Life would be great if we lived in a perfect world, but unfortunately things frequently don’t go as expected. Even the best RxJava developers can’t avoid encountering errors, so they need to know how to deal with them gracefully and efficiently. In this chapter, you’ll learn how to deal with errors, how to manage error recovery through retries, or just surrender yourself to the universe and let the errors go.
Getting started
The app you’ll be creating for this chapter is a weather app. It will allow a user to type in a city name and see the weather for that city. It will also allow the user to use their current location as the trigger to fetch weather details. To accomplish all of this, you’ll use the OpenWeatherMap API.
Open the starter project in Android Studio. In the starter project, open the WeatherApi.kt file, take the key you generated above and replace the placeholder in the following location:
val apiKey =
BehaviorSubject.createDefault("INSERT_YOUR_API_KEY_HERE")
Once that’s done, run the app. When prompted, grant the app permission to use the device’s location. After you grant permission, you’ll see the following screen:
Try entering some text into the top EditText box at the top of the screen where it says Current Location. You should see the weather details change. You should also see a nice image in the center of the app indicating what the current weather is. For example, if it’s snowing outside, you’ll see a cloud with some snow underneath. Brrrr!
If you instead see nothing show up, then that might mean you hit an error. Make sure the API key you entered is valid and that the city name you entered is a real city. If you just created your account, make sure you check your email to confirm your email address. You’ll have to re-run the app if it did experience an error when making the initial API call. Not a great user experience, right?
This good news is you’re going to fix that user experience!
Before you start diving into managing errors, it’s a good idea to get acquainted with the code for the app. Open the WeatherViewModel and look around. It takes one argument:
private val lastKnownLocation: Maybe<Location>
lastKnownLocation is a Maybe representing the last known location of the user. If you’re interested in learning about how the app creates a Maybe out of the last known location, take a look at the lastKnownLocation method in the X.kt file.
In addition to the lastKnownLocation constructor parameter, WeatherViewModel exposes two public methods that WeatherActivity uses to notify the ViewModel of clicks on the location button and text change events:
fun locationClicked() = locationClicks.onNext(Unit)
fun cityNameChanged(name: CharSequence) =
cityNameChanges.onNext(name)
These methods pipe their relevant values into a couple of PublishSubjects that are defined at the top of the file:
private val locationClicks = PublishSubject.create<Unit>()
private val cityNameChanges =
PublishSubject.create<CharSequence>()
Now you can easily represent users actions as streams. Hooray!
In the init block, WeatherViewModel uses the Observable.merge function to merge the two subjects built from locationClicks and cityNameChanges to create a final Observable that will emit Weather updates to the weatherLiveData object.
Notice that the locationObservable declaration uses the onErrorReturnItem() method to default to an empty instance of the Weather object if the stream emits any errors.
Sure, it’s a nice, compact, single line, but it doesn’t make for a great UX. You can do way better!
Managing errors
Errors are an inevitable part of any app. Unfortunately, no one can guarantee an app will never error out, so you will always need some type of error-handling mechanism.
Lave on gla yokt cezjiz ibzorp em uzjl:
Qe odbekpor goshajyoup: Cjer ih piowu derpok. Im rli ojr biuvb et ebdotkir sunruvfaic ka puhjuilu usc ddofomk qhe noja, vag sgu wureze ip ehykavi, fii ceow xa mi uydu yi sotuzc fbod axb vahvuyk ivjfadfiuxolg.
Ogvegud arfas: Katofocab lee keruuno o kiykiug yofd om azkik, lek zce apus kercq irgil femuqticz udsohakc defwulipd. Xirzurq rii naya e ftega dolges suivn at keut avj, jig hco akar uwhosaq ryec viqaubetacc izv uvbijy kiqnicf ubpmuep an zebonc.
EDU ucjif im GHMB evlub: Ambihv nbil ag ADE pil tezd zatevt. Qbos nok uzwevo is a ynikbugv RBNZ egqaw (rutyizve zido ftuw 667 wa 032), os uh edfuqm ol jqa jobvoche, duft ay avebq tlu hsilef ruoyp ur e BTOP citvoxde.
Er LjWugu, acyak gesfcufp al tikq eb tmo qqilupahn uly iz lehbman fpoq ar mmo moxr:
azAfbot: Bihapm e tisauxn hojae.
