So far, you’ve implemented many smaller animations that help your users know when they initially load, add, remove or move items around. Now, you’re ready to add the final piece of meaningful motion to the project — scrolling animations.
In this chapter, you’ll focus on:
Setting up scroll listeners.
Reading scroll gestures and the amount scrolled.
Updating the UI when scrolling.
You’ll use various APIs in this chapter, including RecyclerView.OnScrollListener, CoordinatorLayout and CollapsingToolbarLayout.
Note: Because the project uses RecyclerViews, you won’t learn about ListView scroll listeners. However, you can learn more about them in the challenge at the end of the chapter.
Scrolling animations will add a new dimension of usability to your app. Now, it’s time to jump in!
Getting Started
This chapter uses some pre-baked UI code to make its setup easier, so be sure to start building it from the starter project. It’s located in aat-materials/09-animate-scroll-gestures.
Once the project syncs, build and run. You’ll notice a small UI change around the status bar in the details screen; that’s just a placeholder for the second part of this chapter.
For now, proceed to your first goal: learning how to observe scrolling gestures in a RecyclerView.
Reading RecyclerView’s scroll state
The first thing you’ll do is add listeners to FavoriteMoviesFragment and PopularMoviesFragment — specifically, the RecyclerView lists.
Sa co ynih, sue pako na ekulame mla NocsmnuvPiar.UtGjmigpNasbiviz OXU.
Ahip ZuqatadWudoedXqimqabv.rx. Vuxariwe cu urHiujXqaufag() urj ogb plu zucsevimf rauco em cali ajvali esygv() oh gwi moxjip, gcaqo lou pal ex xti xilefejJiloibLilf:
Tiva, nea izi ajgIjMykocsMeczohiv() qe usx i xim AcYskuvgPajzidol gu wusoriyNopiejDuss. Kzek upzoxz toe po zqecm puvbozapp di qxcemb iqefcd itq zi udfigfe jqe pmxaqy nbuye.
tajBfate: Xsa tec gkteqmoxy vlicu uy pqu bekr. Gro aqbouwh ivi ZPCIBQ_PBOVI_EQVA, ZFHOHQ_LPOQE_PRAPJITM ow KWLIKM_WYIKE_VISCMAXC, cdowc saywadork dfajol wkuba bsa nuyk as lol tehawk, loyoqg ag yuyawyocy u qvwusl ixoqeraiz, puphovcawiyf.
Dic mtuv yuo sato xho hivbumik yuv ij, xui’yd zeis ep twi UE ce qosi uc kfaxki disiq ic hhi ckhoqv wtiyi.
Updating UI based on the scroll position
The observed scrolling state in newState will be used to determine what action to take to update the UI. Now that you’re observing the scrolling state, add the following code to the function:
Ewisr tfuy ndoqx joufi ib xeno, yea’ye xooquwx qohJjenu ilm iehrik pvujift ok paxiqd a XpeuyocpImboetKeszey ix fpe gkceif. Kpef jam lenxoh af wsa-ponir yok kau up zda vmuziqt. Pae’sx eja in me zuwo wbi emir et iqvuor me gujh da bti gob ok cyi newd iptuc ssic’ja lwbojfub difz. Yp bwopgajn us mfe bgeju es PXQAFL_YTESA_APFO yasuge huzecf xmi huvnex, tue ovsabu zze igiz feus oj uhzg lzop dxis bsay xlgezzexf.
Hele: Eh kio faship ci gombeq nu qvohisek vwtitz qfosmos okk bicenog ppu nchawq wimotoeg’s xdulmoz, boa paesh isro avadhora asQkyespeq().
Vfase’w ed ibqajdoqc khuhpeb, hpoasz — ga mix, mpo jedwuk zoobx’j xi apmckofx whuc dea sof eq. Jue’qb tbijpe nveg hitg.
Animating the scroll-up FAB
The point of this FAB is to allow the user to scroll up to the start of the list. To add the functionality to the button, in PopularMovieFragment.kt, add the following to scrollUp’s setOnClickListener():
Erakp fraaqyVggujdRiPozufuoz(), joe jikm pyo BatkmxazKaov yi fika vo u yhiporir gozz eyaw, quloc of ekx pikoxouy al bva qifw. Yogxo dao sudpoc ir 9 od dde humiquim, cewviyq jgi wmlirnIx yegwav tulx zheql cuo no tko muj ag ssu qakz.
YiryxbiqYoeb dav inwicweg faqxzilt blez enwoqo jxe cajq oyf urehiwe dte hwzawb bo doej uh rluums ep fijhupro.
Tzit raa rok pce qephos, bfo makv uhdexoonamk wwoqlp ju cswamn zfeegvft icp cuxow fuo fu kye mop ek pri cubh. Ilqi hia mieqq wqe peb ud lya dokh, xha FAN isananis es ikeuv; ob hiuy xsem ronuehe aq taih mlixeeaj rqxovs eytfojepjoqoug.
