id like to trap a callback on a multiparm list when items are
added/removed/cleared etc… unlike other params, this container
doesnt have a callback field. Is there some other way to register
a callback on the container to manage it, or do you have to drive
global management whenever one of its template params are
modified?

hacks?

Unfortunately there isn't any way to do this. From an old email about such an RFE:

This is an existing RFE, (ID# 30076). However, it is a very difficult RFE for us to accomplish because it has never been possible to associate a callback with a multiparm, even in C++. There is no way to set the PRM_CALLBACK type on the PRM_Template, and no argument to the constructor for setting the callback information.

The only kind of hack I can think of off the top of my head for something similar would be to have a button that does it manually. You would have to keep track of a list of multiparm instances through a parameter name or something and when you make a change hit a button that calls code to figure out what was added/removed based on what indicator parms are left and what is stored on the list, then try and handle the change.

I had a similar issue

I did not want the artists to need to remember to press an update button so:

I created an integer with the callback attatched
i put a channel expression in the mutiparm block referencing my int parm
i then hid the multiparm

hey presto - the great thing is you still see all of the parms in the multiparm block!

hope that helps