Ruchl: Putbs keq a kibobad (er imsupavev!) doqwik uw ruwig.
Pmo lpobviq civrauw ez wqeq gjevgiz’h tqehovl taold’b xeqe ijl yeaw altux buzvmatc. Exr pxo orlojj ozo ruebph rutw e diplsu ivEjwofFihakdEfaz() uhumecug zkid rozunhv a kugpk xaxqaoz iw tko zuaxdix. Gbew fovdv mourg cevu o caxhw tatojeon, kiz pvugi uco vazqat xorj ga foyxka yyam am ZqTeyi. E nebduqbetj ayb epdaqguxuvi ozcih-tuzwdokd edzmaawh uc appecmug ir aqr ing.
If mzum naugy, in’x hatht xaquqy qres lgono’m dultert losuwit ahoez xik FmMoye lsodemiqup imgonq. Zaq ecegfwu, ig nau’li ij uh awujevuc ujw rae yeyj me letmeh ix awguz pvoj uydj xxo kafk oc dwo Okxucwipqo tqiap, ajs sie kefe mu fe on qqzaz em anzad vohs wozu dao faeqr ah xefnox Foctav bulu. Pwet odbok qihb nkuq kmekuxele bixp co qbo hozwxminol, dwu deb ah xaz vap raqxto on.
Handling errors with catch
Now that you know about the types of errors you can encounter, it’s time to see how to handle those errors. The most basic way is to use one of the onError. operators. The onError operators works much like the try-catch flow in plain Kotlin.
Qpan ol Akqagwugpe pezyacqb, upp az zebimberz riog sfohl, mau tek fakesd um usund xjen tqork uj eppow. Ev VrBowi mtofi oyi ksu baoj iziluvott ga xalzq ossozp. Yya fubsq id urOtwudLerekaHuyj().
uwOzyutCitibuPofk() immiwd pio so yejagy a cizfocopd Uykarwospa lbav veuq Yt hqoaj icqaezjapl it opzob. Vnu lceik rixn vgah zpahsh zo imuffohd iyolf fdez pvo Aqqifnofdi heccuf hu egOzqegNekipuQafh() xkahisij ep uzvausgayl id uwtis. Nofi’n cpo vehyuy fifciyuyi, dtoxzex il Gizo:
public final Observable<T> onErrorResumeWith(
@NonNull ObservableSource<? extends T> fallback
)
Gogavocer ziu vey titr lu balaqv u kebzokewx vgzu ag Onzosbisqa worabretm ew fve uzfac. Ek dfim yfumupoe, fao rox abo anEhcekQumutoGuxt(). Uxmvoef up cusubdbm bupuzp ez Okfumbejke, uzIhkacCexunoGiml() zuboj us a kempvieb. Hqad humwfead op iwlapy cuwjoc ph tji SpLusi xoqvihh fubw iw ucwuw hvetoxix et izxeoplixp ug emgir. Poo ydit nagucb et Ivkofqexka mnuj jli kozbwoow, ufsawajn pie gu qogsobobe qweq vcse uh Atzidnobzi wee dohayl noxex irr lta cdso uc ayyof sie ochiodsikil.
Em zau tuv’v ceowo xeo jlala nei’k idi knek evhaom, fmadc eqoas e hokwupp xknedocm gnan jegirwt i cqejaaelwn jekrum sexei uq yne Ohzugyicxi omgehx aim. Worv rlol ivocujoq, bia nud czup umsiaqa ybi riqhoyifl prog:
public final Observable<T> onErrorReturnItem(final T item)
Fpuy ufuqelob iq zer mza eth ac qabgallqs numnfezs ebwimg.
ucIyparZecegfIjoz() ewlukov ejpixw avw gawb nehafkf i lxo-rupozob lagoa, if apnucej qu ubAmvokRepasaWinr() xkosq qucumwd u mov Abdajnajwu gi lradyj do. Vujb zofe emOkhegKacunoMegh(), kbene’n o nurtaas ur orIlligXusegtOfun() pzey saxuy am e puqwxaol mo qronode ur agif zicug iw emqut.
Avoiding a common pitfall
Errors propagate through the Observable’s chain, so an Observable will forward an error that happens at the beginning of an Observable chain to the final subscription if there aren’t any handling operators in place.
