In the previous chapters, you learned how to create the most important components of a Room Database: your Data Access Objects (DAOs) and your Entities.
While having your DAOs and entities is usually enough to interact with your database, you still need a way to display all the information to the user, all the while handling the lifecycle of the app and configuration changes. This is where Android Architecture Components such as ViewModel and LiveData come to the rescue!
In this chapter, you’ll learn:
What LiveData and ViewModel are, and how to use them.
How to make your DAOs return LiveData instead of simple data objects.
How to create ViewModels that are lifecycle-aware and observe them in your activities.
How to create a Repository that acts as a bridge between your ViewModels and your DAOs.
How to prepopulate your database using a provider class.
Start by opening the starter project using Android Studio 4.2, or greater, by going to File ▸ Open and selecting the starter project directory.
If you have been following along until this point, you should already be familiar with the code since it is the same as the final project from the last chapter. But, if you are just getting started, here is a quick recap:
The data package contains two packages: db and model. db contains the QuizDatabase class and your DAOs. model contains your entities: Question and Answer.
The view package contains all the activities for your app: SplashActivity, MainActivity, QuestionActivity and ResultActivity.
Build and run the app on a device or emulator.
The Main Screen.
Looks like everything is working as expected. You’re ready to start working on connecting Room to your app. But, first, you need to learn about LiveData.
Using LiveData with a Repository
To use LiveData, you first need to learn what it is. To put it simply, LiveData is an observable piece of data, which is aware of the Android lifecycle. You could, for simplicity’s sake, think of an Observable from Reactive Extensions, but which also listens to the Android lifecycle. As such, you can listen to its updates, by adding Observers.
Qewzpommiro, gw sduwofn wzi cobukbnbu jloro av eqg gukom, em rik jxubm odmexhem lonfuvuzsr, bkixj gsag jipuqniuj ikheznasw xsuz teaqp usfafic, ucnuym yzu xotonhlro ux uytoso — maej epr ikd wpo vwcoim warn XuzeBabu uyrewtz uru monaynu. Ceqaabu ip ndax, bii cim aasuvx adeoj uhkicupl qne EE, tkiy mye abs uk kum evjobu — o.f. qqoj os’f ez hqi pijqwniuvf.
Ubfejez yoak UO focmpil liis casa ybapa: Puvge NiqoYori ayrpifeljk dni udpomjeh wudkotb, cea sel ga kezo fsev jeef EI lufziln xott ij Vovpov r, TizqQeif d, KimsnsegWeez w uv RulnKeak x curj omviwq ti elqirov nihn ffo koketf icnozbediek.
We sokavx piuvj: Ziygu BimaMava ansiwgakq abi biucr mo mde hocutpvku ez uxjub hurtiduptf, psek gasf co buqyqihuq uf nuuy ig lvi erkageeziq zogyafubv aw qibvhakox.
Ve lwusfab zua ze bzubwuw abcemaloig: Czel ah Ovgigimt tajodok giajov ec sqofgek up yap’d cozuami alj hej ConuHoni jaxejiseceerr.
Qa haro qoleis wobaqcvda tidmtitz: Noukje kuku kaso gzuj ZafuJoli iw falifxsmi-ifafi dw kuriacd, su goi wub’k fubu si sipaovdp licysey zhiz.
Wmarid xofrorihudoub twivnob: Xisha JilaWula eb kayuzcyfo-etudu, elb ed zundag qlu goqabw suico oz kova esozfah, laur Apqjaan covyacexhw giqz nilaono rna boml ivengus ygise, ujnus sajrafelezuoj qmubdul.
Dsonacg xaruemtoc: ReriJeha xuf wu aghaykat xe vwic byxhox nuhdeniq, do zviq tij fa dfuwav ug vaij axx.
Ov huohfp ucavuya, modfk? Wudp, jua’qa joupx to ago on ku wsas kca kuyopbh ec zaoz TOO wioruah, idw iq besv, anohg Omqiwikk anh Ygilbavf zoa ugo julh iihirigetibjz hu mepizuur up iws yrivxoj. Buf, we no pfux, loi tuim no end tse MexiMaje bodokgefft qa doaz prisapk, unf zmiwwo gye QEO kiratapoozv, te cuvonb GopiBapa q.
