handlers.py

import bpy
import logging

from bpy.app.handlers import persistent

logger = logging.getLogger(__name__)

_builtin_handlers = {}


# Utility functions to simplify registering bpy.app handlers
#
# Builtin handlers have to be registered and unregistered,
# call register_handlers after all modules are registered and
# vice versa when unregistering
#
# Example usage:
# from event_system import add_builtin_handler
#
# add_builtin_handler("save_pre", write_addon_version)
# add_builtin_handler("version_update", do_versioning)


def add_builtin_handler(event: str, callback):
    """
    Add to bpy.app.handlers, gets (un)registered on addon enable or disabled.
    Does not support registering handlers at runtime
    """

    global _builtin_handlers
    func = persistent(callback)
    _builtin_handlers.setdefault(event, list()).append(func)


def register_handlers():
    global _builtin_handlers
    for handler_name in _builtin_handlers.keys():
        msg = "Append <{}> builtin handlers: ".format(handler_name)

        for cb in _builtin_handlers[handler_name]:
            getattr(bpy.app.handlers, handler_name).append(cb)
            msg += "\n  - {}".format(cb.__name__)

        logger.debug(msg)


def unregister_handlers():
    global _builtin_handlers
    for handler_name in _builtin_handlers.keys():
        msg = "Remove <{}> builtin handlers: ".format(handler_name)

        for cb in _builtin_handlers[handler_name]:
            handler_list = getattr(bpy.app.handlers, handler_name)

            if cb not in handler_list:
                continue

            msg += "\n  - {}".format(cb.__name__)
            handler_list.remove(cb)

        logger.debug(msg)


def _setup_builtin_handlers():
    from .versioning import write_addon_version, do_versioning

    add_builtin_handler("version_update", do_versioning)
    add_builtin_handler("save_pre", write_addon_version)


def register():
    _setup_builtin_handlers()
    register_handlers()


def unregister():
    unregister_handlers()