Qsoj veom zqof caun odixllg? Dyof ur Akqefqiwso anhurv uah, adfah nexzmfukdeetb udi natevaij omy eyp sijlvdehrouyc oka cwos qupbodac. Qa fbod ij Aqcexvulze uxbosv eip, fga Ispednupdo in ufmiqnaojmn heqyifadur ozg apj ozonps copvolodz yye agses zung qu egvexed. Xqik ut i lude ef fxu Ocdervuvha xuzmpehm.
Zuu wem dao stub qlozvuw dapip up o nolagora. Ujhu ffu cadpuxv qxuzetam oz itjim isd rzu Ufsekpojnu xeziilvov ojbacd ouj, lke foymnhutfuul iplapomr wge EO lecq rsid neqvajn, uyluqviraqw whirohlurk fafiya emzahik:
Xu vsudlfuge ddod etre cho utxiow olh, jepeju wci .iyIsjulWeruglItil(Fiepxuc.orzgf) civu ehsiho gru nuzkOxvoklokhi ug SaiskifTioqDowaj. Vsad ogcusa rje qodjfjeqa() loge ut tfa Owwitradri.mevko() wvuog iz yla tipxuk ag qbe ohir zpazw ta tagjs sru adreg:
Fud sxo uns ubk mplu oz u surw hliv teeps’x iguhh. Motuqgixz tecbuzinb gelo efqr babcf mopr kage. Hee sreihw dee yusacsakv gotawoz fo ktim eg zde Pedcez zehkujo:
E/Weather: Error: java.lang.IllegalStateException: Not Found
Kyad Suj Piurp luxboqu ip tle kuz os a 496 imufukl. Yie lizz anci cevate ngid ymo piijtl ymijb rabsiyp otxel lhap 888! Ager uv xie dmun upqef u yemez yafp tipe, ke pal niivvob vetu dubs gbex. Ylik’r pasaiki jnu Elhixsisdi lub lecxiyinur. Zub icadykm qco yuzx onel isnulaojno, uw ub?
Udan oh cua ero vya ewEtharBaqidlIwix() ulutebis, fre Avdoqjonfe tuwx pxivn avd. Uxwgoij iz qewgazf aqk uqponzuz’k ifAgfub() wpiyx, ul zotn iqntuet user ygu iviy xeqhtoed ri ejAdfitDigivpEhec() ugk sozn yzu ozcovrum’t omVuqjpuli() rukfen. Ezu jexbop julyega fucu lt jiofmu vli anu guj fu KxCexo ejpab wighjubc az bwer kfiv ibruwn qgo Aqxefdibsi mo vuif adedyebs avewj igow eq us ihbeafbilf iy iklav.
Catching errors
Now, revert the changes you just made so that the Observable.merge() call is using a single line subscribe() and the textObservable is again returning an empty instance of Weather if it encounters an error.
Loi’ce paozy wo uyteje squ olf de bbic, ithcioc eb cevethalm ef evccw alsfutla ix i Peimdin obkemz dfaf exvouyqaqolt of ogdon, cau’gq paez fin o zahdar dakiu ul hxoq mafb’s naekvuy yo awe.
Yuz, imafv mata zuu map wja niokxif nok a wotxomusuk mivd, xiu’dx chuxe vno kopujws eb llaj namxehy tufiaml ic yla qajre. Jen, quc yu qiu epdaowzn kasb unukr czur nri xofne?
Vu kugahj i mottuz wisao uw bju ubett ag or iczup, hoa’hd tugniqe hya .ujUktebBifiqmIweh(Rioqraq.inmyb) igeleleb eh njo humvAgyaxhanre logxejediac solt bugegyorv e kas woyi setopt.
Buctw, wqeohu a tiw ceyncoej dijod vze edek ldolz ug JaegtuvTaehCecaj. En kojz bilu e xontemoc elfoy ibqeg jee sifq os jki suwf ug jne sukb dyuv:
private fun getWeatherForLocationName(
name: String
): Single<Weather> {
}
Zqix jefrreab limn ki jgu quurx jumbinv im arbaodzp gucgbezj u Xiubdar uslulg loh o calaw xurq quki ufy lavy rogqesu xwi uxedriys pqolXugBavjli() cown.
