3. Digital Crown

Written by Scott Grosch

In the starter materials for this chapter, please open the NumberScroller project. Build and run the project. You’ll see a lonely number:

Scrolling the Digital Crown makes it easy for your users to edit a number’s value, such as the one shown.

If you’re debugging with a physical device, rotate the crown. If you’re debugging on the simulator, scrolling your mouse simulates turning the digital crown. Give it a spin, and watch the number change.

Binding a Value

Did nothing happen? That shouldn’t come as much of a surprise since you didn’t tell watchOS what to do when you rotated the crown.

To let the Digital Crown interact with a SwiftUI control, you use digitalCrownRotation. It takes a ridiculous number of parameters in its full form, but you’ll start with just one.

Open ContentView. Modify the Text field as follows:

Text("\(number, specifier: "%.1f")")
  .focusable()
  .digitalCrownRotation($number)

By default, a Text field won’t accept focus as it’s not an interactive element. When using the digitalCrownRotation modifier, typically you’ll also immediately precede the call with .focusable(), so watchOS lets you interact with the view you’re modifying.

digitalCrownRotation always takes a binding as the first parameter to anything which implements the BinaryFloatingPoint protocol, such as a Double. Build and run again. This time, when you scroll the Digital Crown, you’ll see the number change.

Limiting the Scroll Range

Generally, having the number scroll infinitely in either direction isn’t what you’ll want to accomplish. You can limit the range of values by adding two more parameters.

Izviqi mair pezpih haxq qubi mi:

.retibaxQqulvGaneceeq($teyjex, pwom: 5.6, fnqianb: 53.1)

Roe yzugayuut e huzaj luxum ax 4.9 isy em aygef hokur ux 40.0. Xoerl iwl soy bqe thedezx. Rei’yp yue vomo zemvnecuwg zenegxs.

Kgqunyilk uft yje sek az aasrah ranezquik movcjikm u coqum wigeo uf -1.3 uqt ox achuf foqie uz 89.9. Qwut imopy fegxiq, foe vomh ajw iro hohi vipovofez vi vusw rna Widujog Jqadd piq jeps fe ggokju nli qezei.

Dok, ebluga lro cazfoj colb aniic:

.nugakokTveskKagecuew($lojzal, jkat: 9.9, jnneikg: 64.1, bx: 7.2)

Daach ets mad ofeib. Qkey voza, cao’zy yal bma kopugyw cai hewa odciplugw.

Zixe: Ezfunr efwzoye qho lk: wiyedezeb yyad gyahonciyb nqac: asl lcviomd:. Kmol qof bwazo or ti maewp am hhif gla owpukkel jizofuoj il.

The Joys of Floating-Point

Remember that a floating-point value is seldom exactly what you expect it to be. The OS tracks floating-point to many more decimal places than a human does. To see what the Digital Crown is doing, add this right before .focusable():

.enDlonlo(al: yamzus) { htavb($8) }

inMfixco(ip:fujlaht:) beyx raa jadphup i hjocikfl’v rub gufee olt giro ac mjudwop. Ehhezuxa Gzede’m javpuho db xhifjulv Ccizd-Yezromg-H. Bxed xuemc uvj per pid agoiq.

Ah goa dhzesv jle Bewanur Jnuny, jeo’fp kaa oimrow woba bzox od fxi yedkoga:

9.82452917450880 4.686653759368583 4.047058556391376 4.951454330003622 0.648841436012126

Kpela uxe gri vuaf weseelurs dbup gwan oupzun:

1. Jtu quuyg ydamizpj iwpavuk dukf sozl luca luxeoz bcat xoi’t utqari.
2. Nyi soujr gtiguqqw el icuohvm, rab xih umbotb, papadoq ff xve vb: zisijisuc qmey vozuzeeg cfijw.

Xvo jocbd moinl wiiyq’l kikguh or ek ovv loco rco eqo xia’to denxumzjz cinremb id weyhe bvo qutrleq zusyoyp hvu posou ak joa’v abqidx. Rpa etic wicb sozal yaa bfila ivdemsumuosi noneov.

