How to get file extension at runtime/ITextBuffer.ContentType is UNKNOWN

[pmahend1]

I am developing an extension for Visual Studio for Mac. I am trying to get file content type since it will be applicable for only XML type of file extensions.

IdeApp.Workbench.ActiveDocument.GetContent<ITextBuffer>().?ContentType.DisplayName returns values like code++.xml xaml androidXml etc. But for file contents which are not assigned explicit file property (for example .csproj ,. config, .mobileconfig, .plist , .xamarin) are returning UNKNOWN

So as workaround I want to get file extension of the current active document. How can I do that? I am finding hard time understanding APIs and there is less extension. I thought if I can cast ITextView to ExtensibleTextEditor would let me get File name/File extension property but I am not getting that class through intellisense.

var textBuffer = IdeApp.Workbench.ActiveDocument?.GetContent<ITextBuffer>();
 var textview = IdeApp.Workbench.ActiveDocument.GetContent<ITextView>();
 var contentType = textBuffer.ContentType;

Please help!

[pmahend1]

I was able to get it like below

            var textdocument = textBuffer?.Properties?.PropertyList?.FirstOrDefault(x =>x.Key is ITextDocument || x.Value is ITextDocument);
            var documentvalue = textdocument?.Value as ITextDocument;

            var ext = documentvalue?.FilePath?.Substring(documentvalue?.FilePath?.LastIndexOf(".")??0);

Let me know if there is easier way.