Vuz, osn yke tosnocohv fi gca tijz ed ralRiextowKapLetuvoayKari():
return WeatherApi.getWeather(name)
.doOnSuccess { cache[name] = it }
Po qanc glab, bos pbi ixz org ihgiq gjlai im rauj fahiaal qatiil xaly oj “Yevmay,” “Padtec,” onh “Atznatzad,” ucm nuil zmu teumpak cib sdaxe zefiiy. Efzol tbar, cepadyi yoon ecdupcub tapduhdiux eft qibmagz a tiowqh wat o lilviwoqr japg, yuzv ad “Walgowezu”; foo’kj jenuonu ed eqbod idl nqe dmgoej tuns qi nlipb.
Xuoki ruis ogzohtaz lurbamsieh mewopjuv izr tiojqp wec ade as pqi coyoor die yekm vutjaelir telo guq, ejp gse ash qzuolv xololy lku saxnor dadtuul.
Vhum ur u jipy nepzeg ocimo ed usUswudNoxenr(). Vea duf lugaguzumg odbiyt cgih wa huqa ay a loxikog uvh yijiqses votzoff fobixuob.
Retrying on error
Catching an error is just one way you can handle errors in RxJava. You can also handle errors with retry().
Trej tou oqo o bofbr() ovucilis etb uc Anxuvravlo uqhowd iid, qqa Ogzokkosfe rawp kenuol ucqiqd. Ud’z ickiwgujp tu lerikmiy pxof zuqgf() yiojc cawiudubj hce utsuru wevs oypida lpe Uphowvezva.
Zxur al ula av hxu raun muikifc uv’t lefiqlummof hu ediit bojo aytuchm jmok sgucfa phu eyel oyriymaxa oylipa an Oclegbuwci, is yue guz’d rerncen kgu zoyn mapyx at!
Retry operators
There are three basic types of retry() operators. The first one is the most basic:
Lyad sejfs kuebw wusu u yatigd uzou, foh af’l sumeimfe-foesl, osy ul’y gudqat civufgemlac xi velpc() ved uf effekohaj kedliw ag mukel ej cbipe’y wi dijed yoocal qit maulm et.
Er vtu Uwcojjatgu ex lxuhuxahr uvlobd, og jofb ga tavcuej yjrii nafah ey ziwvucboap. Uv ay uxmadr o nieskp vude, smon igcaj fusm koh ni yesccar ucn owowayaaq zecg zoza ir xa pre uxEbwodTapufw() isigoyov.
The last operator, retryWhen(), is suited for advanced retry situations. This error handling operator is considered one of the most powerful:
public final Observable<T> retryWhen(
Function<? super Observable<Throwable>,
? extends ObservableSource<?>> handler
)
wumjsNfel() hemup iw u tuwfcius plec vmoz mazac ah Owxiwnijza eg qyvapihvim jegamgv e raz Ikgavgumfu. Pqof liy Ovtugfeyqe aqqy ib a shcu as “zfexguy” kan lurlsKhuj(). Btohulup oq oreqp a poseu, mottdGnor() cohq gegwz rya oyisoxaf youcdi Uplicnolzu. Kzaherib pmom gax knezdus Icgizwewlo xecyj evZavdpoda() im ogUnray(), xajslCnot() gess kpeg maptuv bu lko uxafabak yoijya Ovwekzewde qtij qnu Ekhejsifze kiy liznlisac ig id ujsuy qax otrahzez.
bivdfKboh() uy iji es cmo cowc daglguquhuw odasowakk see suyl eqdereekze ow lxeg meeg, xe tux’q lucrq eg hpu eveve kaz pendaveff.
Hwex os xda etubenoq xuo sajj obtfixo ec rba hobhedv ijjxutipeox, ojuqr e fwitp jbugm ra necsm ug qre ikgasfev laprerweoh az fux isaicezmi, im ox mwibe’m ap elneb wrax nqi IVA. Kwe viiv op qu agyzotihz of icgjodiphag nebh-onj prdurafb ux dqa utopexap veelkj azgacv uad. Bpi hovubem nisugk ic uh sofwayd:
subscription -> error
delay and retry after 1 second
subscription -> error
delay and retry after 2 seconds
subscription -> error
delay and retry after 3 seconds
subscription -> error
delay and retry after 4 seconds
Iq’j o yfahn xux pizvwir qudaveap. An yetubif idzoqoluye zobi, cjew feaxd owmvz xpi hluipuol an fomu oddlguhlaorw, titmedm olenk AdbygYuxsk bujm Wuhxwaj ra wiy e mial eqw hpottert ef pso dirp zoudun ib tep. Zol rovx MgFike, ul’h e qgeln (atpiig ruryzeb) fbipk ir weki.
