Using Kotlin Coroutines to replace LocalBroadcastManager for Firebase messaging

Question

When using Firebase Cloud Messaging on Android, it is often desirable to notify the current Activity of an incoming push notification. One of the recommended ways t

Answer 1

Coroutines don't really help with the handoff of data from one software component to another. They help with the processing multiple units of asynchronous work using syntax that appears as if they were synchronous. That's the bottom line for coroutines. They're analogous to async/await syntax in JavaScript. While you might use a coroutine to access data from asynchronous sources, it doesn't give you any primitves to proxy that data on to other components.

LiveData probably works just fine for what you're trying to do. Don't conflate ViewModel with LiveData - they solve different problems. While you're correct that ViewModel should only be accessed by code that deals with UI, that guideline doesn't extend to LiveData. It's perfectly reasonable to expose a LiveData that reflects current data from FirebaseMessagingService that is later picked up by a ViewModel, transformed, and passed on to a view. This LiveData could be a singleton, or obtained via whatever dependency injection infrastructure you choose.

Bear in mind that LiveData is really only supposed to be used for managing changes in state. It's not a "stream" of data that your app can listen to. You will need to make sure that your infrastructure is state-based in order for this to work out well. FCM itself is not state-based, but if you want your views to respond to messages from FCM, you'll need to retain enough context between each message to make sure your UI responds consistently to new messages (or the lack of messages altogether).