ReaktivePager

ReaktivePager is a Kotlin multi-platform library that helps handle paginated results in a reactive way.

It is based on this gist from @mttkay. It uses Reaktive by @badoo as the backing Rx library.

Installation

Add Bintray repository into your root build.gradle file:

repositories {
    maven {
        url  "https://dl.bintray.com/doublesymmetry/maven"
    }
}

Add publication:

implementation 'com.doublesymmetry:reaktive-pager:<latest-version>'

Usage

There's two ways to use this library: You can either create a Pager instance or use the observablePage method to create a paginated Observable.

1) Creating a Pager instance

The Pager class contains an attribute pager that you can subscribe to. This will trigger onNext with the first page, and will continue to giving you the next page whenever you call Pager.next(). It will trigger onComplete when there is no more results to load.

2) Using the observablePage method to create an Observable

The method will return an Observable can subscribe to. This will trigger onNext with the first page, and will continue to giving you the next page whenever the given trigger is fired. It will trigger onComplete when there is no more results to load.

Examples

Using Pager

typealias Page = List<Int>

class SomePresenter {
    private val fetchNextTrigger = PublishSubject<Unit>()

    val pager: Pager<Page> = Pager(
        nextPage = {
            val last = it?.lastOrNull() ?: 0
            observableOf(listOf(last + 1, last + 2, last + 3))
        },
        hasNext = {
            val last = it.lastOrNull() ?: return@Pager true
            return@Pager last < 10 // arbitrary condition for the demo
        }
    )
}

// ...

pager.page.subscribe(onNext = { Log.d(it) })
// print [1, 2 ,3]

pager.next() // print [4, 5, 6]
pager.next() // print [7, 8, 9]
pager.next() // print [10, 11, 12]

Using observablePage

typealias Page = List<Int>

val nextPage: (Page?) -> Observable<Page> = nextPage@ {
    val last = it?.lastOrNull() ?: 0
    return@nextPage observableOf(listOf(last + 1, last + 2, last + 3))
}

val hasNext: (page: Page) -> Boolean = hasNext@ {
    val last = it.lastOrNull() ?: return@hasNext true
    return@hasNext last < 10 // arbitrary condition for the demo
}

val fetchNextTrigger = PublishSubject<Unit>()

val page = observablePage(nextPage, hasNext, fetchNextTrigger)

// ...

page.subscribe(onNext = { Log.d(it) })
// print [1, 2 ,3]

fetchNextTrigger.onNext() // print [4, 5, 6]
fetchNextTrigger.onNext() // print [7, 8, 9]
fetchNextTrigger.onNext() // print [10, 11, 12]

Coroutines interop

Reaktive recommends to avoid using Ktor in Kotlin/Native multithreaded environment until multithreaded coroutines, but if you really need to use it we've provided a helper observableFromCoroutineUnsafe that you can use in your nextPage declaration.

typealias Page = ...

class SomePresenter {
    private val page: Observable<Page> = {
        val nextPage: (Page?) -> Observable<Page> = {
            // Dispatcher should be defined per platform
            observableFromCoroutineUnsafe(Dispatcher) {
                return@observableFromCoroutineUnsafe ...
            }
        }

        val hasNext: (page: Page?) -> Boolean = { it?.hasMore == true }

        observablePage(nextPage, hasNext, trigger)
    }()
}

// ...

page.subscribe(onNext = { Log.d(it) })