c# - Acessing currently opened solution in a vsix project -

i want access path open solution in visual studio vsix project. how can that?

this thread tells if solution open or not gives nothing path of opened solution

i use this:

    public string getinitialfolder(dte dte)     {         if (!dte.solution.isopen)             return null;         return system.io.path.getdirectoryname(dte.solution.fullname);     } 

but expect error, cannot return path!