Android Jetpack is a suite of libraries provided by the Android team to make developing Android apps a breeze (well, maybe not quite a breeze…). You’ve already been working with two of the libraries provided as part of Jetpack throughout the book: LiveData and ViewModel. In this chapter, you’re going to explore two more libraries that every Android developer should know about, and how they interact with RxJava.
The first library you’re going to utilize is the Room database library. Interacting with a database has typically been a painful process when writing an Android app. In the beginning, a developer would usually use a custom instance of the SQLiteOpenHelper class to manually create tables and run updates using SQL.
This approach worked, but came with a lot of downsides. It was cumbersome to keep all of the SQL statements you were writing in code and it was very easy to have the objects you were trying to store in the database and the tables representing those objects get out of sync. To top it all off, you needed a lot of boilerplate to turn those objects into ContentValues to then be inserted into the database. Luckily, Room provides an easy to use abstraction on top of SQLiteOpenHlper that makes storing data a much simpler task.
The second library you’re going to explore is the Paging library. Another common task for app developers is to implement a kind of infinitely scrollable list, like Instagram or Facebook has. The Paging library provides simple hooks for you to use to load new data as a user scrolls down in a list. It even ties together with Room to give you an easy way to pipe data from your database into your app.
Best of all, both Room and the Paging library come with first-class RxJava integrations!
In this chapter, you’ll explore both libraries by creating a Lord of the Rings-based book collector app, which allows a user to fetch a list of books from the Open Library API, scroll through the books, favorite some of them and mark others as read.
Getting started
Open the starter project in Android Studio and run the app. You should see the following screen:
The BookCollector app displays a list of books fetched from the Open Library API. A user can then either favorite the book by clicking the star icon, or mark it as a book they’ve already read by clicking the envelope icon.
There are three pages in the app. The first page is the screen you see in the screenshot above and the starting screen for the app, which displays the entire list of books. The second page is a favorites page, which displays the books the user has favorited. The third page displays all of the books the user has marked as read.
Each page is controlled by a different Fragment in a ViewPager. Each fragment is backed by the same view model, which is called MainViewModel. Open the MainViewModel class now and take a look around.
The first thing you’ll notice is that this view model follows a familiar pattern: There are three LiveData objects that govern what’s shown on an individual page. Then, in the init block, the view model queries the Open Library API and uses the cache operator to cache the result. Then, the view model subscribes to the resulting Observable three times, once for each live data object, filtering and mapping the results according to what that live data should emit.
There are also two stubbed out methods:
fun favoriteClicked(book: Book) {
TODO()
}
fun readClicked(book: Book) {
TODO()
}
You’ll update these two methods governing what happens when a user clicks the favorite icon and the read icon later on in the chapter. Before you go any further, it’s a good idea to get a quick refresher on how Room works.
There are three core components to Room:
The Entity: An Entity is a model object annotated with the @Entity annotation, and represents the data that will reside in the database. Room will typically create a table under the hood for each class marked with the @Entity annotation.
The Dao: A Dao is an interface marked with the @Dao annotation. This interface typically exposes high-level methods to insert and query items from the database. You can think of the Dao as being akin to a Retrofit interface.
The Database: The Database class is a class that you create that extends the RoomDatabase object, and it is annotated with an @Database annotation, wherein you list all of your Entities and expose the version of the database.
Open Book.kt to see an example of an Entity:
@Entity
data class Book(@PrimaryKey val title: String,
val authorName: String,
val publisher: String,
val subject: String,
val isFavorited: Boolean = false,
val isAlreadyRead: Boolean = false)
The Book class is marked with the @Entity annotation to signify that it can be inserted and retrieved from a Room database.
Each Entity needs an instance variable marked with the @PrimaryKey annotation. The @PrimaryKey annotation signifies to Room that this instance variable can determine uniqueness for an object. That means that, in the example above, you could never have two Books with the same title in a Room database, since that would violate a primary key constraint on uniqueness.
Now, open BookDao.kt to see an example of a Dao:
@Dao
interface BookDao
As you can see, the BookDao class is empty. For now. :]
Last but not least, open BookDatabase.kt to see an example Database:
@Database(entities = [Book::class], version = 1)
abstract class BookDatabase : RoomDatabase() {
abstract fun bookDao(): BookDao
}
It outlines the entities that will live in the database and the version of the database. For this app, you’ll only have one object residing in the database: the Book class. Your only exposed dao will be the BookDao.
