Make your app work perfectly off— Connection Interrupted

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

Transcript

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3. @jeremybbonze
   Android Engineer at WorkWell
   @xgouchet
   Lead Android Engineer at WorkWell
   

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11. “Do not treat Offline as an error condition.
    Offline is the default state, Online is icing on the cake.”
    

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12. accessibility /əksɛsɪˈbɪlɪti/ n.
    ● the quality of being able to be reached or entered.
    ● the quality of being easy to obtain or use.
    

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21. ✓
    

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22. ✗
    

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24. ✓
    

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27. ✓
    

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28. ✓
    

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30. data class Item (
    // …
    val lastModified: Long,
    val timeToLive: Long
    )
    

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31. interface ItemRemoteSource {
    fun get(id: String): Single
    fun getAll(): Single>
    }
    interface ItemRemoteSink {
    fun create(item: Item): Single
    fun update(item: Item): Single
    fun delete(id: String): Single
    }
    

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32. interface ItemLocalSource {
    fun get(id: String): Single>
    fun getAll(): Single>>
    }
    interface ItemLocalSink {
    fun create(item: Item): Single
    fun update(item: Item): Single
    fun delete(id: String): Single
    }
    

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33. sealed class LocalResult {
    abstract fun get(): T
    class Present(private val value: T): LocalResult() {
    override fun get(): T = value
    }
    class Obsolete(private val value: T): LocalResult() {
    override fun get(): T = value
    }
    class NotFound: LocalResult() {
    override fun get(): T =
    throw Resources.NotFoundException("No value")
    }
    }
    

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34. interface ItemGlobalSource {
    fun get(id: String): Single
    fun getAll(): Single>
    }
    interface ItemGlobalSink {
    fun create(item: Item): Single
    fun update(item: Item): Single
    fun delete(id: String): Single
    }
    

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35. fun Observable>.flatMapOfflineFirst(
    fallback: RemoteSource.() -> Observable,
    update: LocalSink.(O) -> Observable
    ): Observable {
    return flatMap { result ->
    when (result) {
    // …
    }
    }
    }
    

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36. return flatMap { result ->
    when (result) {
    is LocalResult.Present -> Observable.just(result.get())
    // …
    }
    }
    

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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())
    }
    }
    // …
    }
    }
    

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38. return flatMap { result ->
    when (result) {
    // …
    is LocalResult.NotFound -> {
    if (networkWatcher.isNetworkAvailable()) {
    remoteSource.fallback()
    .flatMap { localSink.update(it) }
    } else {
    Observable.empty()
    }
    }
    }
    }
    

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39. fun List>.keepPresentOnly()
    : LocalResult> {
    return LocalResult.Present(
    filter { it is LocalResult.Present }
    .map { it.get() }
    )
    }
    

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40. fun LocalResult>.notFountIfEmpty()
    : LocalResult> {
    return if (this is LocalResult.NotFound || get().isNotEmpty()) {
    This
    } else {
    LocalResult.NotFound()
    }
    }
    

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41. fun List>.allPresentOrNone()
    : LocalResult> {
    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()
    }
    })
    }
    }
    

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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()
    }
    }
    }
    

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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
    }
    

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47. ● Same pagination logic on Remote and Local source
    

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49. ● Balance between disk usage / available data
    ● Only deals with part of the problem
    

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50. ● They do actually mean something
    ● 404 (NOT FOUND) or 410 (GONE) → delete locally
    

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51. ● Request (once in a while) recently deleted items
    ● Use a Hash / Timestamp to only get the relevant changeset
    

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53. ● The main solution to handle offline actions is to schedule jobs
    

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54. ● JobScheduler
    ● Android-Job (Evernote)
    ● JobDispatcher (Firebase) [Deprecated]
    ● WorkManager
    

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55. ● Set syncStatus in local DB
    ● Launch sync job as an internet connection is back
    ● Once remote and local DB are synced, update syncStatus
    

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56. data class Item (
    // …
    val lastModified: Long,
    val timeToLive: Long,
    val syncStatus: SyncStatus
    )
    enum class SyncStatus {
    TO_BE_SYNCED, SYNCED
    }
    

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59. ✓
    

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61. “Do not treat Offline as an error condition.
    Offline is the default state, Online is icing on the cake.”
    

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62. ● Measure your network usage
    ● Test your own application with lousy network conditions
    ● Test your own application in airplane mode
    ● Use your own application
    

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63. ● Offline First Slack Community
    ○ http://offlinefirst.org/chat/
    ● Offline resources and articles
    ○ https://medium.com/offline-camp/
    ○ http://offlinefirst.org/
    

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