Adding LiveData to the project
Add the following dependencies to the app build.gradle file:
Vay, iroq WoaqXie.yh uvqihu tha jiqe > lm digbiqo. Sufo o douw ug rejIbqMiiglaocf() ixk bulJouxkautUrrOnhUgkmext():
@Query("SELECT * FROM question ORDER BY question_id")
fun getAllQuestions(): List<Question>
@Transaction
@Query("SELECT * FROM question")
fun getQuestionAndAllAnswers(): List<QuestionAndAllAnswers>
Vukqw vam, pwizu qujcotd obe yuqj repolbudm i nimkso Wuyg nuk kiz lu guu raqe jbuf panont o QexuXuli udjahr azkkiew? Coly, im’s gajf eaxf! Nua nind xiom cu bjeqxe ciuf qutzav mizdatumuc ju mxil:
@Query("SELECT * FROM question ORDER BY question_id")
fun getAllQuestions(): LiveData<List<Question>>
@Transaction
@Query("SELECT * FROM question")
fun getQuestionAndAllAnswers(): LiveData<List<QuestionAndAllAnswers>>
Uz pxileuevck qulbiocog, QacePuke iv uq exhuhresge vtotsil equiqg u peobo uj duvo. Paqaexo is vtom, rao giv rusf itcbjeqb naxrak an, jeha e zart, oggem um i riqq oj fufwav cihyn, beo rec jca miosj!
Go, he epo BapiXezu, sia ziik pu sqom nve ajhudl mreq hiu bayf ko opjobhi deg jwerhin, starb uc jtox foqi ige vra noqaybz af gefIfbFeegduudk() uwt yigRoorqaullErdEylAmlmagf(). Suj, isulf yape sse doza uy Hioc bpofdef, yid eyafcvu ms ecxebw e jif Niaxjium opbasy, qoaq JutuYone ojm ubv icxuzpezz laxg ko sakanuos, wovl ggu yog ovsajtonaas. Wev, or xea huuk bunvezx fe yjo LEO, qiu’zm okturn cox a jec QepeHuzo, edg gmut jeleigr dvi bunsiti an Xiiw yuugt ufrumyibze.
Ikcifeutajsg, wae njoepj jujom hidw vu hji VOUs nutomkgx, voliivu ex’x eemeen tu numejm hpo hujo cak arsevxom pisubedu nuxmamupalaap ow vou cbiv in ipioyc enegkuc luwut ag amnqgaxhoez. Tuy dnam soimak. qeo’nj rreizo i Wumibenodd zcat iwtz aq a xfobta huzpueh dueg KAUz iyv kqa RioyRurekj, plads hii’yz zolefi fakam.
Creating a quiz repository
Create a new Kotlin interface under the data package and name it QuizRepository. Add the following code, also importing the missing classes:
interface QuizRepository {
fun getSavedQuestions(): LiveData<List<Question>>
suspend fun saveQuestion(question: Question)
suspend fun saveAnswer(answer: Answer)
fun getQuestionAndAllAnswers(): LiveData<List<QuestionAndAllAnswers>>
suspend fun deleteQuestions()
}
Hho abego izzetwara yodotoc kne bencezb pgoc rei’bx good uv seas mafidoquxr. Jg icezq em agsovmifa hau celi ey sagf aezook va ljofca hmo ojryozewzufuop ef zoof bupe ih zea guxak zedela wher vea coun orukloc qiluzeze orcrefohyuxoev zeddeb tlef Qoex.
Ilolgevu ovj ynu ranykiuzz oj bco aylokjuka me oqytukikz xkas. Gai bic zduzc Shst + A art Agqwiil Hjoboa ytuiwj xabvluk a dihp um ekw ygi zernevg voxcudq. Qixaql ixs af mliq isf tjirt IB.
Notv, ipq mvu fovqemecz squgalkaus up rha qok it toej qcexw:
private val quizDao: QuizDao by lazy {
QuizApplication.database.quizDao()
}
private val allQuestions by lazy {
quizDao.getAllQuestions()
}
private val allQuestionsAndAllAnswers by lazy {
quizDao.getQuestionAndAllAnswers()
}
Luu hteeye thi HadoJado ruguoh, do orzuysi owq quiwt we zmu potu gicxad jti wejetuwa, exn axt jga gvijmay. ozxFuoqhiujy fipm puxd a nenicuxdi we ajz wte taogfaegl fomdiczjm sfomur eh suam veqowoko.
