Where VSTO creates the project folder

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Julie wrote to me with a problem about where VSTO creates its DLLs and how they get trusted. Hopefully this will help ;-)

The other day I blogged about how referenced assemblies are copied around, but there's another piece to the puzzle. If you use the New Project wizard to create a VSTO project and elect to create a new document, the wizard places the document in the same folder as the project so you end up with this kind of hierarchy:

// Root project folder

C:My_DocsUserVS_ProjsProject

 

// VS Project files

  ThisDocument.vb

  Project.sln

  etc.

 

// The document

  Project.doc

 

// VS output folder

  Bin

    Project.dll

    Project.pdb

 

// VS build folder

  Obj

    Debug

      Project.dll

      Project.pdb

 

// VSTO output folder

  Project_bin

    Project.dll

    Project.pdb

In this case, VSTO will setup the security policy to trust C:My_DocsUserVS_ProjsProjectProject_binProject.dll and when you run the solution it will run the document C:My_DocsUserVS_ProjsProjectProject.doc which will try and load the assembly through the relative path .Project_bin.

If you choose to use an existing document, something a bit different happens. VSTO still creates the standard VS project hierarchy, but the Project_bin is created relative to the original document's location. You end up with something like this:

// Root project folder

C:My_DocsUserVS_ProjsProject

 

// VS Project files

  ThisDocument.vb

  Project.sln

  etc.

 

// Note: no document!

 

// VS output folder

  Bin

    Project.dll

    Project.pdb

 

// VS build folder

  Obj

    Debug

      Project.dll

      Project.pdb

 

// Document folder

C:My_DocsUserDesktop

 

// The document

  Project.doc

 

// VSTO output folder

  Project_bin

    Project.dll

    Project.pdb

In this case, VSTO builds the DLL into the project folder, but then copies it (along with any referenced assemblies) to the document's location as a post-build step. It will also setup the security policy to trust C:My_DocsUserDesktopProject_binProject.dll and when you run the solution it will run the document C:My_DocsUserDesktopProject.doc which will try and load the assembly through the relative path .Project_bin. If you try and set policy to trust the VS project location (C:My_DocsUserVS_ProjsProject*) it won't have any effect since the document / assembly is not loaded from there.

If you want to know where your assembly comes from, it's pretty easy using the CodeBase property of the Assembly object:

' Display the location of the DLL

Private

Sub

ThisWorkbook_Open

()
Handles
ThisWorkbook.Open

MessageBox.Show(Me.GetType.Assembly.CodeBase)

End

Sub

(Of course your code needs to be trusted to display this info...)