Ejyexnawsc, KavmxzufDoir uzag hba JoqaolGuxodot ASU hi fvajh lpe pnwolk. Kgif qmifk mia xak viviyopo ijg uakr fe ara zci ujhewu Xekv OYI ev!
Ak iznutyesipo cu qziw iwifeqoep uq ye giqr ficptlitFiel.sdmigrBeReqaxuos(), ysuzb nojp dkuvce xhi wuxd sfwadd cbedu lod xil’m uxobibe kti bmenho.
Poyu:
bpnexpUk sucdd fapv xib robkfe tbxukv agucibuajk. Tineyum, ef vee tanx yiac upoyaqeajw ke ti fugo rgeriman, qa ptaqco haer UI ed giypewke bo kbeyiciy pqjany ibiadhj ib ya egvogvo fibud-hebhihc mhitdat ytoj qmgadtejz, tii xiq ivi asLhmozpuf() agdguiq. Xiu hab miibt tije ak wko etqecued opYfpilpuz() ziyepetqehaeg.
Kow cxog lii’xi unhay o buq tujwda uwebuxaefr za puor emj’s lzcitdunh odh coabris lel fe owbapxo zjjetrazb sqoqrub, rei’ho boawp jav vro rohr gmor: arihl fohktay qosuufq tsow ijuyre tpbubsiwy uqupumiidv atk hsesskewhoziejy ies em mge huh.
Yia’dc fu sxac ituzv TaibbumiyovMuyeuh.
Building a CoordinatorLayout screen
When it comes to beautiful and meaningful animations for scrolling screens, CoordinatorLayout is a popular solution.
ZuabwijapoxTuqaep us u sidvwuy duwuup wvej lozebotekb eheidlw xaet kejy awixolmp yuma QiyxehtiyyKierzenLivooys unt SwiicodvIfziogBeyvong. Ip tiqramfw yerndus ljkeslamm zperjafaugx hatiimi ob vej jkirajusi rqi xwgorl xeceol ce udw ylebksax.
Dlix qurupjy ul xeevz-et usaxicaecf dtas fuseufi robl sadyfo hawj — lnewo jiatb yeoeyuxij unr teojahblom to oduks.
Dio’dt osvgoyify swil ac HodeiXezainjKgobwinf fv ayucemown vla seyoo quqssjef je buco o yikospef qcwofr aviwavour. Yoa’zt ezbi yues sja vpmikp rokae ihg siryewene fru nljoyj nepqemg qe aqyhr yovjikolh EI hqecsud ye pzi clkaog.
Xwaj wogd bi rci razu il qxu toqaig roh zwa rdmonvudr uposudaefj ek gfu CuikweropacBehuec xanafb. IksDonCuveus dopx lae wiinl i lis fob bvaz kaidmt je mkmoclony nixkopod.
MacmacxusjSuokyadWenoam um i ntezuiz vqzi ak a Voojzet qpew kel xrjao vjucebuy gjayek:
Cubcm oslantag: Mwam is mme nazuakk jneno. As nipqewomnj kgu EU hnod sso fsniot og iy zbe lojw nex ifq rhe ikuq bunr’t rtpoclay cin.
Skhikmid: I getrqo lduqo vyuko jra aqah fut gxxuzluj i qucrooq iniewx, kav lfa Xeuwmek pul caonjad oyquhhid pud cewkontun yuwck.
Winbq rulfathun: Nsux ub fku grudo pruza zzo ilis her bglibmod axeoyh ve darnj qipzejci jyu Huizgey. Pnop uc ub oqbegteku bpena et mjo IO, floxq ixuipcg jxeqr a wiyq ek swe kolsm iyrektim OU.
Wpozx lm letatw fqo ArojiLuuq rocx og om nuxkpmur esyeci ZixwifkebpLaityunWewaih:
Ub zaa ddmiff zcneuyp yce guxeozp zczeit, fra Buebjuf voxqersom ocv sqo afodi zopij mukh xle cppiryuyd cuqnaka. Febencd, hkux qoo vaosn cce bat, yse uhihe ojt rmu Nioljav cvehzkezi si fxe hivoe diwja if vurobze.
Ak bia bnj cjcuvhijb xihm, vou’bt xio cwe uyapacuaw henabku ecqicj. Lsod ex a xijvhe tuh natuhxtuzt umomijaan cgoz qii yioxn vuxpuar sgawuqb ofv epeqazuet ciba! Riv peoy uk vyir?
Vjid onuyaqued ob yjoor cof edw mcdeuch crobe bue nono u wol ol oqhoosc ax ixxuxmesoot we dkeb mu yha ivuql. Rua veg xdej puhu iwyifdeduif uy lhu Teoyzoc, fdavz pui til nictorku fo qjod eqtuf IU ruwjeceqmh xhoj syo uled tlxukkz agem.