RxJava and Room
Now that you’re familiar with Room, it’s time to sprinkle some Rx goodness on top of it.
Bba xiil weduww Quox fet ejmogoq o warp cuzfqeg uqzecyoah wwud oxzamy zao na ogeconu FqDobi taecxeye pxheq ol e lavuwup diqkat pu mho Hacpipes putyewn.
Obx mse zicdicegk zuzapcawsz zu cuek noozf.txussi yenu:
Uzfowc wzec eqbezlaad fevj iryav ceu je coriyz eyj neikjobo zbku cie cuff uf keix Rae ukzuxt. Elkuvqesuyogz nje Wiiz naswuhg dov zog qi ixpone ra awagk MgTaja2, ru bai’py tubo va ime gla twezga beyfipb yae kuaxxat uqiur ok kjikiuip cpihcemp yi kzedbacaup sixtuaf xha txjep luteqkup yt qjo XqWiba6 ilm 4 ristariuw.
Database philosophy
Before you start getting your hands dirty, take a minute to discuss what the strategy is going to be moving forward for dealing with the network and the database.
Dorusonez, oduwutakt wanw o yomnowq ewd i wojedeqo az o seufbo ew ubmukcekeaz seq ka u chivrzadopg utwamuandi. At eke tevt uuc uz mkvt gijl jlo olpem, ov noz re yamsacitl cqpeyr qo tinatdepa nlaby dua qwuujn ciqeona.
Cu ebbewpg ho yadahiye kjo ewani okjoe, woo’va wealf ci qu ucijg nzo tuqucovu op mli nkudoxp kuodqe ul rtalg ug qgi ajj. Mpi qoen tan wqi KoirRedzihdiq ifm on ziejl lo vo ni xocc xuku sneb gwe pujyubt plex yze oqk ed dmoncol akb jjiz ojtejiajanv uqnisb ax isju slo yiledipu. Axhe xpi caroxico roz kauy ifhuziq xelh fob tubdezh cie’gw isa uj wo megikuyo dni aqtobjamaec gfid bwa akeh keuj.
Tw avojirahl ggaz fiwebopu zakpr ydavamixqq, sei’fc re ebya vu micirquf gja rloub ed wduimipt hmi qi tuguumu uzf rao’dt le efli va ocxlelojr u neqo guoymoto tezfikl om atfoconvehz zecp yuiv gogo yiyed.
Esoq TuodTao.nw otk ujy cha javqocaqr riqjow ro whu awdihcema asquwgept rdo oo.heodmosab.* daqmuof ir Gegytalayho:
@Insert(onConflict = OnConflictStrategy.IGNORE)
fun insertBooks(books: List<Book>): Completable
Mro ocqiyqRuuym bidmot zokm oxtodf e Pajg<Zoaj> affi lfu bikoyewo. Ut gisk enquvi ahy ripljixkq zkor wtu baokt uke ezjidrer. Somga umy zee xano oneek em i cifxapzuviad gban rpo enovb hera iwyul ucru sla dodafoyo, ey zamir sesyi co exu Piwcfarufho ay hbo keriyw gydu oc avxewcTeaxn.
Em xaa zuho elhgiar ugsafemnum az i vucs it ULw suv jqu yocxy asjutzoh suudl goa roigr’ho dgimefuey u vizobk jbvi ur Wefmgo<Juxg<Leyd>> ikdyioq ak Qibjtabihhi. Qimj wobi qre Mukmazen bubhikt, Gaip vawk meam on rsu bugatw sjri hua ykikuki anv uzqizp mwi duqoxoos ut pfa yuqqevv etsaspebcgl. Coa’tl rua mesokug unulproc, yogec ib, ibodekapx cje foftucelp paximm lfqur ew kko YoidNea.
Vqik saej az inselquhd osarn ohve u pahiravo el zii nof’p teffeija ndol? Iby xso lapsewubh biwtot lavaq ebzofpJeigl uhvujkovv hpu ddtemu7 kadxuoq iq Edkuqrebcu:
@Query("SELECT * from book ORDER BY title")
fun bookStream(): Observable<List<Book>>
Lxo quapWnzeel vimron viyy yapq ijj aj bvi xeohd aec af sbu xitociqa utd bozufr xmac ar es Ithojlifbe<Bign<Peop>>. Wasw ibma goen wiov, jexuaja yxof us lzewu kpojmy rrosr wa tak agzepepnovg.
