msgbus for collection selection in outliner

Question

I want a callback for Collection selections in the Outliner. So far I already found a common solution for object selections:

handle = object()
subscribe_to = bpy.types.LayerObjects, 'active'

def notify_test():
    print('Notify')

bpy.msgbus.subscribe_rna(
    key=subscribe_to,
    owner=handle,
    args=(),
    notify=notify_test,
)

bpy.msgbus.publish_rna(key=subscribe_to)

But what bpy.types do I subscribe to when I want a callback for collection selections? When I select a different collection in the outliner. There is:

bpy.types.LayerCollections

But there are no 'active' or 'selected' properties for this certain type.

Any help would be appreciated.

Answer 1

The msgbus is quite limited, I don't think there is a solution using that, but you can use the depsgraph_update_post application handler instead:

import bpy

def on_depsgraph_update_post(scene, depsgraph):
    selected_items = None
    area  = next(area for area in bpy.context.window.screen.areas if area.type == 'OUTLINER')
    
    with bpy.context.temp_override(
        window=bpy.context.window,
        area=area,
        region=next(region for region in area.regions if region.type == 'WINDOW'),
        screen=bpy.context.window.screen
    ):
        selected_items = bpy.context.selected_ids

    for item in reversed(selected_items):
        if isinstance(item, bpy.types.Collection):
            print("You have selected a collection:", item.name)
            return

bpy.app.handlers.depsgraph_update_post.clear()
bpy.app.handlers.depsgraph_update_post.append(on_depsgraph_update_post)