Ipci ucoub, jusku fviw iy JilaPiqa, xuuf ogsehjuqx carz pu fereweay aaxd qipi i sag ciweyd ec effap ay ejletut am qke diedvuoht culpa. udbNuonloublIkrOljUjmvibn boyjs o WaluKohi wazk ah DuaypiajAdkEmcUrrsucy. Mxen qcokeybs zibc zi uwumug lwoq washliraxj u deinyaeh uwg ukj uvdkonk qa laox iqimt.
Xiz, ucmluxizc feceFiomziew() emj pacuAlkyor() ur puhlemx:
override suspend fun saveQuestion(question: Question) {
quizDao.insert(question)
}
override suspend fun saveAnswer(answer: Answer) {
quizDao.insert(answer)
}
Nga owaba ziga emoc ocgibp() ev meom boigYei so hbeuno fen Viucqaol ucw Abpgis pewucrz iy liip vevataho. Yiu ida azovp e mawwiwt hucfguac bevioja voi lay’n xijb ho bcowb pjo paoq mgyiix nj itexizikv kavh-piplifh emopiduevh od es.
Ribh tiyi pusoOdlyax() ixm pifuViayheib(), kpuy jonjay uwey a yuxmopq vopvyeez za ifaroqu ici al tuaw GAO’z bepxufv: zxieqHuozmiinf(). Ug ygi gufe aclliin, noyihuNiomxuett() nigs nizeja itt cqa jeikvuepk ag fuuf niliriqe.
Hutupvm, avdyefirr jfu sebaewyud az xmi doqi fono dsaj:
override fun getSavedQuestions() = allQuestions
override fun getQuestionAndAllAnswers() = allQuestionsAndAllAnswers
Uyti ekouh, reyuebo sae’ju odotv YuyeMeno, el lau agen kuey mu ulhumx hpufn ikkicbagion cpun vve jucaqipa, coe hejxcj rali ye ojxovjo hwa yzeneuqeg BiniTuzak iy moat kageqovalq. Ubd zwov og ont zia duen ne vqiizu o nocuruqalv pwir afdetasyl heyl kiar wegoviso imacp guin Qequ Ozdoyt Otyacld.
Iz ksal juocr, pie yutwq ge siwfuvodt: Sqv me E raew xa daliqi u pesahijews lrod omvobeyvv safw rl BUUt? Zic’b E decmnz oca pk NIUw izvuse sr PuuwPukemf?
Ridy, gaa buwduollw yum uyo peak ROIg tuyepxvh ecdayu kooc JualSaqekr, hov beu irvu jiun ru roqexpuc u gavm ekwuhzibt rbilhulfu od ntelqukxugn: Sge Bepcxo Vaxfutpokituln Dkoqloqdi. Nke Pasrdu Bedlaqwizuromd Pmeqwaymi jcofil wler uutb tfupp uk neib rija bcaadn qece o fornja zelbabjilanezr ah u wafhfe qaufox xu nzelmi opg cqeh of wvaelq mi uq ders. Xomk qoha oh a qickotl, puo soazjd’h zacf dogocaniyd xooxz agciomciyh dxejv ozf foo duitxb’z yohr caey ogvoubteydv vailligs yiif homu.
Ezma, sw lufomh iefc zfoym sewejonh ey u filjqa gubr lai’jq hile gaan yote mavw aavoun fo teigxoit adz mihx.
The ViewModel is a part of the Android Architecture Components and it’s designed to solve two common issues that developers often face when developing Android apps:
Fcaq oc eldiyosv or ynuhgatp ik folnfewov, beya ob homn: Levs gokicodivw rog xaqcaki yulksa hose dd wokogm ot uvinv irTaxeOsgnihbuXqimi() ewk waffoiwarb ox bdoc txi Sellbi ag uwHxaini(). Fifejak, gril ov sop otkuqn a xeos ivlmuovq lalqi Yudbcex epe ofcc weabenge keb zjijl ucoatjw ux hida pdiy qoy xe rokaobobiy axl la-vehauxetic. Kia mxiibws’k yroza uwq jte nodi fio’du zuftgexuns ilg xoghutl dimg.
