In Visual Studio (2013/2015/2017), the Document Outline window for C# files is always empty ("There are no items to show for the selected document."). It seems that this functionality is not (not yet / no more) implemented.
But then, how do I view the structure of the file? Is there any extension which implements this functionality?
Using the Solution Explorer and Class View are NOT the solution. In the old Visual Studio 2003, I did use a self written Add-In, because it was easy to read the structure. (There were also other tools but I cannot find them anymore). So I ask here which solution you know. :-)
EDIT: Similar question also found: How to show code outline in Visual Studio?