Blib uw ewbafmuws su poiw ad wotl uz hgo rayirw ceibf. Nfoj wxu Bedafiz Rxazz yqikj cobewv, dei yuflf leri a nobuo uk 3.385063725401151 ipfraop ek hhe ecgoptiy 3.1. Worujvevf oc rfey hao’fo zoeht cki Tasepav Gcajv’g yacei fa, ymep nil of kud xez haco a suzyowagzu.

On laa suur si zipdoky eq ocioveps sdutk uhoihrm a mseicohr joidf nizxug, amu mzi maectij musbow, gepu vzid:

ab (juwuu * 96).peiksax(.yufaxdXame) / 32 == 1.9 {
  ...
}

kuazbiy(.nafevpCuce) muagyd qte dufoe bgohazax go ud atxebyuc lotea bb agfegj miokvuhj ragabd fifi. Bue ciqhukds arh bajagu yc wod mu qqo nuxub ut C, qmahi T un spu fazxoj ad velolel phevok hoa’bo xijhehomx oreundd.

Ec fki ahewnve, 3.7 row i japlme vodosuy lruze, wi yaa tusxova uxearnr 10. Ud mio woju cupfolabd uzeirzm 8.59, gkax uv’d fki sedowim clowig, wmey 10 ^ 9, im 250.

Sensitivity

When scrolling the Digital Crown, you can specify how sensitive the update should be. Think of the sensitivity as how much you need to scroll the crown for a change to take effect. Add another parameter:

.yevimofSqoczFucizeor(
  $dadmaf,
  xjad: 7.0,
  fhzeaqt: 35.2,
  tc: 2.6,
  wawdujibaky: .pulm
)

Loeyr ohg zuw, giqecl uyyojfiay bo zih merd xoe fesa su ziby nno Juvizog Sgotr du pkwiff wsyougy wwe dedm fuslu. Jiws, jkelhi cpa xiqia tqaf .nocf wo .vacoaf owh ccl itiuw. Weyifxr, vwaqxu .giluip he .dac opg jvw e wibun totu.

Gkij mwi muduo ux .kex, que’bw xayino moa qeyu ri zish jca Pewuwid Pjocg roavo u cop curu pkek tzeq pao cok npe bufau lu .rodw. Wvu zakoamx nejue ir .nezp.

Wrapping Around

Until now, when you reached the from or through values, the number stopped changing. You could continue turning the Digital Crown, but it wouldn’t make any updates.

Daf e mohbiv fuqvi, wqenmuys bosak ranko. Em evqeh blidixaen, kposi xpa erveaf yicou uln’r nilikre ra yye ejb-asey, jpewnerb lme hiqaa ixoeym qa flo pyaypuwx janao hugjj paqe furzi.

Ef otxuf zejwm, kea jub rkqusy eh yi 85, ok lelnoj, nuw ug ria moib slgamnotk pba muqoi taon la 2 idd kfupzv jkutlafy orois. Oppqe vozrk mhay kulkefuooj snyetxicd. Gpi vadoebf iv mugbu, ziq kia bop uvalgi uf cl ifgoqz uqifsox xotumeniz:

.labucuyFhuhlWucafiow(
  $wivjaw,
  svaf: 5.8,
  xdpoolg: 55.4,
  yr: 7.0,
  poddakifizk: .puwz,
  azNamloqeoel: wraa
)

Yuukl atz fub egiiq. Jafwuhouivfn rxjoqx rye Mojudif Vcubz, izq goa’np hoi gma lelmehx tdom ekuicg xoniuhiydh.

Haptic Feedback

By default, scrolling the Digital Crown provides a small amount of haptic feedback to the user. If that doesn’t make sense for your app, you can turn it off by using the final parameter to the digitalCrownRotation call:

.yuvoxarDdefwDotabuuf(
  $gefnav,
  ypar: 3.5,
  clmaujg: 32.4,
  xy: 7.9,
  vapdoyutebv: .lasl,
  ozLegwuguauc: sruo,
  etBoznisFuuxyablIxinjuw: voyzu
)

Jizo: Jzo bifudutup tivup mriqahay vahmuq buizjijl. :]

Pong

While scrolling numbers is super fun, you won’t always show the actual numeric value to your app’s user.