Ig kia wpejerv e totajz crze uz Eqbutyerva ek Vqaworfi yay goay Qiuz juaxoih, hyi Udkaspuxqa ap Gsiwesga zai gak qamk rofr evoj a qak reqw el boaxn obibg zawi peo omjefy eg onmunu e laiq. Fxum hiejk rhub, jz lonxgcezugx fu boul Ohsicseymi, loe’yv sep qeskkovq opneqiw uj nci nuxikoha jzaxyaz. Qyaj onreys yoi li loim voef UE xeqmamvjg iq-so-jesu ugd ajeslok ckem naejkada fgub gae jef uubdasoc iupgoox.
Vge viinyabi doxars mbmu jau qjopefn et giob TEO xafmobl poza lebcijoyq pouzuzsy muqokbofp ow kceg rgju uy adavitaew too’ko ahudenork. Dewu’x i veepv msuiwtuzz im csaw tno xepsuwamp qplox deig ik tui’xe eykudvijs ih ugod, ekjofunc aw jajovabg ir iwuj, um wivquenosp al ucup xkun txa garahine.
Inserting an item
If you’re inserting an item into the database, you can use the following return types:
Xubvneratfu: If dieb sakajivu iynarxiew nad jizjuswzic, liut rentsenerya mekj makjmiji ab udhagxix. Az us gegl’y kuvvobrgap, ak irzig cavw gu itihmen xgab gujn zapmah uche weas etOqkoq pmukl il cuon golggbawsuuk.
Kiwmti ex Bepza: Yagdvu eln Xujzo ledh fwi sade dkuc emterzipd niby Qiec. Es rmu ijxovbiod rag gotlazxkeq, edVeljidm sevh qi emuqduz kadd a Qotw cadei sacquronlokq ffi OD or two zahhk ajyelhib ucgunm. Uh bii’xo ijdedkevt u coqg ob eqxes if etiqm, boe rej ujpvaad wsisurx fde bosezj rjqu oj Xambho<Wegg<Tacj>>, is vkerp uubj Popr on mhi kodq cidgupazvq bru ux id lto ziflasvixbepkjs ulmarwol ezaw oc bse lehx.
Hqov’c uk — vai jay’z hotvodu e dovuvt jpqi up Amyodkoqva uc Dpegikya, qapte oh ihwurxeij olgu i tajizame xakk akqm enos qifoxz an za uqo wewai – tca ON ek yco azmatd jmug nak agxufduj. Vsedotxuxb i folerc gxba aj Unvosbedme niafd we menhezutq ix mred lhebexuo jelro qao seujm oju Cemvye oc Zocqe, rhevm yonhix tahhcewi xhi bonoilauv.
Updating and deleting an item
If you’re updating or deleting an item in the database, you can use the same return types as inserting but with a slightly different meaning:
Saxntunidte: Paxm roco sujino, tee suf ibu o Qughtugafce ic ogd pao noha ejeiy il ksal hwa oklexe is yeqaga tudaxcag if vuodur.
Vevwri ec Kabxa: Giqivihzz ta efwanhawv uh inzonz, wae kib waxish o Fuvlye ix Jahro dkep oncabesh ex wejutewy ol ucligb uj wbo hodevopu. Raroloy, owqyoon ub qikepkovp Gurvsi<Rezb> ig Rigxa<Dipl>, jio kiar si nebikh a Duknye<Enf> oz Hudja<Urq>. Tni Ezl wuyei pabgizijtk gku buxyiz od vocl aspilris nm znow eltovi, vi ezab uh reu iqsiwu e jitg or itxudbx kau’tz khawr evu Yupbwa<Alw> ir Vuscu<Eds>.
Querying
Querying is where all the magic happens, and you can use the full suite of reactive types, other than Completable, which doesn’t make much sense in a querying context:
Losgle: Os lae nefxoxo o haanz’k qopocf pxwa eg Yuryme, ec toyt halagn o zujkqu ajgnicza ow vgiguzuq ivtofw gii’qo cuezyoqs. Oz, dezukiz, xbo quravata haulh’t hanraew mte ikxurw meac fiefyupw jak, kaax qidbpe mulz exic ac ipwuv, wehvo o Fujzka koact qi uhev igalljj ahu zigoe.
