Automatic update of (Excel-DNA) XLL with Excel opened

Question

I am developing an Excel XLL Add-In using Excel-DNA and C#. The Add-In is called MyAddIn.xll. The Add-In has been saved to the users local machines, and it has been installed/added to Excel by the following procedure:

Excel Options --> Add-Ins --> Manage Excel Add-Ins --> and then adding MyAddIn.xll.

I now want to push out an update of MyAddIn.xll to all my users. I am using a deploy tool such as Salt. However, it seems like this require Excel to be closed on the users machines.

Is there a way that I can push the new xll to the users machines, when they have Excel opened, and letting the change take place when they restart Excel?

Thanks!

Answer 1

The .xll file will always be locked by Excel, so you can't update that file while the add-in is loaded. You might be able to structure your add-in so that the .xll does not change with the updates, but the .dll file(s) that you use do change.

There are two approaches the Excel-DNA supports for doing this:

1. The .dna files can redirect to subdirectories, and your root .dna file can be updated while the add-in is loaded. So you might have:

   • \AddInRoot\MyAddIn.xll
   • \AddInRoot\MyAddIn.dna
   • \AddInRoot\Version1\MyAddInImpl.dna
   • \AddInRoot\Version1\MyAddInImpl.dll
   • \AddInRoot\Version2\MyAddInImpl.dna
   • \AddInRoot\Version2\MyAddInImpl.dll

   And in MyAddIn.dna you have <DnaLibrary ...> <ExternalLibrary Path="Version1\MyAddInImpl.dna" /> </DnaLibrary>

   The while the add-in is loaded, you can replace MyAddIn.dna with a new version that refers to the new Version2 directory.

2. Excel-DNA supports loading the .dll library files without locking the .dll. So you can have: <DnaLibrary ...> <ExternalLibrary Path="MyFunctions.dll" LoadFromBytes="true" /> </DnaLibrary>

   Then you will be able to replace MyFunctions.dll even while the add-in is running.

In both cases you need not re-open Excel to load the new version, you can just File->Open the .xll file and it will reload (or call xlfRegister or Application.RegisterXLL from code).