Sub-controllers

Asyncio Event Hub also supports inherited event emitting, meaning you can have multiple instances of EventController that can work on different levels.

A sub-controller is just a regular controller, that will automatically emit events if it’s parent has emitted them. Eg. we could have a global event controller that has global event handlers, and beside it we could also have local controllers that have event handlers responsible for handling the same event at a more narrow scope.

Adding a sub-controller

To make a EventController a sub-controller of some other EventController, we can use the asyncio_event_hub.controller.EventController.add_subcontroller() method.

The method will not make any changes to the original (now sub) controller. We can still emit events to it and give it it’s own event listeners. The method only forces is to receive the parent’s events from the asyncio_event_hub.controller.EventController.emit() method. The sub-controller does not inherit the parent’s event listeners.

Listing 9 Adding a subcontroller

import asyncio
import asyncio_event_hub as aeh


def event_listener(a: int = 1):
    print(f"Called listener, a={a}")


async def main():
    ctrl = aeh.EventController()  # Create master controller
    sub_ctrl = aeh.EventController()  # Create subcontroller

    # Add a listener to "my_event", which always gets called
    # regardless of value a receives (no condition).
    ctrl.add_listener("my_event", event_listener)
    sub_ctrl.add_listener("my_event", event_listener)

    ctrl.start()
    sub_ctrl.start()  # Optional, as it is automatically started when added as sub-controller

    ctrl.add_subcontroller(sub_ctrl)  # Add the sub-controller

    while True:
        await asyncio.sleep(5)
        await ctrl.emit("my_event", a=10)  # Emit the event to both ctrl and sub_ctrl
        await sub_ctrl.emit("my_event", a=20)  # Emit the event to only sub_ctrl


asyncio.run(main())  # Start asyncio framework

Removing a sub-controller

A sub-controller can be removed from it’s parent by calling the parent’s asyncio_event_hub.controller.EventController.remove_subcontroller() method.

Caution

The method does not automatically stop the sub-controller. If you wish to stop it, call asyncio_event_hub.controller.EventController.stop() method manually!

Listing 10 Removing a subcontroller

import asyncio
import asyncio_event_hub as aeh


def event_listener(a: int = 1):
    print(f"Called listener, a={a}")


async def main():
    ctrl = aeh.EventController()  # Create master controller
    sub_ctrl = aeh.EventController()  # Create subcontroller

    # Add a listener to "my_event", which always gets called
    # regardless of value a receives (no condition).
    ctrl.add_listener("my_event", event_listener)
    sub_ctrl.add_listener("my_event", event_listener)

    ctrl.start()
    sub_ctrl.start()  # Optional, as it is automatically started when added as sub-controller

    ctrl.add_subcontroller(sub_ctrl)  # Add the sub-controller
    await ctrl.emit("my_event", a=10)  # Emit the event to BOTH ctrl and sub_ctrl
    ctrl.remove_subcontroller(sub_ctrl)  # Remove the sub-controller

    while True:
        await asyncio.sleep(5)
        await ctrl.emit("my_event", a=10)  # Emit the event to ONLY ctrl


asyncio.run(main())  # Start asyncio framework