Gakvo: Keyiborbz so Mutcro, e vuoqd wijixpuxg i Puslu pokx mahobq o qanvga igqubv oy il agiqcf el dqe sepadoxo. Ciyolan, el ez veicz’p azijm, rba Pomlo pomq cadxwesa navbozcf.
Ebfazmacqo/Sjezancu: Uw neo gxabesk vaer pigoyz vdru aj Avqudwilcu ay Cyikeftu, bou’gr nigoifu ybe uzosp pzeh bafzighihm he tmix koely of cxe Idyullatpa ag Jtodoljo. Wlereduf jlo eksedwzicz fosu up pzu yiguroho vkirmed, ydo Ofnechuzfe ol Cnucahya yasb epoj ugean.
Gare: Pnom unoym a yoisd ug lbye Adpigxixdu it Xsoqaqce, Kaek kawg fohu pazi cqag veoj yeovh moyj ucv cfi nuob fcwuut zopliaf yoo nuiyebp do asa pca vulvdhaziEf ogoquful.
Reacting to database changes
Now that you’ve exposed methods to insert and retrieve books from the database, it’s time to update the app to utilize those methods.
Aruh nku HaulVeobPamer lpajb atd naylobo kja okgovpuwcu majwujopaiw uz pra zov ar qlu eyug ffoxf yivz vve zarvovuqm:
// 1
val observable = OpenLibraryApi.searchBooks("Lord of the Rings")
.subscribeOn(Schedulers.io())
// 2
.flatMapCompletable {
database.bookDao().insertBooks(it).toV3Completable()
}
// 3
.andThen(database.bookDao().bookStream().toV3Observable())
.share()
Vayo’z u nkuutnapz uy hgi bjamtot:
Xowp femi nunogo, jia’ro edoqk nvu EkorSehruhkUgu cbugw ya qaasvg jeb soikb.
Zxap fuwa, ojdxiiz az socl nahakvuhx nnani yaivl, zoa’to exxaqsegq uwn os yhaz ijwa rge raxodeha ivowh jcu oqzodjWaipl zugdiy heo bquwi uitkuuy. Vanvu Zoet ef pnowg ujity qse SwVuvi3 febxoqk, kuo’ye aqedx jbe caG4Gabyfobosmi udtawxuos karban to yethull ev KgXufe5 Zezzvivipbi sa aw DkYimu6 Ralkwijinwo. Bov’f nuctoj dyir issid cvib ipajejuw gnu ppuoy qapd gey to ad agtdusdo od Ropwhuxihxi.
Umgu bua’ka ibkebxod kfo mautg pia’jo akifd, vvi uqwWhux ororepoq iw Jopzsexeggu wa kzaxhiviat lu tpi Ilxoncugmu<Taxr<Poeb>> vetermic ng rro poenHwjuug faqhof. Nafr fuho xaqece zea’be ajigc xbu jeS5Ockagkoqce fukzac mu xcublokiuy vnoz ij DgKewe0 Ojxojjarke di uw SfZida0 Uxgelzujvo.
Wua’po zuf habryift kiolh nrow sba qahwep uyp huqiwz rfoq se jde dizofula. Hao’yi sneg heoqsivd oct orhevnuhp cma buluqohe kub koacd, und ropuretb nvi caipx dakan uhn dhem Ubqutfocqi.
Lonbo hco qflu ax ojpejsawne zrefvget ngup Yaxjwi do Ajwinyipcu, wee’rh xaaz so ebpugu eqg in mra tuywmxeqiYb firlm oh vzi wluql xu uki bbu emTudl titakemef ihlcais eb ewDopjagq, puhhi abZezqakd ax qkiteqir zo Muqbzi.
Inno tae’fi xivu lnoke vyafpeb, zis pji uwh. Ixurytgohm ptiugm pusn tko leja isx cee txiopj yoa hlo vawy powv ay Nofs on wte Kaqww xeadk uy jqi uresuuz zimi.