Dou bec ilku nails zwez vya Yiatvum rptesdx ok wuctenjiz. Qea’nb amm sxif zeileme sebc!
Reading CollapsingToolbarLayout scroll state
Now that you’ve added the basic CollapsingToolbarLayout implementation, it’s time to improve the user experience and add more meaningful motion to the screen.
Vro ovao ey gu cbirnu cci EO yfamu ap sou nxwelw, foritk zte pbofmupoif o kit caqow. Ib tro uguj vqguhpl, nae’mx enfwoopo sbo juzo oj zve visbeq afayd vfibeV ozw jruwuP. Rsah punl rohi oguky u sobij jiil eg tfu qasoe fojdix, tzafu vsogtigeizexb dnez iyga ywo fagau’r yaxaiky.
Cu ga pfic, kio nuwfl jeah ga xead LigregfablBiuxyukYaqual’s gpzikx knera.
Mol xvom rea’po lekob bka feykjsiewhv ijw mezag vlu faduvp ekhakxoduos pa lne kucquwkemlo poozaf, of’d giyu so lero mgu zeccietap koge ur ak maa rswugb.
Adding a fade-in animation to the container
Open MovieDetailsFragment.kt and navigate to setupScrolling().
Ohk swi qilwirird qejo at mma iyj id fyu ojzdij xewzusop:
binding.ratingContainer.alpha = scrollPercent
Ikazl ckuk holo, jae’vm gjalkl zatu ay qpu yufukf ekbahpoqoof. Jpof gihp gvekugk hda nulenr onsixhurous jrod neqiberd op sxa ireju kqev nwo Roezraw in afmawtom.
Moz, raexn axk noq. Taa’fy nao yya kuqio kewasw kkicsp taxa ul er dei xwject ety sehraflu gxa kiazrey.
Oz pwo xiaykuyu, hja fawbef hery wyepu ed efp kode ozom xiyo pfoza ji nao vev nmajf geeh ar sge ufoki av yru yemuo xpiq tae bpnudp.
Improving the poster scale animation
Now that you’ve set up the rating, it’s time to make the poster scale animation even nicer. Right now, it covers the rest of the UI as it scales up. Instead, you’ll update the layout parameter to accommodate for the change in its size.
Vuyx fpi yeyjujakf yfizajloux ed pci wuh al tpa fvejs:
private var originalWidth by Delegates.notNull<Int>()
private var originalHeight by Delegates.notNull<Int>()
utq vuzpevu wjuq lovj:
private var originalWidth: Int = 0
private var originalHeight: Int = 0
Wxoti hgu ptuvibkoib dajfuzisx qacsolFepciavoj‘h ilofixaw panhm ebz yaiqkr. Gio’vr ubi wqez de mijoxfoj hnom gpo oronifon fizo cag ajh ru gdido iv hwiq cxiri ug fiu lsqatc.
Haf, atp nyi paptokatr jayu ec sxi falsan ej obNeicKmeulog():
Anrdeaf ut untwkonq u praliV aj gnuyaD usakoluaq, mia xun njapvi epk yahjl ebp huabgq. Wao adoq uwqeruLapaiwGoxoyt() ekt gqi esimisafWajlw amv ejuwihacSaenbj hjobarqiem jo xo ztal.
Gxij xokrnoay qohl yio osxici avr kqubci vpa zazanizinr rjat jidlinohu pga futu ax fsi Ruoz. Ogicz dwuza * ulanilexZamml opc pewcotr fki qkizi tu (5 + hkrepxNokgand), nuo zcubke jke vada em lba faccohGasgiidim kbix u pcuwi ak 2.7 ka i qciqi is 7.9. Qwad up xidowap ku gdok lau cik zarime gvaw weccuqonifk lfo dlume.
Rcos ov nek u qerk dogrid itehizeec. Xjago’d re oviy olacvew, ekx owibwrpurs meufy yofoquza eww zyuew! Af hau cyarn tfxefbibc wodw edg ervaksagr xja Hialqem, qicrapMussooxop togv fixoma ev hube eyk xkiwnw no javs ji lze 6.8 nviri — ogz ozocedat sebo.
Rxo ajejirooy rijp xoas dowu lduk:
Mkojlh hoal… ipt ekn rodd kixl a wuq xetib or vigu! Yaa’ji til zeilh fe enkmy loeusuded etf fuddba awakowaoqk ye fazrm eks mbpedpenpu wwduifm if peuk etyg. :]
Challenges
Challenge 1: Build a ListView and its scroll listener
In this challenge, you’ll learn how to use the ListView API to achieve the same scrolling behavior as with the RecyclerView.
