Ubuntu – How to run an action when clicking on an appindicator

This is indeed not the intended behaviour of Application Indicators: they're meant to have one or two icons and not something that you could almost put in a widget.

There seems to be something wrong in the caching of the icon, as it should update a changed icon, though.

Anyway, you probably want to use something like 'libindicator' to create your own, custom indicator. The collection of application indicators on your panel is drawn by one indicator. You have a lot more functions at your disposal when writing a custom indicator, than when using the limited API of Application Indicators, which was limited deliberately to make sure we don't get a mess.

Also make sure to look at the package 'libindicator-tools', which contains some handy utilities for testing indicators.

I think that the need here is actually more determining of the python-appindicator library is present. If it is present, it will support all the fallback cases that you need. It will handle XFCE, KDE and older GNOME appropriately. Good example of how to do it in this answer.

The appindicator library will use DBus to check if the application indicator rendering process is available. This will be the case on Unity, or if the indicator-applet is running. If it is available it will use that, if not, it will fallback to using a GtkStatusIcon with the same menu.

Unfortunately, I believe you'd have to keep both code paths if you want to handle the case of the library not being available. Though, we'd be happy to help get the library in other distros :)