Thank you for reaching out to us.
But it's seems is not working in this case. Is it possible to know when user changes active document in case of CommandData plugin?
The posting you are referring to states that
MSG_DOCUMENTINFO is [...] a node message"
A little bit more precise would be to say it is an atom message, i.e., it is only being sent to
C4DAtom instances via
CommandData plugin is not an atom and its message method is part of another message stream.
I would recommend having a look at the Python Message System Manual, as it lines out how messages work, and what kind of messages to expect in
Long story short, no, you will not find a message that signals the active document having been changed to a
CommandData plugin. You will have to hook into other messages and manually check. The messages you could range from very broad as
EVMSG_CHANGE (which is being broadcasted very often) to slightly more specific message IDs like, for example
EVMSG_DOCUMENTRECALCULATED. I cannot tell you which one works best for your use case, I would have to try myself. Another approach would be to implement a
NodeData plugin and broadcast the information from there to your
CommandData. The problem is that Python lacks a good
NodeData type for that, as is lacks the
SceneHookData type which would be the natural choice in C++. You can use some of the other
NodeData types in Python like
TagData, but you should know that some atom messages are not being sent to all atoms, as Cinema 4D considers them irrelevant for these plugins.
MSG_DOCUMENTINFO is one of these messages, and it is for example not being broadcasted to
PreferenceData, which otherwise could serve as a replacement for a
SceneHookData, as it is a node which has not to be instantiated as for example an object or tag must be.