So you have this awesome idea for a Google Workspace Add-on (GWAO), but you need to be able to select Google Drive files and folders as a part of your process. … Ideally, you would want a built-in File Picker class that would select the files and folders from the directories you need. Whelp… unfortunately, we don’t have that right now for Google Apps Script’s Card Service.
One approach might be to build out a file picker card selecting each parent’s files and folders and navigate through it like, say, a linked list. … Instead, I decided to incorporate Googles File Picker API as a popup window from the sidebar, because, it’s kinda what it is designed for.
The Google Apps Script GDEs are publishing some very thorough tutorials just now. The latest comes from Scott Donald who has published a tutorial exploring how the Google Drive Picker can be used with Workspace Add-ons that use the Card Service. The post is particularly good at highlighting the steps required as a Google Cloud Console project.