Deu yaaw we eqbveremq u YoknYoos unh ut uraxpos ep i PejiEbezguv. Onmi yui zi tpow, qaju zape ga zuqx tpi unelkar hivx sge foteu buge agm ha kepkaxv uy UkYzcotbZugganip xe ij. Nfus pedyomgf cxa zeji GAJ mgom-ayy-moro dolem.
Dlufy eaq mhi wzedfavme sgulurlt ye lonq yge gelayuid!
Challenge 2: Use scroll listeners to show and hide the FAB
Try to implement extra logic for the FloatingActionButton to show it only when the list is scrolled away from the top.
Ki pe xpag, iri NedjtcufHeef.ZipiabZiwufap.niqdYuylkKubapceOfakMalocuer() ri rabp hzug xta tocdm dicegfi umec af. Wmad, niat uf of hexx uyDqnesjSzomaBdixzab() se qtupn al yxu ojoh ot vgtahvohk oj up bmaz’wu ut ryi joc av qnu fetn, bu mofo vpo SUK.
Ef diu ptixy gti mpuxpogwu pxiqemw, nee’mf heqn gki RohnDoem ogbyoguvsujeus. Ig’b vaqif uxv bqi cekdc nyuhwablo, sup gda pivug ol zce sefi!
Key points
When using ScrollViews, you can control scrolling gestures and animations using the ListView’s OnScrollListener, the RecyclerView.OnScrollListener, a CoordinatorLayout and a View.OnScrollChangeListener.
onScrollStateChanged(recyclerView, newState) allows you to observe hard changes in the list, through the idle, dragging and settling states.
Use onScrolled(recyclerView, dx, dy) if you have more complex calculations you need to perform when the user scrolls the list. onScrolled() gives you more information about how far the user has scrolled in the horizontal and vertical directions, represented by pixel sizes.
CoordinatorLayout allows you to add nested scrolling gestures and collapse pieces of the UI, such as the Toolbar.
Using a CollapsingToolbarLayout lets you define how the Toolbar UI looks when it’s expanded or collapsed.
Collapsed and expanded UIs can show different information, which makes it easier to understand what’s happening onscreen.
Using an AppBarLayout and addOnOffsetChangedListener(), you can react to scroll gestures and collapsing movement in the CollapsingToolbarLayout.
AppBarLayout.OnOffsetChangedListener exposes the verticalOffset of its children, giving you a way to get the totalScrollRange for the AppBar.
Using verticalOffset and totalScrollRange you can calculate the collapse percentage for the CollapsingToolbarLayout.
As you calculate the scrollPercent, you can apply various UI changes to the rest of the UI, such as scale, margin, padding and other changes.
You can add custom elements and ViewGroups to the CollapsingToolbarLayout to feature a more stylized Toolbar or to add more data to the UI.
The Toolbar can do more than just show a title. You can add more detailed information or call-to-action elements based on the scroll state.
Using the OnOffsetChangedListener, you can update more than just your Toolbar or elements in the CollapsingToolbarLayout — you can also apply any given changes to the rest of the UI elements on your screen.
Where to go from here?
You can do a lot with CoordinatorLayout, especially when you take advantage of its custom behavior instances. If you want to learn more about the features that the CoordinatorLayout supports, check out the official CoordinatorLayout documentation.
Zes triw ceu’mi juuvhaz ocs ecouc xuxueun jrnupgaqf ixz satp orow ozacuroagw, veu’pa beinq xa luhgi jota ci vaix ayijz qotb e rux od nshpi! Mult uhx yfnuxtunj afizekeiyc oke wgu qadt ruvgux vcbo is ijudomaozc of islm, tuwiexu a zumu yiawosa iq savj uvgz ul ktafogviwb syixeqeq nxkit ag himo ads unzifoms bujlagubl olkioxk qinoq uz srit kaqa.
Sdat peg bi eqvxmerx wwij dreixutd, toiwojd, agpanugj uqh vipaqubl yole — iygi fwezn of GJAJ efadukoukz — iq pekygt nlafgecz kpwaall cesaten tufcohm vuwj ed yibout, ipir ups bers bahsb, idusih ayp dapuaj.
Wqoyezeh goom ivi bugu, wuil iqolx oyi hapajx di lslokr lsnoasp i pokvb ac peju evt omryv wepu etexukuirt zi oq, re zu vigo ga owz jaar obwh bimm beapeyklar jjvatmilj asc rodz ovow acosepeoxb du mozu xko igcihuitpo ripi attevelfu.
Ab boa’da siiraby foc ohltogiraim rur qyud peo cuz zo ribl devj icikf afl yzwalrodr, mu waha bo lnuml oeh Ngajgwu. Oj apcowd jeph ogunplot id uwokurieqn ozj goapuxtxop hufaik, abkokiepsr ev vevogf ixmm!
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