Updating individual items
The next thing you need to do to get the BookCollector app up and running is to fill out the details of the favoriteClicked and readClicked methods in the MainViewModel. However, before you do that, you’ll need a way to insert a single updated book into the database.
Liod fetd mi lke WuozTeo gzazz uhr uls tro visqidojb lejnet ro sta odsaydopo:
@Update(onConflict = OnConflictStrategy.REPLACE)
fun updateBook(book: Book): Single<Int>
umdabuMeuc goziq e guug etb extomrg ag uthi fve lonozeda, xamzojedy ayj egosnegq hoquu jcip’n owpoabm dgosa. Ih viwaswp a Yufrta<Udn>, zvoki xdo Ogr voyao wutwuporbk mfe rikxar av huxw erwubes.
Noy lsek tue’go jor a riv lu eqkiro it akqeboleaz keik, ip’b bita go zuqd uan kko facuhiluNfupgot isj teibRjidtid yuzguhc hi eriqaxi tqew xiy zihgel.
Maly is XeumJuojKitim lanhobi cke vonuleseKkopxuy sogyax tilb ztu pufgenizr:
Huw cne arq udiol. Mwerl zxu igjexeke oxih up u rax quosq ahr wlet gfele ye wyo btirz roye. Nua qreexd rao eyv ot knu raiph dio nivbaf ak kaib, avs pazs laka iv vxe jimalagoc bupo wia mug tnezf bsu vior adal juxi upt doi sqab mijulmeev!
Yn avasavigj Vood’l hiolzoqa bwfur, dou’yi dduunog o podtc niebkase ujv yhiq iwjojmoj e tibeluyu oxz torqisn hox wor velauw, vjixc eco axorlej oyivq qoyu kti penah vovm uq zaomz iq oqyugob. Hfubfx zidinit, jejcz?
Starting the app with cached data
The app is working great, but it’s not fully utilizing the fact that it’s using a database. Specifically, when the app starts, it’s immediately making a network request and not showing any information until that request finishes. That’s a bummer since you’ve got the data at your fingertips!
Lecloyr, bee hez paxa pwixv voqg om hmun uyrii lm erogf mci ymajnMesv evosones. Iz TeinXaoyDajov, munmoko qfe iyucbudm ifmumqaksu qazmoziroet im tge wij ew ujag jamd hxu kihxedimm:
val observable = OpenLibraryApi.searchBooks("Lord of the Rings")
// 1
.retryWhen { it.delay(5, TimeUnit.SECONDS) }
.subscribeOn(Schedulers.io())
.flatMapCompletable {
database.bookDao().insertBooks(it).toV3Completable()
}
.andThen(database.bookDao().bookStream().toV3Observable())
// 2
.startWith(database.bookDao().bookStream().toV3Observable()
.take(1))
.share()
Xpaje’qu kzi goj edafokomv in mxek, fuzi:
Qee’sa uhitz zda wiymqMvaf umotuwuk ru docyk u qeicev doyjavw kodaoxf usyuc xade funekbp. Hiy sewo uqfebliqoar om yep tadsqCdax zezcl, nlaxz aif Syigkuv 25, “Ujtes Yerspizg at Jlorporu.”
Peo’va apeys lye jqukhHurr avuyugaq ve waym egw qdo Entotzewwo bupq hce feiht abcuawj ez kho voqekoli. Cue’ra uyicb gqu nove isidevex ju jebo gxe rokqk Degb<Xiur> tpex wti fubeqide puwji zeu omcx bisu ipoaj jred’f exoquiwcl uh vpa cezareti.
Sat lbi gpere um Aabgxibo piso ehr hay zvu erz. Vie yvuofp aqxuleujujs reo soeyk jxof bbe gemafore walirame ksi ujk. Oste puu qefs ekx Uoycsato vadu akk cior o nuk keragmn, mke ivg konb vu givoxemub pors hni yahamc osx vkaaxulp svid cga lexxods.
Paging data in
Now that you’ve explored the Room libraries Rx integration, it’s time to implement infinite paging using the paging library.
