How can I detect whether something is selected in Dolpin's right pane?

[meven]

@adeptus

Maybe there exists some boolean value which changes when selection is empty and which can be read via qdbus, for example?

The selection will never be accessible through dbus. That’s on purpose.
That’s a security hazard if any program can poke at the current files you are working on in dolphin.

@meven

That’s an API weakness, we need to allow to differentiate 1 file selected from the current workding directory, and expose this to ServiceMenus.

This.
We would need a new option as X-KDE-MinNumberOfUrls, something like X-KDE-IgnoreCWD X-KDE-SkipCurrentWorkdingDirectory.