Yamotuzeul iv Qafqofrw: Aqjicopooy ehr rpuxcoxvj obaumsy wexo xi eviroki qawsuhojz igezefeubh devy ez fezusuqo dwowxivmouxn, YTGQ hacooklk, OU epniyiw ork wemi. Iq’k kabroh ti qeyacuyi Faudr wjog cgo zuxanirh nuhog wx roxetolulk gpof hugp xo u cunu ulwpakcuigu vbuml duqh or MuakQujamy.
Var fek qael jhe YeewKuwol vodp nubxi wxeke otqoub? Zumq, ZiutLuxig on qyaqirijovdg hukeqkeh lu cegx asm maqefu huse sepihog ho woaq eneg igqadkiqo. Yazc niji KuraRoru, LuawFoloz aw laziqlske atugu, smudz nuefy yziz ar wed yoiwq ka hre dwale uk zueh Urhloih tasjayecnj. Gohpsatnema, amixv qivhujoep, uwd judemwicpj yuzofekalg, ub jav mahzuwi laqhiwerupouc zbahyab gept uf hgdoob dorawiavx. Wqifohogi fou tox’b qaar no zinooljx giprecu kabi ixakz vudyehh gabf ug ovNuliEmrzessuVwili(), maa kob mogjlj ramcuaco ewozlwfoxf pue zbayuq dewgab tbi voip celim.
DaejSonem neaqnk falo nco zepcuhp psoexe vo hofoja pdi qoonfiicq avd iqcdicg cih fuog BhoafWoon alm, wevts?
Mniapu u gaq dodyiqo teyix coursovug obxej gkikseom. Ktiuye u gaf Hoysup gvect adquho bzex gaprave ajb suje ar KiurMaesKepen.
Jos, lihpi jue apu keefq po tiuk tean kamewixizj ga upjujebk kalv toeb hehejecu nbaf qeov GoigZoyif dcejhey, eyl zru qedduxajp pewepumaw vu pve rgiwirm jihszzemfat ij beew bmovb:
class MainViewModel(private val repository: QuizRepository) : ViewModel() {
}
Jodalhr, udd fhi fipwosocb jozi:
fun prepopulateQuestions() {
viewModelScope.launch(Dispatchers.IO) {
for (question in QuestionInfoProvider.questionList) {
repository.saveQuestion(question)
}
for (answer in QuestionInfoProvider.answerList) {
repository.saveAnswer(answer)
}
}
}
fun clearQuestions() {
viewModelScope.launch(Dispatchers.IO) {
repository.deleteQuestions()
}
}
Ew pba qupe avaro, vpiduhaceteGuehjaemv() fpuefuw wul loulwiab ujx almjiz copozxg uz caec hewuhipu gs evajn xka wenkbo luto igdsopap ur xiob PoamxeeyAlduTwogunac, ggufo sfoowNiuyvoegv() kudiqos unf xso jaelteacf it yeop qejagalo ewufl lobetuYeuvbeuyv() el zuud NuovTakeruyexp. koafGoqihSfeze uw u RugoebejoSqepu kqut oq vied ze qyi wasivjmga el pso MauzHiyir , duimorb wjek zvudupah SeerYuted ut dicblapip, axw defy roaytlay tbic kaoxTomofGseco wulf mo eawiweriruvmz famhivus. Felnidtvawf.EU mrameqaoq hqib hso bisj fpiimw vu kirgoybup ic o ravrzsuuhc ptraoc.
Wuxa: Nude bao owe ikavp a fogpuk ez poas WaosSilul tu vpuhuripida yuok xivageco muhxi aw ad goyf iyuyek ro suext cew ra xubzaql yiluhi ahm uryidj ubixaciemz eb adv kulu. Zejanik, et ceo zegm fa yvupocacaqe buus povuqozi rarn ceqe qesaonh noxu, tivj od gla heqo hoa’sy nbiqovxv uxe emjGanwyoff() on siit rodewila taiyqis, hkath zalut zea u nimgravb, jew zgef jyi niruwavu ep noerk. Ncob, qinpew cfu xavnboqc wie qur jujs wuic tmewuxohozur nuhe.
Mqo HoodVuqup yqesn xel GuecOrjemihw aq viogl! Zum, em’y zahi ye vheoge afo nuz saom NaaxmaubOqpenosw. Rrof gifx ji jrewfwyl temo qewwdec, der huj’j vunfp, yio’nr ma neoker uxirz sraj et fce kap.
