New Excel Add-in & Side Loading

I recently published a new Excel Add-in called “Excel Send to Trello.” It is a pretty nifty add-in that will take an Excel sheet full of names, descriptions, and dates and build a bunch of Trello Cards on a specific list in Trello for you. It is just a start (v1.0) and has many features to come based on popularity.

But when I submitted the add-in to AppSource they came back to me with an issue that I was not seeing. Specifically, that the icon on the Ribbon was showing the default add-ins image and not my icon. I did not see this on my “beta” test site that I was using but had sent them a link to my manifest with was right to my production published version. The issue it turns out after a lot of testing was the .htaccess on my production site and the ONLY difference was this line:

<IfModule mod_headers.c>
    Header set Cache-Control "no-store, no-cache, must-revalidate"
</IfModule>

The problem it turns out is that Excel (full client) cannot read your icon without caching it. This works FINE in Excel Online. Oh well. So, I cannot prevent my add-in JS files from being cached which it turns out is a huge problem when I push an update it can take days/weeks for the Office application to expire its own cache. Unless someone know a way around this…

Anway, the way I discovered this was via sideloading the manifest pointing to my production site. And it also turns out I had forgotten how EASY Outlook makes sideloading. In Excel (full client) it is not that easy, because you do not have the option to point to your own manifest, except in Excel Online. Then I recall some work a colleague Marty Andren and I worked on many, many years ago, called the Web Add-in Side loader. And low and behold, it still works like a charm.

I was able to sideload in Excel using the command line tool, then I saw the problem. That is where I began the file-by-file comparison “Beta” to “Production” and found the difference mentioned above.

Anyway, it was an adventure, with a blast from the past! And keep an eye out, my new Excel Add-in will hopefully be published any day now.