You've got a using
directive for the Microsoft.VisualBasic
namespace, but the fact that you're fully-qualifying the name Microsoft.VisualBasic.FileSystem
makes that irrelevant.
I suspect you just haven't added a reference to the Microsoft.VisualBasic.dll
assembly. (Assemblies and namespaces are very different things.)
Personally I would attempt to avoid VB-specific assemblies in the first place, to be honest.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…