Event Bus
Extensions often need to communicate and react to changes occuring in other extensions. For example, when a user logs in through the Authentication App, almost all of other extensions needs to update their state accordingly. Managing such inter-extension communication is done using an event bus.
In short, an event bus allows publish/subscribe-style communication between different integrations without being directly dependent to each other. Extensions can emit or subscribe to these events independently which reduces inter-extension dependency.
UIEvents Bus
UI event bus is accessible as props in root component of the integration (props.uiEvents). Currently this event bus is used to trigger UI changes such as showing/hiding the sidebar, mounting/unmounting extension-points, trigger theme change across all integrations, etc. The UI event bus is a rxjs Subject.
GlobalEvent Bus
Global event bus is accessible through the sdk (sdk.api.globalChannel). Almost all calls to the sdk APIs methods will also trigger an event on the global event bus.
The Global event bus is a rxjs ReplaySubject.
Why not using plugin system for inter-app communication?
Using the plugin system for inter-extension communication is perfectly fine but it comes with some drawbacks when compared to an event bus:
- Tight Coupling: direct api calls create a tighter coupling between extensions.
- Point-to-point Communication: Plugins usually facilitate point-to-point communication, which can be less efficient when multiple extensions need to react to the same change.
- Increased Complexity: Updates to a plugin are not automatically reflected in the view so developers still needs to come up with their own synchronization mechanisms.
- Static Contracts: Using plugins for inter-extension communication create static contracts that needs to be maintained, versioned, etc.
We will merge this 2 event buses in the future.