _factories.GetOrAdd(config.Host.FactoryType, CreateFactory(config.Type))
            Debug.Assert(factoryCreator IsNot Nothing)
            factory = factoryCreator(_kernel)
        End If

        Dim host As WebPageRazorHost = (If(factory, New DefaultWebPageRazorHostFactory(_kernel))).CreateHost(virtualPath, physicalPath)

        If config IsNot Nothing AndAlso config.Pages IsNot Nothing Then
            ApplyConfigurationToHost(config.Pages, host)
        End If

        Return host
    End Function

    Friend Shared Function GetRazorSection(ByVal virtualPath As String) As RazorWebSectionGroup
        Return New RazorWebSectionGroup() With { _
          .Host = DirectCast(WebConfigurationManager.GetSection(HostSection.SectionName, virtualPath), HostSection), _
          .Pages = DirectCast(WebConfigurationManager.GetSection(RazorPagesSection.SectionName, virtualPath), RazorPagesSection) _
        }
    End Function

    Private Shared Function EnsureAppRelative(ByVal virtualPath As String) As String
        If HostingEnvironment.IsHosted Then
            virtualPath = VirtualPathUtility.ToAppRelative(virtualPath)
        Else
            If virtualPath.StartsWith("/", StringComparison.Ordinal) Then
                virtualPath = "~" & virtualPath
            ElseIf Not virtualPath.StartsWith("~/", StringComparison.Ordinal) Then
                virtualPath = "~/" & virtualPath
            End If
        End If
        Return virtualPath
    End Function

    Private Shared Function DefaultTypeFactory(ByVal typeName As String) As Type
        Return BuildManager.[GetType](typeName, False, False)
    End Function
End Class

Public Class DefaultWebPageRazorHostFactory : Inherits System.Web.WebPages.Razor.WebRazorHostFactory
    Private _kernel As IKernel

    Public Sub New()
        Me._kernel = Nothing
    End Sub

    Public Sub New(ByVal kernel As IKernel)
        Me._kernel = kernel
    End Sub

    Public Overrides Function CreateHost(ByVal virtualPath As String, ByVal physicalPath As String) As System.Web.WebPages.Razor.WebPageRazorHost
        Return New DefaultWebPageRazorHost(Me._kernel, virtualPath, physicalPath)
    End Function
End Class

Public Class DefaultWebPageRazorHost : Inherits System.Web.WebPages.Razor.WebPageRazorHost
    Private _kernel As IKernel

    Sub New(ByVal kernel As IKernel, ByVal virtualPath As String, ByVal physicalPath As String)
        MyBase.New(virtualPath, physicalPath)
        Me._kernel = kernel
    End Sub
End Class

Answer 1

Yes; in Web.config:

<system.web.webPages.razor>
    <host factoryType="MyProject.MyWebPageRazorHost" />
    <pages pageBaseType="MyProject.CustomWebPage">
        <namespaces>
            <add namespace="MyProject.SomeNamespace" />
        </namespaces>
    </pages>
</system.web.webPages.razor>

EDIT

To create the host in code, you can inherit RazorBuildProvider and override the CreateHost method, then register your inherited version for CSHTML and VBHTML.
In your override, you’ll need to return a WebCodeRazorHost for pages inside of App_Code.

You should download the source code; it will help tremendously.
Look in mvc3-rtm-sources\webpages\src\System.Web.WebPages.Razor.