Blender Addon: Copy Collection Custom Properties to Collection Instance

blender-copy-collection-props.py

# work-around for https://projects.blender.org/blender/blender/issues/140819

bl_info = {
    "name": "Copy Collection Custom Properties",
    "description": "Copy Collection custom properties when Collection instances are created",
    "author": "David M. Lary",
    "version": (0.2,4),
    "blender": (2, 80, 0),
    "category": "Development"
}

import bpy, _bpy
from bpy.app.handlers import persistent

# Keep track of known objects
known_objects = set()

@persistent
def copy_collection_properties(scene):
    global known_objects

    # pull the list of current objects, and get the list of new objects from it
    current_objects = set(obj.name for obj in bpy.data.objects)
    new_object_names = current_objects - known_objects

    # replace the known objects list because one may have been removed
    known_objects = current_objects

    # iterate through new objects, for the collection instances, copy the
    # custom properties from the collection to the instance object.
    for name in new_object_names:
        obj = bpy.data.objects.get(name)
        if not hasattr(obj, "instance_type") or obj.instance_type != 'COLLECTION':
            continue
        col = obj.instance_collection
        # print(f"copy collection properties: {name}")
        for key in col.keys():
            obj[key] = col[key]

@persistent
def on_file_loaded(_path):
    # update the known object list
    global known_objects
    known_objects = set(obj.name for obj in bpy.data.objects)

def register():
    # Use unrestricted data to get the current object list.
    # If we don't do this, the first time we add an object, we'll overwrite any
    # existing values
    global known_objects
    known_objects = set(obj.name for obj in _bpy.data.objects)

    if copy_collection_properties not in bpy.app.handlers.depsgraph_update_post:
        bpy.app.handlers.depsgraph_update_post.append(copy_collection_properties)
    if on_file_loaded not in bpy.app.handlers.load_post:
        bpy.app.handlers.load_post.append(on_file_loaded)

def unregister():
    if on_file_loaded in bpy.app.handlers.load_post:
        bpy.app.handlers.load_post.remove(on_file_loaded)
    if copy_collection_properties in bpy.app.handlers.depsgraph_update_post:
        bpy.app.handlers.depsgraph_update_post.remove(copy_collection_properties)