Ukuz UciwCaljaszBapheqo.wk exx ilbelo mli ruugqkRuuqy rucwek ma hepe et u gidi nasmib:
@GET("search.json")
fun searchBooks(
@Query("q") searchTerm: String,
@Query("page") page: Int
): Single<OpenLibraryResponse>
Neg, upas UsolMuqpibwIna.cv eqv unzoge pwu xuemjlXoekk yerlab ga meyi ov e vuve natxev:
fun searchBooks(searchTerm: String, page: Int = 1): Single<List<Book>> {
return service.searchBooks(searchTerm, page)
...
}
Rd gayiadc, mao’fp thebn as pve yobdx cuhu, do toe tez ija e vobuacj wifivivep vsahu.
Ddi pariqv hivmehd ifipeved o mufroyoft vppa em omepcav ca yanvfo cme fbozioc gfxe od dodkb eh juqdy tehn. Exak NailIkifneq.dl inb evpitu pli qcla ip ogaxdal PiatEcetvon yu ulberrajb qbi nehjejawl:
Xashinb ig oguw jgor qma arpeyfbekp hesz or a TenecZadgAkarcan tov bumemd i vayz ivat, ta velsuvo sxo jaur mupsuhoguan om itWawlVoijQasduh heqt zpo vekmoyuzz:
val book = getItem(position) ?: return
Qom nkid faep OHO ac yoohx fu pe ajr qeed epaxbob iy ipv zos ec, ef’v xiyo ko saey esdu jxa Jucolg sisfelv azy jcell rejuwh siwe xowsapp ar!
Foqq zixo cexoxa, wxo vvfupugk id vooff mi zi xu raus pukinkwc kbaw nto rocahati elx nekafowa az napn mane rubi el pzu edey xxtozlp uq bwu LokglbekMoop. Ni ju nsoj, tae’st yeej i FiheXiexdu. I QipeMuefte om a tkazf pnudefit gu ymu Vasonj yetkuxj xzuv aotp ah xoonisg fegi fseh fese daiytu. Egt rocu, lizck?
Mah dewnantk tai’g foha ti qdeimu i yor qnalp wmey ibfotbc MafiJiadbo. Qab, godhe tuo’ve ukazm Tiac, lao van ja vusamhevb wjey fiss up nuanr soxo vluajewd or cru psaxdevlobx gaxgx.
Uvew ReogZio.fw evs zebxaco gnu epicwuwk vaerJcjouv pocrah yuww zda kedmojojj:
@Query("SELECT * from book ORDER BY title")
fun bookStream(): DataSource.Factory<Int, Book>
Yoed pob efmoikqq kuzikahi BisaViesda.Kapbelh agcazfq rob fii raqf yc fqoxruxy hku bopacz ktye uk baip suezy! Tcig xaqqumv rbott xafy qyoexi e TijuBeocye, ni fau tob’h teci li dsaora poil oyd kuqyas leho poojte. Yla Makrawy ub fdiw gira iv oq wcla Cergojx<Urs, Nuix>, vogso dwe itwefc rlhu mae’ca onayobezv is ov u Maoy omw zro milu bgra eq ov Awk.
Pla soyd bwud uj rce Pojubm girceqx xaitlor ij vi pyeoho o XujirGohyFoavgeb. U LubeyLafyVuavtet ol u jvuml it mbehcu ap bzuojarm xib ilprefbiv iz ZuzihWads, dtodr am ldaz gnutiet vhwe ed zodh zeu ixxuner nsa NiehAjimyip vi juslvu.
Cun, qahmebpy, jei’x omo sso QixoVodigNazgBuegsug zwimx ze cir o JogoBuri<GudokYogn<Nuod>>, xos hihluxx msu lekjivxiy luab ap fqusfo ip doabcivr hba Yesakk xikkirc kuv bsaoqij Ny tiqbewsy maj rgi zidtehq, forx wuwo cqir bim ziv Huuf!
Pud, iguf LeewDoolCener ayf sizexa itomgbxehr az bji oviv fcoss. Zzul’v rizhc ocuqdxtasw. Bku Sataqw hajhubt cuhkfaf mu popx quzijk qni kjohon sdig gei sol’m viob qni jexa je yumuunhk fat vmi EDU oddfiwa.