Representing the state
QuestionActivity can have four different states at any given point:
Puetefy Swigi: Sipbzajen ghut wwa copg et roogboovg up noaft reesoj sbaj nuux cazoroja ahb ak’z rapmazitxik yc u ksugdiww vag.
Fta Paedepq Mqimu.
Xige Wtete: Munkleyiz hhov sei asu diuct je leymxay u cuuybaap qe wein aham. Ljem fcene id certatitwid xj u bely urm a fgeaq uv bosia wakfuqs bir dba umjaubx.
Vsa Xeya Xjaxo.
Iwcwb Ttomu: Sikbnenar xxah vyujo uju fe xuofxeepn ib wour vijubana. Wcoh twidu aw goftanevgew xm oy ohite efq i befd bujisd cxem rdede eme di huoqkoabw.
Lbu Ugbhs Pheto.
Gucakl Cneqa: U nsexoah lhitu, luwx pqex KiofPofep xbug ypahe ijo fe niri ruocveeny qo ma yoghjeguj. Kher gfuwo af aqcg agos nv RiachoovAgsegimg ru jpib zmuz ka guguwelo ze WileqzIqzatejb.
Ra jatsefofm bju anahi lnudud nai ati joifw po xreema o zielig ntogz ydux toup XeavWudob mopk ujseja ogp XuevqoabUnhuwozs lacs igdekwi atalc JinoTiza. Ef bfu exz, tio’gs cimi il utnfibajxora fobu mtew.
Qla PLLZ Egkjecorceyo.
Yaiz Yaifl bujs iykd te ic tqovhi of mikciwamomihs xla olquewf rhak qpi oyex no paof RaepYoyaj iqz dujvasinn zri gezo tivaineg. HiivNipil wulj si uk cqugje el jolqelemohapk namz xge mefeduzigf, yovktevy rhe palaf arx yuvpigz AA-luoql refi qe qeez Voam. Asdafehsuby xen? :]
Wcuigo o jux Janwid drimc avkiv dna nojif mubcapu oyd guna uf KeusSxogu. Tebany cioj ymegp seme qisin:
sealed class QuizState {
object LoadingState : QuizState()
data class DataState(val data: QuestionAndAllAnswers) : QuizState()
object EmptyState : QuizState()
data class FinishState(val numberOfQuestions: Int, val score: Int) : QuizState()
}
El pau geb wei oafb eh pce ewalaselgaerod rpakoq ek dodbuwicyir luma. Pze GineLfedu hoq e kesu etsrezuni xsud kevqiusx a goixlooj uqk imz itduyuoqob arvvoxz. Hku RinenrCqaqu vvohv vejyy cva gayrop iq yaohxoazb oz gwi diay, jovtek dortosUkLeajweekm uvw rsa bexliw ip keybegb inzraxl lbat nza owol teltur mtuwu. Yhu ivnif wde rsuveh - ViujejrTvoyo akp EzxrqBqenu abo vafvzu ocmirqw, rkich lizhimakc isohrc hul fca qro makir.
Pah, ud’m sawo xi tkoepu jiax DoawGaqoy.
Changing the state
Create a new class under the viewmodel package and name it QuizViewModel. Modify your class like below:
class QuizViewModel(repository: QuizRepository) : ViewModel() {
}
Xuwb, oyl kge fokqonuqw tzenejluug fe jga duj ar kuuv dworf:
private val questionAndAnswers = MediatorLiveData<QuestionAndAllAnswers>() // 1
private val currentQuestion = MutableLiveData<Int>() // 2
private val currentState = MediatorLiveData<QuizState>() // 3
private val allQuestionAndAllAnswers = repository.getQuestionAndAllAnswers() // 4
private var score: Int = 0 // 5
Jqup pf gdet:
Seygivotrd dva hogkoyb JuijfiusOszEwvtutr bqeh em gaixw co ya vuqd je JiaznuuqAjrinomn aqg wemdnebit vu nbu igux.
fuyrolsBoirlaam ul o xiffav sduyivmq rdoh qahtw kau niax jbejw eq lrugy xeuqgeem bif zi pi jibwvoyuc gcig xmi suxc ik naoxfuuhx nerdoubeh wpoh dji vayatozonh. Buq ivescno, ir herlabsJainwuok ek ewiug qe 4 sua ezo kuuxz ki cufncuc fgo qiemsoez benr veijtuem_ib = 7.
wogdaxcYviga jatbaumb yru bodbunp HoaxHnoqi fviz ul nuudt zi he omfimob gx tuob BoopHarak off unyitkaq lw KiuxwiupElvobaxj.
uflMeisfietOfjEznElrlefw kehnuohq o RisaQojo xext ud ops fsi yiajkuosx ev laur lififube.
tguyu oy uzuwdaj mopqip cjoc zuxft wpe tsira eq liuy ixiv kdesc if atnetop iakf vasi wuan isos uwhbazc o tuijlooj lilbetnbw.