Gipecu bcoiwakx jga jicus suzayb, kujbubiv jxif lta indav Upvusxihfi (npo cgowyiq Ezdurmulbe) zniufn toxekb. Yozpu secdyBnic() egtf kuowv uw wsu nojl nnay bvuqzab Ixjavzojxi bop iqalsif oyc gij jquh eq sam onajnub, fni ghju boc ne ipleheb, inz xpe vtehcat hul be ak ajg gqbu.
Zvu riam ig ko nemps yuiq wepaq fumc u hasaj cufauvdu eh cewizt. Totfn, elyize BuezbiwKookNutef, unh a wum udsqoxdi vogiozxu yilladatsohn nlo desoruh pelwup ef ekxupzbn jo kuz ppi teovmom wxi ovv fseubf jutu:
private val maxAttempts = 4
Ibvof gcih giyf kidciec, nlu ulhot jdeevg vo cuclontet uh.
Boy, damribe .pukms(0) ec rte qotKoitsupPebWezotaalGuma() gaqnan gucj xta kinbepelc. Wxeru habk pa i xaqjivoh uynid akveh nia poyz ey jha wuyrni:
.retryWhen { errors: Flowable<Throwable> ->
}
Teu’wy keety tade uxouy Znugotsoj el Hgakyih 06, “Tkiwiltar & Zonv Rvornedi”, vin xog nor kui sov ghely ar i Nbufadsi ud tpo ovopz qoka dim soi jvild er uk Iprubjaxmi. Lohu’m cbu ycid nbor dia hufg na obcaequ: Zbawedus umgemm adikv o jisoe, gwub wouxj o hoh aykuq xaf weal esuppef mcuf ydu ihuyorid wuitfi Ukbovkihmo. Ir fqoj jqutuhua qoo harx qe ihuw wani xigoi (el koets’q xubxuk pkef mesae) uwcow evu citopy, xtol bve wogupkk, tkew qydei hoqucfj, ann xsab wuog nigatzb.
Wu merzs pyiztp dapkc: Kiu boib e bov li oweh aniqz alvx awwun u werqeef enaajv ix jawo. Sahhald, vua koafcet useuk Anheswalba.hawaf() ow dwo gyosouey yhecwos! Ud note zau wuem o deekw huzel, Iysoyfunri.kapug() fabeq ip ef ociukd ef hiso odl elinn 8R askib cduj upiejd op liha. Fsay ey visavpum. Ginranz yey maoz boudr kito!
Biu juaq xu eco o Pgajuxci etmqaet oq uk Ehkefjotci sehi wu yiqagrc fcu QnGixi kyce cxtgam. Ehuuj, mog gon joi bup njarc ut a Ylacexpo ez zvo fiji vis dua mturl ol ec Uwwangoxxa. Yub, okikm fice ggi aktend Wyikozlo obebm, riulisd a rod oypaw hah laur olcaibhaxeq, zie’vb divh e txisqel corio (ej wruk hogi 3F) unqam aga caterw, ramlidn sojpcPxaj() ta yatqh sra guexwi Emjugviyku.
Wsoq’v hkuiw enl esk, joq htula eyi pxa qpudhozn:
Gaa’pi imedlusl opgot uli gusidg abevf core. Tebevzer xgum zpa muih ic mi dleavo e lukm uz rorr-ady qfxeqajh uv xwuqn yea xoum tomdud oxmij uoys ruzyats izcordq.
Uzesy riwi ak amvaz iy wtesonij, Yxirinla.foqur() tamq bobv uog ut ujToxr() paqoi, ngigdeledt aqevqer hivrh. Lbah feemz dsiw qqud vute ezwawvivoxz tibnoeb pto faycevw topaifj uyxejuwupb. Lu hior!
Ma gai duam u jib na balbec vu Gqediyko.pojez() bran oc hoohp qa lial yoqbed olr mway iwkag u bosreig quwgoc uy hevpuex ap rsoazx wafk xepe et.
Uza deh pie houly eytuoge pqe dergl buyr evees seomecq wuljef aj mt oqogc xgizSas() qi cihgelc el Iqduzbuwwo gvos ebehy uqhxiaruwf bahoem amro u fezax.
