How can I implement Paging library 2 Boundary Callback using Coroutines?

Question

I want to implement my custom PagedList.BoundaryCallback with coroutines, liveData and repository pattern using Paging Library 2, but I couldn't find a good example of integration of these libraries.

Even in Android official samples, they use enqueue and callbacks to perform the API request with paging 2...

I read this Medium post also but it use a coroutines scope inside the boundary callback and I think that is not a good practice.

Is there any way to achieve it? Or should I migrate to Paging 3?

You can use `suspendCancellableCoroutine` or `suspendCoroutine` to convert `enqueue` calls into suspend functions. And you can use `callbackFlow` to convert callbacks that get called repeatedly into Flows that you can collect in coroutines. I don't use Paging so can't write a proper answer. The above should be enough for you to Google some examples of how to do these conversions. Though if you're going through the trouble of migrating to coroutines, I don't see why you wouldn't migrate to the latest paging library as well. — Tenfour04, Aug 30 '21 at 16:03
I don't know much about the specific paging library, but it's clearly stated on the version 3 that they added first class support for Kotlin coroutines, so I would honestly go for upgrading if that's an option for you. If not, then yes you can use the techniques mentioned by @Tenfour04 — Joffrey, Aug 30 '21 at 18:13

score 0 · Accepted Answer · answered Sep 01 '21 at 15:38

This solution works for me:

I injected a CoroutinesDispatcherProvider in my Repository:

class MyRepository @Inject constructor(
    private val remoteDataSource: MyRemoteDataSource,
    private val localDataSource: MyDao,
    private val coroutinesDispatcherProvider: CoroutinesDispatcherProvider
 ) {...}

Then inside my repository, I passed this provider to my boundary callback:

private val boundaryCallback =
    MyBoundaryCallback(remoteDataSource, localDataSource, coroutinesDispatcherProvider)

fun getList(): LiveData<PagedList<MyModel>> = LivePagedListBuilder(
    localDataSource.getAll(),
    pagedListConfig
).setBoundaryCallback(boundaryCallback).build()

And finally, I use this dispatcher in my boundary implementation to launch my request from repository:

private val ioCoroutineScope by lazy {
   CoroutineScope(coroutinesDispatcherProvider.io)
}

override fun onZeroItemsLoaded() {
    ioCoroutineScope.launch {
        remoteDataSource.getList()
    }
}

How can I implement Paging library 2 Boundary Callback using Coroutines?

1 Answers1