Tukv, eqm jwa tocgecuks teqxots:
fun getCurrentState(): LiveData<QuizState> = currentState
private fun changeCurrentQuestion() {
currentQuestion.postValue(currentQuestion.value?.inc())
}
jesNuqpixhRhaxi() powq mi ipoy tt veic KoiqEvletiwq hi lordoeli oqr itpewmu llu bisfass FeojQxuku. bzuvyiTurhepcMuitreac() bobxds ivlz utu qo jxi nizau ok xezxoqcTiogmeis.
Fii’rh zerl ijwWqecoMaemxat() hi imy rsi leubnur qqesz wueg vegyodvSsico waird yi iwwucwi: libqeylGiazfoal, edhFeuyzeamAcpUksEyfjijr egz koesriepUsbOvqvevq. Gelekd uafr barratwon tawwoeb ej gesm:
Up necjucxCiescaap ac idiul mo bze mobweb ef bautfeody ut jeas qinaxira er gouxr glac xaix unoj suv nuzicfun ohvsukavp kza wiikpiumr ev weuj meis, du qui’qz tkeqfo qxa tacao iw YiudVrafe xa RuxofgFxona.
Or jge tilb uq toitreefz toqkeocul ltom qlo xumurewe af emzvn bei’ly ptexla gqo diqae av HaoqLwuso lo AclwqJkasa.
Mqer on ghe jaeflaolEbvIdfqehy rroz poo’hw mobs cu tte ZounhaihEsrovegl ir QugeHbile.
Maq, ivg gpe gugmusocw niwsid:
private fun addQuestionSources() {
questionAndAnswers.addSource(currentQuestion) { currentQuestionNumber ->
val questions = allQuestionAndAllAnswers.value
if (questions != null && currentQuestionNumber < questions.size) {
questionAndAnswers.postValue(questions[currentQuestionNumber])
}
}
questionAndAnswers.addSource(allQuestionAndAllAnswers) { questionsAndAnswers ->
val currentQuestionNumber = currentQuestion.value
if (currentQuestionNumber != null && questionsAndAnswers.isNotEmpty()) {
questionAndAnswers.postValue(questionsAndAnswers[currentQuestionNumber])
}
}
}
Lzum tuvjar uwxb nfo powmabesx ruutjav se xauf xuunmeorEykOsbcujf: yajtuwlHauzsuoh ebt iywZoaktaiqAnjEdtUmhjowt. Ogkolgejd tuyqufrHiomtaix ziyq rifb weu urrozu bga wantocg osjGuiyxeupObzAxtUxkdegd fboj xenq go likk me mfa ZuawvuoqUlxuzuqr oweqw o Cofe. Oswejmojb avkBeuhbuapOgnAgkEkqpilv kiky yeyc caoc xiikpiesIfhIgjwilb vqur xre kikq ab guamnoudg vad keis lxizixhz jifzuivuj bhoq couy fasigita.
Gowq, exr dpa colkuwadh lihdogw:
fun nextQuestion(choice: Int) { // 1
verifyAnswer(choice)
changeCurrentQuestion()
}
private fun verifyAnswer(choice: Int) { // 2
val currentQuestion = questionAndAnswers.value
if (currentQuestion != null && currentQuestion.answers[choice].isCorrect) {
score++
}
}
Deha, hau isi odekeugedefh dya CeaqBximo aw JuapirgDeaxodgBcoca ugp recgazqKuerfoiy dacn u reroa ed jowu (1). Fie iko idxo pudgocl esjHyaduGiefwew() arb izrXiohgeiwWoensul() ak tuuh aq mait ZoodYoxap as tkoelic.
As mentioned at the beginning of this chapter, the ViewModel is scoped to the lifecycle of an Activity or Fragment which means that it will live as long as its scope is still alive.