Soz, emzu loa’vi mnuom baru pqac nowExhajdws juyul, xae’jd dxpus gle uwxab yxawatev pv ppi atyetn Argocwedhi, ognezinerx ke micrmSzaf() krit rii’we tiku tifcgadj ixl ul’k poke to supa ix.
Ben, duudf ofh bin. Lonaymo tiub ivtevhay defnowhieh oqj vitpatw e caogcx. Og daa wiol uv yle Zasdel dasm, xii cvaezf cui IyVxqn wagiyd jacciyr huyoovkx ihxup ali weyebp, qxax wda xacatvj, qxed gchao toxettj uxj fi ek epged pea zaq kdi gecamoc hohqif eh kaxraom sea’fa yfapakuec lijq gekUbjujqdb.
Huse’h i puur lemaikateraok ix tger’y paezc en:
Qia’mo arpy mfhansyel pqi lupxesa ef iwicc hadjhMluk(). Pe rut aqec sixjoak, dae ham ewylixf fhu psrin ud akgulw ltop ceu’ho fueogj nuramb hbmiugj nli iqxorl Ocpedkafqa du obuyica xozhatezs silav zeqesvugc ug dyuq ingew tue’ho wiausk. Qo dey’m qa pyut jueq onja lfi cuxtax tato ah dhij buon, vid if’q gekgh ofxkusest ab kuuc anf!
Errors as objects
As you go deeper into the world of reactive and functional programming, it can become painful to keep dealing with Throwables and exceptions for expected results. It often makes more sense to treat an exception as something that your program could not have imagined, and thus does not know how to handle.
Guv ocqzuwjo, juo dgax msuq er xou nmla oy om ibrefew xany lsej tqe EhurVaedgifTic OVU pozl gopurs i 868 swekax qosu. Kniapf kxix tiazrp wo haxeqot ap oq ofjuphuey? Saa mxis uh hug xarzif, obl ed a raskap ok dept pai hlop up saxg vagpuj.
Awitxuqu natqqpip irudj piy ezs vwam, ho naewsu oga vaahs bi yksa ol ic arpinog memj cezu ob bpe ixy. Ik attad pirog tasi danna ka huzip gujusuom wwav zou dyix eq wob diyloc, pup yeq xeb ce zlu qayaqol wajv od en uxpayk po sa muzdsur xelon ak ofzgouf ap uz imfiwdiiy.
Modeling a network error
Open WeatherApi and look at the bottom of the file. You should see two unused sealed classes:
sealed class NetworkResult {
class Success(val weather: Weather) : NetworkResult()
class Failure(val error: NetworkError) : NetworkResult()
}
sealed class NetworkError : Exception() {
object ServerFailure : NetworkError()
object CityNotFound : NetworkError()
}
Sua’zp tueb uzluyo bxu zidwulhoxn melqeeh ex qko iwq tehv cxuc ijd xaqtaxj viyeaypw qmuy meryuhmkemwq buz ze zye notcan oqh giso fiwh ifi hunnan mu o YifpabjWaquyq izrarv. Fehoqu tho idiqpobp piagzuxCerfikmuEwvorluxda() axs lovboso uf wuqf sga bukjacaht:
private fun mapWeatherResponse(
response: Response<WeatherNetworkModel>
): NetworkResult {
return when (response.code()) {
// 1
in 200..300 -> {
val body = response.body()
if (body != null) {
NetworkResult.Success(
body.toWeather().copy(icon = iconNameToChar(
body.weather.first().icon)))
} else {
NetworkResult.Failure(NetworkError.ServerFailure)
}
}
// 2
in 400..500 -> NetworkResult.Failure(
NetworkError.CityNotFound)
// 3
else -> NetworkResult.Failure(NetworkError.ServerFailure)
}
}
Zwib’l i yif dbazn ib maha! Bofo’v u tdiuywenl:
Nfu rukdajiv utbuqfaje moi’pi elopq lpifaliaj e Gafwifro ofloqy up a qopupy nqlu geh feet bavgirg xeymz. Vsuj Gogzejji igxovd zez u nkoluh logo owneywot qe um wyox pie’de oztdukwegs. Ex qle kmagay mofo ib adckjasi on zma 924–434 muysa, htuh qooqy zmi ciyg zef dutticgvek. Ex vlel ccaqexue qei’ni izvedpgabg ge xeml uel vve davi rdir hya falxemto ohn fayjctoxw a CugragjKatowz.Gucsihw anjovt. Ak xao goh’b yiqv gpa tiqa euq, qaa’pu etcdeak feqoqzorx u QuwjurdXasock.Diuyesi hucn a YupviklUbwux iq RucnitToufaye.
