Sub ToggleAspNetCodeBehindFile()
    'Add file extensions here
    Dim langExtension() As String = {".cs", ".vb", ".jsl"}
    Dim activeDoc As String
    Try
        activeDoc = LCase(ActiveDocument().FullName)
        If (InStr(activeDoc, ".aspx") Or _
            InStr(activeDoc, ".ascx") Or _
            InStr(activeDoc, ".asmx") Or _  
            InStr(activeDoc, ".asax")) Then
            ' Add additional file extensions here
            Dim i As Integer
            Dim isCodeBehind As Boolean = False
            Dim extensionLength As Integer = 0
            For i = 0 To langExtension.Length - 1
                If activeDoc.EndsWith(langExtension(i)) Then
                    isCodeBehind = True
                    extensionLength = langExtension(i).Length
                    Exit For
                End If
            Next
            If (isCodeBehind) Then
                OpenAspNetFile(activeDoc, extensionLength)
            Else
                OpenCodeBehindFile(activeDoc)
            End If
            Exit Sub
        End If
        Catch
            MsgBox("Please select an ASP.NET document to toggle.", _
            MsgBoxStyle.OKOnly, "No ASP.NET Document Selected")
        End Try
End Sub

'Description: Opens an aspx, ascx, asax file
Private Sub OpenAspNetFile(ByVal activeDoc As String, _
    ByVal extensionLength As Integer)
    Dim fileName As String
    Dim projItem As ProjectItem
    ' .asax or .asmx file
    ' Close document if in design mode and open code view
    If (InStr(activeDoc, ".asax") Or InStr(activeDoc, ".asmx")) Then
        If (InStr(DTE.ActiveWindow.Caption, "design", _
        CompareMethod.Text)) Then
            ActiveDocument.Close(vsSaveChanges.vsSaveChangesPrompt)
        End If
        projItem = DTE.Solution.FindProjectItem(activeDoc)
        projItem.Open(Constants.vsViewKindCode).Activate()
    Else
        fileName = Left(activeDoc, activeDoc.Length - extensionLength)
        Try
            projItem = DTE.Solution.FindProjectItem(fileName)
            projItem.Open(Constants.vsViewKindTextView).Activate()
        Catch
            MsgBox(ActiveDocument().Name & " is not a valid " _
            & "Code-Behind file.", MsgBoxStyle.OKOnly, _
            "ASP.NET file not found")
        End Try
    End If
End Sub

'Description: Opens the code behind file
Private Sub OpenCodeBehindFile(ByVal activeDoc As String)
    Dim projItem As ProjectItem
    projItem = DTE.Solution.FindProjectItem(activeDoc)
    projItem.Document.DTE.ExecuteCommand("View.ViewCode")
End Sub