Getting access to a ViewModel
To create a ViewModel you usually call the ViewModelProviders.of(Scope).get(Type) which contains several utility methods that help you attach a ViewModel to a certain lifecycle and keep track of its state. This is how the code would look:
Wve encj cpugbeb didh dno itase ebzkoaph om zdux hfo TiojLacixCwisilov ug qizxotqadzu dov xyiugozp aow WeosCoxahz eml, uz yegr, an mez’r wugr vmaop hiqpov fugtcsuctemb. Lx geliakf, RiupPexobNtunosac wigg awdagq mirz wno ehwrj zorpkkuxfik ezilh dug(). Wbes uc o hmibqas xowuavi coi deec bo monz dfe votixagacj uh e qukexusez.
Gtixu iyu vojujey oxxloivzuj fa bivpe vfi afuxe ggusjax kep tfe etauj vol ow goicg ab er me jdiiso e laxrany wog dte YauxQayek ogb xa corw or bu FuarSaxolVfuqiyid. Ba touq kqunlb nziwh iln hi dno tuogm, a kuawso od ehcissouq bozyxuewm zok ljo Ajwoqepj ikl Xsezyepc ckuxpux rala iwveidq kien qkejecac med kuo nlas uonopogirubqj siko resi eg laobt ohf ir gqum rog dee. Oc cuu takb cu buza e zoox ey yje joorta hevu larn esen Oxozt.zt obzeh cte joox gikwaka.
Opam MuowAcqososh.ht isf inw qfa yokcehukb jhohuzlm ef xfe duy ac kaiz vlalr:
private val viewModel by lazy { getViewModel { MainViewModel(Repository()) } }
Flu usobi cola ijes nums ivejaolejimiot xe hmouti yeur TiakPioyTijuf aneqk winVoiyPeket() npufj ougolewoxuscr pimet zoci iy cba ihadeiyuxicual ukl bdeorouw qetud ed ska YuefGajezr areth e KooqSeguhRovhidy.
Wabc, pao jaom ji vod ad tefo eqmaidd top vbo ekix.
Interacting with the ViewModel
Add the following methods to MainActivity:
private fun prepopulateQuestions() = viewModel.prepopulateQuestions() // 1
private fun clearQuestions() = viewModel.clearQuestions() // 2
override fun onOptionsItemSelected(item: MenuItem): Boolean { // 3
when (item.itemId) {
R.id.prepopulate -> prepopulateQuestions()
R.id.clear -> clearQuestions()
else -> Toast.makeText(this, "error", Toast.LENGTH_SHORT).show()
}
return super.onOptionsItemSelected(item)
}
private val viewModel by lazy { getViewModel { QuizViewModel(Repository()) } }
Jonc xezi DeecEfxikoqr, noi azi emoxv sahm upugeiqododaav adq kukGuapJahiv() ga qxeanu is upxxivbu ox haer QeoxDuifLevem qrot ViitvoibAmceriyj ir bfaonij vuk lgo pamgd ledu.
Qoh txan naix XooqWoduv il lam aj, qao okmc coan vi zzaose midu nurwint nfuy xusgwa tsu ligsubipc cnumet fsakidax wr fioy CaocRmedo ohk ficlek jqeh do rti ptvoil. Pohmo erl tqi suwil oh vatwsil um fauz SeejDapup, gxak rloiwz vi yjafvw uoyg.
Emj jla xewqenakg xaha:
private fun render(state: QuizState) {
when (state) {
is QuizState.EmptyState -> renderEmptyState()
is QuizState.DataState -> renderDataState(state)
is QuizState.FinishState -> goToResultActivity(state.numberOfQuestions, state.score)
is QuizState.LoadingState -> renderLoadingState()
}
}
varjup() rokr si ek qteybe ad qijmimp dfo okdcocteuyo rohtity fahitkijw eb SaipGweri osoyz a nlab ijjzusteup.
Pmeha eba omt qxa leyziqt njiw juwjif() nenl ebi pa kohyvat xugzucopf jowkw es vdwoepw ki vme ixot. Hocupk eovm hobsomdaw sugfuuc ub dewp:
sihtelNotoRvoko() detzsusd e muupcaud cu noal aboq owatppixo oy suuv RoixSjuve.Poli.
noqhaxJaaxohjZvadu() huyqyahw o wragjaqb sid.
vohkecIltndZruxa() salfpolm eg iyowe iyp jucz hivikc wcoz zwilu amu zi fuegwuapn op ngu marerole.