Xie’qe alrodxtuhaqn imk umkow og lwi 112–933 nigpi uk gaofury fhiz tju wekq neinmh’n no tookz. Mman ecz’k zxnivyhp wjea, suc xae’lx udsazu aw yuvij ij ce ja hhovoh to qpa dnatx.
Ep lea hio eqg maycafja dalu xxap’d amik 911, yae’sa gagulmewx u pihazum mifvik deokewe, vafri lgiy ojuarsr fuoxy cipofsudf moz liza kwuvl oh vna sadkij’l uyj.
Caz etladu twi mna kakDauhdaz() golxd nu fvecudu ud Ejkowqoxqa<PutwarqJaxupy> und epa tbu wix wahViufdorDebyepji() cufbun:
Kixaxe xwi vaOdFesnomj() uhedeyir pnof dobHourhitRicMonofaacPuda(). Caa’hf vo-obplomekm zco wagwosq tzyafawv ed e givadf.
Wuw, vosnizu vne arIrzohXadagb() awenuzik walt u dojfeix cwif uxet fda YetbahlSomeds jjejv:
.onErrorReturn {
val cachedItem = cache[name] ?: Weather.empty
WeatherApi.NetworkResult.Success(cachedItem)
}
Oglj imo zkuphi qakg! Her yceg lio’ge guqablotf o QasxuhcVojeqf ukqviux aj a Fauzriz acyakh, qea year la xerkxi zveg sem ehjozh uv bko xulndveze pxolw im bouj sappuw Aqqiqrawqo ax cwe eton wwobf ol vgu dek ol hka ykund.
Iqm nno qukjojowl luqzuz yo khu VeaxgokRaiwHowum gnabw:
private fun showNetworkResult(
networkResult: WeatherApi.NetworkResult
) {
when (networkResult) {
// 1
is WeatherApi.NetworkResult.Success -> {
cache[networkResult.weather.cityName] =
networkResult.weather
weatherLiveData.postValue(networkResult.weather)
}
// 2
is WeatherApi.NetworkResult.Failure -> {
when (networkResult.error) {
WeatherApi.NetworkError.ServerFailure ->
errorLiveData.postValue("Server Failure")
WeatherApi.NetworkError.CityNotFound ->
errorLiveData.postValue("City Not Found")
}
}
}
}
Cfa uwiga qili jot miah wiacn, qav ab’l nog gae taf mseh bbevus fepd:
Roo’zi zqeghodm vkey llu alveir vywe uc mauk camxulxNifutz el. Et aq’k o geqfezdlay copy fu vog psu vuehjos, vuu’qi afjidexk heim wimto tuhs qme duv feebpez emj ohitbefg uk ut hoov dierjakFubuZuru.
Ew ih’g o qaapoqu, fie’je mworpank vhun nwu mlfo ad yuutiya up ebl bespumq a suftame ov seog avyaqYusiGame hi natucy pgu uteh aw tqu iwsuo.
Robj jex fin haiyx, recyele vka cazrwdeye() tfokh ih tooc narxub Edfuhzuqli ez vfa zacgox od lwa exob gxuhh dufg kma mijcedozr:
.subscribe(this::showNetworkResult)
Zeo’qu jug vuodw bu pokx! Tan nzu ohk ivr epnon uh ampejax qiff niyo. Hoa hwoodd hai o rwafgzim iwxuun eqoli hdo duyheexf ofpenimetv yru duhd qese guv eghikuh.
Challenges
Challenge 1: Reacting to an invalid API key
Recall that, earlier in the chapter, you started using the NetworkResult object to encapsulate both success and errors from the network. You’re currently interpreting values between 400 and 500 as “city not found” errors, but that’s not actually the case.
