How to add and use external assemblies in solutions?

Question

I need to use DocumentFormat.OpenXml.dll in my code. In the solution package, I included this external dll in the Additional Assemblies. It looks like this:

I also need to reference it, so that I can use its classes in the code. So I added a reference to the same file. But now, when I want to deploy my solution it shoots error with the message:

"SharePointProject" and "SharePointProject" contain a file that deploys to the same Package location: DocumentFormat.OpenXml.dll

I guess the problem is that I haven't referenced the dll from additional package assemblies list, but directly from the file, though I could be wrong here.

How do I make sure that the external assembly DocumentFormat.OpenXml.dll gets deployed with the solution and I can use its classes in my code? Thanks!

Answer 1

Your problem may be related to incorrect locations of SharePoint Project Items (SPI). After you add your assembly click on Show All Files in the Solution Explorer in Visual Studio and locate the SharePointProjectItem.spdata file. Open it and make sure that the Target attribute of all the ProjectItemFileSource elements points to the correct location.