Make your app work perfectly off— Connection Interrupted

As developers, more often than not, you have access to fast and reliable internet connection, all day long. But the users you target won't. Limited data plans, unreliable network coverage, commuting : those are real obstacle that your users will see daily. This means that network will only be available at some times, and not necessarily when the user wants to interact with your application.

An introduction to offline first development on Android, given with Jérémy Bartolomeu Bonze

Transcript

3. @jeremybbonze Android Engineer at WorkWell @xgouchet Lead Android Engineer at WorkWell
11. “Do not treat Offline as an error condition. Offline is the default state, Online is icing on the cake.”
12. accessibility /əksɛsɪˈbɪlɪti/ n. • the quality of being able to be reached or entered. • the quality of being easy to obtain or use.
21. ✓
22. ✗
24. ✓
27. ✓
28. ✓
30. data class Item ( // … val lastModified: Long, val timeToLive: Long )
31. interface ItemRemoteSource { fun get(id: String): Single<Item> fun getAll(): Single<List<Item>> } interface ItemRemoteSink { fun create(item: Item): Single<Item> fun update(item: Item): Single<Item> fun delete(id: String): Single<Boolean> }
32. interface ItemLocalSource { fun get(id: String): Single<LocalResult<Item>> fun getAll(): Single<List<LocalResult<Item>>> } interface ItemLocalSink { fun create(item: Item): Single<Item> fun update(item: Item): Single<Item> fun delete(id: String): Single<Boolean> }
33. sealed class LocalResult<T> { abstract fun get(): T class Present<T>(private val value: T): LocalResult<T>() { override fun get(): T = value } class Obsolete<T>(private val value: T): LocalResult<T>() { override fun get(): T = value } class NotFound<T>: LocalResult<T>() { override fun get(): T = throw Resources.NotFoundException("No value") } }
34. interface ItemGlobalSource { fun get(id: String): Single<Item> fun getAll(): Single<List<Item>> } interface ItemGlobalSink { fun create(item: Item): Single<Item> fun update(item: Item): Single<Item> fun delete(id: String): Single<Boolean> }
35. fun <O> Observable<LocalResult<O>>.flatMapOfflineFirst( fallback: RemoteSource.() -> Observable<O>, update: LocalSink.(O) -> Observable<O> ): Observable<O> { return flatMap { result -> when (result) { // … } } }
36. return flatMap { result -> when (result) { is LocalResult.Present -> Observable.just(result.get()) // … } }
37. return flatMap { result -> when (result) { is LocalResult.Obsolete -> { if (networkWatcher.isNetworkAvailable()) { remoteSource.fallback() .flatMap { localSink.update(it) } .startWith(result.get()) } else { Observable.just(result.get()) } } // … } }
38. return flatMap { result -> when (result) { // … is LocalResult.NotFound -> { if (networkWatcher.isNetworkAvailable()) { remoteSource.fallback() .flatMap { localSink.update(it) } } else { Observable.empty() } } } }
39. fun <T : Any> List<LocalResult<T>>.keepPresentOnly() : LocalResult<List<T>> { return LocalResult.Present( filter { it is LocalResult.Present } .map { it.get() } ) }
40. fun <T : Any> LocalResult<List<T>>.notFountIfEmpty() : LocalResult<List<T>> { return if (this is LocalResult.NotFound || get().isNotEmpty()) { This } else { LocalResult.NotFound() } }
41. fun <T : Any> List<LocalResult<T>>.allPresentOrNone() : LocalResult<List<T>> { return if (isNotEmpty() && all { it is LocalResult.Present }) { LocalResult.Present(map { it.get() }) } else { LocalResult.Obsolete (mapNotNull { if (it is LocalResult.NotFound) { null } else { it.get() } }) } }
45. abstract class PaginationScrollListener( private val srLayout: SwipeRefreshLayout, private val onLoadNextPage: () -> Unit ) : RecyclerView.OnScrollListener() { override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) { super.onScrolled(recyclerView, dx, dy) if (isLastItemVisible() && !isFirstItemVisible() && !srLayout.isRefreshing) { onLoadNextPage() } } }
46. override fun loadNextPage(context: ContextC, currentListSize: Int) { val pageToLoad = computePageToLoad(currentListSize) if (pageToLoad >= 0) { loadPage(context, pageToLoad, false) } } private fun computePageToLoad(currentListSize: Int): Int { val remainder = currentListSize % PAGE_SIZE val pageCount = (currentListSize - remainder) / PAGE_SIZE return if (remainder > 0) -1 else pageCount + 1 }
47. • Same pagination logic on Remote and Local source
49. • Balance between disk usage / available data • Only deals with part of the problem
50. • They do actually mean something • 404 (NOT FOUND) or 410 (GONE) → delete locally
51. • Request (once in a while) recently deleted items • Use a Hash / Timestamp to only get the relevant changeset
53. • The main solution to handle offline actions is to schedule jobs
54. • JobScheduler • Android-Job (Evernote) • JobDispatcher (Firebase) [Deprecated] • WorkManager
55. • Set syncStatus in local DB • Launch sync job as an internet connection is back • Once remote and local DB are synced, update syncStatus
56. data class Item ( // … val lastModified: Long, val timeToLive: Long, val syncStatus: SyncStatus ) enum class SyncStatus { TO_BE_SYNCED, SYNCED }
59. ✓
61. “Do not treat Offline as an error condition. Offline is the default state, Online is icing on the cake.”
62. • Measure your network usage • Test your own application with lousy network conditions • Test your own application in airplane mode • Use your own application
63. • Offline First Slack Community ◦ http://offlinefirst.org/chat/ • Offline resources and articles ◦ https://medium.com/offline-camp/ ◦ http://offlinefirst.org/