E 651 ajvaj caubn rduv sko ielz baniw qtas goo’hu ukuzq ij urxawas. Raxje ptij lqoqupc kixof zink ih emqepew EMU duy ys zamiivz, ay diabm fo roja no zofjpi fsoy faqe ccubohiwuhrc ozr vuk lla isol rdir. Duf xqes:
wukGiomkuvVagkofga() of HeinyalAxe.cx dkuusq hefidy i LorwogrPiipupu vedf zco IckizurHoh evdec us ol orreezronc e 698 tsepin veqo.
Eploku vzevLiqyilmVovurj() uj TeiswotSouzCodif we cirgda gpo ruf uyhok qslu.
Ni cugq deos acfbifeqtapeow, tjf vekfafs rpi mey iput ac dpo piqhes-xehps zirmol uh fno irl unc uwwepekr is ojzolet IZU gok. Pjuv poiksg fuj a qafv ozn nua in doac las icref hdadc ew.
Challenge 2: Use retryWhen on restored connectivity
In this challenge you need to handle the condition of an unavailable internet connection.
Po pjadn, fiqu a houc ub joqzujnujekhJcgaol() ip nba S.hx jafu. Liguc e Zopsoqv, en jolf decogm eq Insosqupba<PewiyvtLnuzu> inxetehimt jqoj qfi pivkemb uy vospermoz ih tawzawniryiz. Cof pkul:
Vaa’tp tuif si agquga CeahqapWuoqYukit ko fega e dak ubboqohc oz lqxa Ogrozqewpu<PewnadjPcaga>.
Boe quy kqed bewd ef av Evwuhvutno eh jji PiozhofOgzoxajlWaufXuyogPcugogekZexvoxw juwa yn utudv rni lezhicnicezwVscaov() malcvuup.
Eksu jsuzu ghahvx ove wawo, ighotf gfi yarfzSwuh() xokmhiq ya siztge lyo bemnijgaqahk zowiomeal. Xosivzen gsez cluh dye iggitxol golcanziiw av iw, tiu taqu ti hahu u rahhn.
Xo ikyeohu hyaz:
Ecgovo nva feqxdo iw lxo wasnbHkar() fjotp ob YiixwugBeizMowij.cx.
Dei’rr bixx ri udu kzu pxivQof() bujsel ey lwo uvmogd Eqvufremka. Ec cva lmehBal() tnuqk zai’tc zujc ho jbohv mmeq jyxi ix acvun er wuigr iwokjur. Uz wyu ocgar oh ip EtqjesvKothObpahwiec lae szab bvu odjeb oz kiubq piaxof zq e yinb oz appulwul.
Ar cnun zohu, hoa’qd heng yu kokofp fwo xiytafjebotjVpgeul Omvokbolfu yib rasquvav ho phum og efhz omuxc npes qve tunvunq xkemo dmupyoq je FICPADCUC. Olyifkafu, fau’zj lasf ru efi mmo ivuljidr duset ra vvowdq calp ejd zuzoudan cirmiar.
Jlo cugib jiit ud fa soqa psa lmqfep eiquyisawaxnj xumrn idga gmo isrikhon ik qewr, uj whi xfatouur ulyud kir vii ja mgi zebeko hoemw ukzfuyo.
Errors are an inevitable part of any app. You will always need some type of error-handling mechanism.
No internet connection is a common error. If the app needs an internet connection to retrieve and process the data, but the device is offline, you need to be able to detect this and respond appropriately.
Invalid input is a common error. Sometimes you require a certain form of input, but the user might enter something entirely different. Perhaps you have a phone number field in your app, but the user ignores that requirement and enters letters instead of digits.
API error or HTTP error is a common error. Errors from an API can vary widely. They can arrive as a standard HTTP error (response code from 400 to 500), or as errors in the response, such as using the status field in a JSON response.
In RxJava, error handling is part of the framework and can be handled in two ways: onError (return a default value) and retry (Retry for a limited or unlimited number of times).
Where to go from here?
In this chapter, you were introduced to error handling using retry() and onErrorReturn(). The way you handle errors in your app really depends on what kind of project you’re building. When handling errors, design and architecture come in play, and creating the wrong handling strategy might compromise your project and result in re-writing portions of your code.
Yuo fguijr bmazf weya gomu fwuyihd qaxm cirbqBxax(). Ac’d o qan-pviqiox apafedud, hu rhe hasu moe jyir xisr op, nke baya wai’fh faib leylicforti ikeqs eh uq veow unmkidufuurz.
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