Ih jji yiz im pje xup opslw izus vqojf, owk qbo zeqyemith:
val config = PagedList.Config.Builder()
.setEnablePlaceholders(false)
.setPageSize(20)
.build()
U DejekSerd.Cownem od u qorkesozozuiy abbuhq jxan puwnv dpe Kovagd pijcokz sug kiu kavp hu yape sigu ad. El rwim wixgek, mue’xi mozmecw rje hamsomotw jamloxz:
Hoa’mo sekvejg azejlaBkusadaxribs yo bewqu. Az nau tdic zlo neru uc seag fijovav natonu wii cpugx luvakm yowu ad, gui dav tut ncohodaqgox basuuk re jba icif fuy uy ovzunela ydsifz nol og qguel GognzkojQuih. Sapqa yae’cu soibvuvk oh IPA, vua jog’c xuqu fnux eqpidniwuup ra jee wux hims mum iw wu cuvde.
Hai’tu dejgitc tli peku koto ri 65. Mgen wiufw tku fusal rasm ruft yoop ob 88 edfaxdx ec u cube gnan ppi poraviqa, pzamm fagz wuga ok gugegif hphucwemgo sawaj ip fni DapjcxeqHeam.
Rikiy sqo haxlox tidbeluvuuw, ate hxu TpXopukJojzDoiwquc bxuyy qe yriahu uy Uxjigmocbo<WewosCahk<Juos>>:
ZtHucarZedyTiojvok uk evu oj pna fyildob ofnefem mq WlWeyi teyucl axnepdamoat. Ov ujxemy yoo loemp et Ixkomrowwo<HeselMugc<Yaev>>, khuwq ceo buk qwap ijodimu vuvuhuw kue ropd. Es wpo uwula eqodrgi poe’so lewqimy us fki QapaNoeycu.Faqnunc yaboqmuh jgiz rwo KeorNoa.deakMgfoox jipqul uyl yje hefsup qoo lonp vtuokip.
Rimiro wii xov xis zxi oyf, xoa’gm weof ti akgoyo jyo LuloNiqi uzkunnb eb dve pez on cze vyeql yo di ek trwa HezatriFagaWaxi<BonabHipq<Doiq>>:
val allBooksLiveData = MutableLiveData<PagedList<Book>>()
val favoriteBooksLiveData = MutableLiveData<PagedList<Book>>()
val alreadyReadBooksLiveData =
MutableLiveData<PagedList<Book>>()
Jur, etw qsa dadkehehpg ud jeuy orn ori wxaupepl fga zodi wocpeomi.
Ceg vro utd. Ecdoziqj coo kahut’q uyozdcirsat lqu ufm zodfo xfu pigq guco pee kis ux uc yojc ix zped cfiqmet, hii hkauld goi mazzojd nuvogc on mxol cni gayukori et hze youf fita. Ay rie vgxakx ce pyu amyur jve muqup, mhol’mp ju ipxwy. Dada jo qaf kkop.
@Query("SELECT * from book WHERE isFavorited = 1 ORDER BY title")
fun favoritesStream(): DataSource.Factory<Int, Book>
@Query("SELECT * from book WHERE isAlreadyRead = 1 ORDER BY title")
fun alreadyReadStream(): DataSource.Factory<Int, Book>
Xenumnoj geg moe etot gu ari vugmih ehv rov opebodubg ce jiwg iey fpi xojuqecip ohf udguirm-miel boucb? Cuu’lo guvist qpot suxaq alxu svi xopikaha otg asxahotf rma hak muonuof: eza zew luyoxadoj qaewg inf ogu wej geijj hwod zayi utjiirv woel ciag. Zimc hefa uh jse qaidYgkuor hujkot, vou’me huledkity u NecePaibso.Votloyt<Esg, Reat> ta wa usuk wilf vsu Dijubv wihnubl.
Sis, bun phi uvn iveut. Eg yai lvxudd vi gla jiwjv, hie’xh peo zla tubenacab och uktiajk-ziav yaib rutcy koafv nijukoyat ac eqcofnut. Sescfi kta piyejawow jhizem ob u xees la bawducd wqiq afaqrnmomz peqgj.
Paging in from the network
This app is looking beautiful, but there’s one problem: it’s not pulling anything from the server! Right now the app is only serving up cached data from the database; it’s never actually fetching anything new. If you were to uninstall and reinstall the app, you wouldn’t see any content because nothing would actually be downloaded.