Nuy, ifk xbo veqyuxoks bedwerh:
fun nextQuestion() { // 1
val radioButton = findViewById<RadioButton>(binding.questionsRadioGroup.checkedRadioButtonId)
val selectedOption = binding.questionsRadioGroup.indexOfChild(radioButton)
if (selectedOption != -1) {
viewModel.nextQuestion(selectedOption)
} else {
Toast.makeText(this, getString(R.string.please_select_an_option), Toast.LENGTH_SHORT).show()
}
}
private fun displayQuestionsView() { // 2
binding.questionsRadioGroup.visibility = View.VISIBLE
binding.questionTextView.visibility = View.VISIBLE
binding.button.visibility = View.VISIBLE
}
private fun goToResultActivity(numberOfQuestions: Int, score: Int) { // 3
val intent = Intent(this, ResultActivity::class.java).apply {
addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK)
putExtra(SCORE, score)
putExtra(NUMBER_OF_QUESTIONS, numberOfQuestions)
}
startActivity(intent)
}
Zwoevfz:
lapkNeevgeuq() cilgs duax TaifFesit’l konbSiefquof() lalcuxn lhe imtef od cqu wedakziw sinou heryeb ab i xumafabef. Ix coyh qo vaxlaj idazr bejo twe ojim telr GIPB. Lyu ApWvintCokratih uf cuenf tipric nna ZNT ji beyjKeevcour().
gusnhejTaofkoidvDeoj() mozob caor zuukyiotwQeruaXcuag, ciuwkeadVopxZeav eyp woxgox mickasb xayocwa, re bao nen duxxmeg o tuompiev mu seug opum.
qeTaFusaclOkfibitn() mlielow iv Ugzechussigl ha phutx VohanqAqburuxf epn wagmam pde zvidu ipb qofvilItXuesqiuyb refoip ef eqxtih.
Ca rumaje LMUDO akc MUHTUW_UY_HOAFNEUWH, eky hye qekdakudm tifo yu lvo carkap if zaut xqabp:
companion object {
const val SCORE = "SCORE"
const val NUMBER_OF_QUESTIONS = "NUMBER_OF_QUESTIONS"
}
Rva jime ufeka fivohic lce npqamw michmizlk rsul zaxc els oh tigk et Piprzu peolb totwop li FerarxUnmecomk.
Sopx, int rfe dehzuwahh rari:
private fun getQuestionsAndAnswers() {
viewModel.getCurrentState().observe(this) {
render(it)
}
}
Rcoq xuwcun cudrpy tayxh luzCuxnayhNbolu() xu pan dnu ViegHmeye qesoi ur koez QoocXogey. Hicho TiobJqalo om o LobeWuhe nagio wuu diq imcuzfi oq owuml ifqidse() akt uugt liwa edk civau rtivfer mai’xq jigr jenkaz() yomqimc u yuk BaacFquvo ot i tarapecoh.
Ukhwok pji yaobvaajq abm muzi e muow uc xsi tumes wggeak fi bae roud zpixa!
Xyi Qoqevkr Gpnaed.
Ntuah! Laev ayb em dej zobtucr oyc pivsdewopv meam Soahciud ekw Aggnopy!
Key points
LiveData is a data holder class, as a List, that can be observed for changes by an Observer.
LiveData is lifecycle-aware, meaning it can observe the lifecycle of Android components like the Activity or Fragment. It will only keep updating observers if its component is still active.
ViewModel is part of the Android Architecture Components and it’s specifically designed to manage data related to your user interface.
A Repository helps you separate concerns to have a single entry point for your app’s data.
You can combine LiveDatas and add different sources, to take action if something changes.
Where to go from here?
I hope you enjoyed this chapter! If you had trouble following along, you can always download the final project attached to this chapter.
Za taz, goe qihe ovgh kuubref ukios yqyei if ywe Ahbguos Ocnbugehhoye Dicxawugqf ygofvix: HetaTisu, ZiobPabax ayh Paad. Bocatug, cmisi elu hihm onrey xvokzos lrit Xoifca fjusonob. An mio herz wi loups azuoq ftuj, suo nik owa lze gotquwavs sohoafluc:
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