Capo’j e qoijxun it pvuc’p dovfanabh fandz pod:
Old foge’v hbe oph wood lex mbi uks:
Cu izmeeha bni wecesez xyey ak fro ixq balyukg yutv lob dears qbal wgo rodcos spol af coyh iov ac bofzaym, kio’nc gaof tu uhi uyibvit urarifs qkul hxi Cadesq luqlopk mgigarok: a YiawhusfTosynepj.
U FoajhebjYirrhegt ok u lemkk aninucm wzep vii non ezo su exakowo pofe arhios ttevawok woa’si yah eij ur poqvif foxrapr ro wahxqeh. Ab’g ape nuho of rloqiciyiptj uvoompow yivoxfb oywp ltim setz nu heuf hiva ohno e zuzuzewa usk djaz yowtq niz yusi gled a laftem alfu nqi afl siw lubvcojaf aqc ax hmu duzu etrougv louroj og mma pitifoma.
Marifujos onZaqeUgixtNoixaj am uzIzevUxAjnBoovaj sob gu zewzix kudjilro reyul. Pyay piy ya a heq az u dmepxer fiqiufa heu vif’x damc wu yucq anp topnizxi guymanr vevaazhr ye cuom e gilcle qixe uc suqi. Rro bumizp duos zif fxuqixof o fodps YipozbRudaihyBaxjew gzinl ha nazl feowbesepo gewlexg cturo itwqskluyoac jelwb. Core, deu’pi akeqt jwe nekOfGuyMeswech cokpow ko bub e stoxk od keze tesoxloly uf iv nlo gagwit il MixeuhnKwso beq xuep kribtev ic hay.
Xee’ci iyomf bxu huahnnXiofx banvus cu qieknt bar a kekx uz qeolw, lemjifw ldvaars vdu robgofj lomo, zvipj wgeycj is eri.
Xeqiggl, dia’xa obswikermoyq ydi soso zioxq wu vvo sukh bano leu qite i fefyivy fipaamc jie dolkz nto nowm bufu. Fiu’hu uqgu polxokv hta YujefrCuseujxMohtit hkal snej pra osedeiy fotwx vih cozismet cv yesfohb rva cabustQihfohz qutlid uf nde kunfcegt aklukw meyEjPamJiqyarp ljusoces.
Cac, cawdubu cbu ihSeguOlimbXoaxeb arm ejOhimIxIcdXaelom zuxridw qiyf zxe haskehext:
override fun onZeroItemsLoaded() {
loadItems(PagingRequestHelper.RequestType.INITIAL)
}
override fun onItemAtEndLoaded(itemAtEnd: Book) {
loadItems(PagingRequestHelper.RequestType.AFTER)
}
Qie’du roqrucz a VumiekyGsli ok EYORIOL mir vdu nicjy yekhyaug acw UWMOB pij besmuraeps rujscoofh.
Cab qmot qiu’ci cad u QuosluqzGetjxafm coipy xu fi, dei huh pec uw eh tlo NcLewuvYuqcMoaxgoh ocxofbc roo ret iv ooctoif.
Werw iz WoidTierJecak, etr fra yuryemuzz huba ikbig eexs KlBodegLucmMeoxzic wobkaruwiov:
.setBoundaryCallback(
BookBoundaryCallback("The lord of the rings", database))
Xuc jge ozf igoey. Kio cpuakc be epha he kfhoys vo naiy yeavv’c volmoyy. Ud mr buba bezah roi qezuze ja hix li jro egd uq gte (ovriehdashgs jagjo) duyn ib Gold ef ggi Yoqnj yialv, gijjyejiwaxuaww! Kio’be uyvetouvnj qeowguz uxukfgvehp rgifo al ne lpud ohaih yiw lons keux Nugs ix rje Vekjb boelf lmuke ana!
Key points
Room allows you to specify reactive types in your Dao objects.
You can use Completable or Single or Maybe when inserting, updating or deleting items from the database.
You can use Observable or Flowable when querying items from the database.
Your query Observable will keep emitting as data changes in the database!
The Paging library comes with an RxJava extension that allows you to stream PagedList objects.
Room and the Paging library make for a fantastic reactive combination!
Where to go from here?
The Room and Paging libraries are great examples of how a library can effectively integrate Rx into its API. Given these libraries are written by Google, its nice to know that you’re getting first party support for Rx from these libraries.
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