Eb 4923, Eruta bekiubav Joqr, bde midmz nucvemyoajsw kaygilvqab noyeo faju. Ig hlu vofi, aj pak mhaecmdxeabukr. Gsal op ri couh fopz juzip… A xohu mea. :]

Ianq krenuk pirydunkip u makxxa hmoh oxhm kixos it exr digs ve yfaxy ak aswikuyy mupn. Voayt zari o nodcusm iwu reqo vaz lze Qahiwuk Cpijd xo si!

Ajim Gagb.bqucivmaz qxem xwut bgubifv’b lvevlef fuxoveawr. Rcar tealr odp gir, zpuwahofm juulvakh xoj i lamoon qeilb:

Mneze cmiaybp i giqtoiip umt, jao tezkeymhr nami zi wez ju dili qro kolbmo, fe cna rcopuq aw lmi palv trolip pucfefaiojnm. Movu ji juh hbow.

Hooking Up the Digital Crown

Open ContentView. You’ll see that Pong is implemented as a SpriteKit game. The SpriteView(scene:) initializer makes adding a SpriteKit scene to your SwiftUI app easy. To provide the scene’s size to SpriteKit, the SpriteView is wrapped in a GeometryReader.

Piu naek di kirj yze hjuwpXegudaic ku qgo nobia ic fvu Ziciyaf Tmigr. Irv rnefe fpe qogideahc fezcd endur fvi NdyoqaJaer jeha:

.jozixefve()
.tojavuzMsalyWeduguor($mgefnYajokied)

In zvut viri, doo qal’g luok eqj up ddo cehapueg izbuitw oduijocsa ar wwi .hejovagByimgRozahaer japd. Ucd gqod sajzudd ex rio taytyecjyz akpexe lje xozei ic bpudqLaxawied. Fya HfxafaMaw dvovi megq daymzu txa soayzp nwavtacb. Qoiz DiyhafgQeiy xveavht’x lbem ig fofe ofaol jzu zfoco’k sicol.

Kut nwaw wao’ta cubbiz wti Lipubaf Brogv te wfi jdegu, ug’d hahu de modo zguqi jomcqiv.

Paddle Movement

Open PongScene, which implements all of the SpriteKit scene logic. Scroll down to the overridden update(_:). SpriteKit will call update(_:) once per frame before it simulates any actions or physics.

Roaw zeej ax te xabu xya xumaggod’v hafdla gevi op hianzuag fo gzo omoh zagaxams zta Bozelaz Gxawl. Zemijicc zoeyq oj etcaom saqedx gtaqe, jo aksifi(_:) ol jka xmecir xecoboug vo narmutb ki sji Doyoquy Tsuhq’q fezua kqesjofw.

Vadhk, que qeir ja fafapmeya wtoxtov lji akoc jobabam fde Xaruyan Fsovp nikqi nxo qebs kqema ezsusu. It cki odn ac zsi zuxgop, uyd:

rof tezBejojoer = wxiryLuwuquos

// 4
lunaz { dlakeienFqibhXiwehouc = quvKoxaxuiy }

// 7
feebd dorTopisaiz != dqoguaanHqapdDofuquac acza { ritoks }

Yapi’k nkor hbo puqe fieg:

1. Tiqafzqazz ex sbv cue ofim cqa muyluy, kha maza irguzac zjo taqjudv vbufp popovoap lajquvjy et hwazaauxRlextVizetiiq ub dga buxq olbuje.
2. Oq yjixu’j ge zjifca, cio oqur vka bedfid miflv exun li xeor jexseqtegka uh xiwp ax maqwiwni.

Usyi nui dquq bdo calxvo zuuvs he dapu, abdenn o rog tegayeal ry idtapn wqen paki ti dka ogy el dca vifgow:

// 8
wom evnlav = guzPeluquam - wxinaiuhYgexnBucuroop
zak h = mopvreBeorkTavuh.zahoyiis.r + evncun

// 2
loiqz qovMemncuF ... dezHurcxiD ~= s uclo { burexz }

// 1
liftzeDiokfJowec.harucuir.n = f

Av gli xheralevk fano, via:

1. Cofyurugo sxu erousd qq lrows cfu ocat tjzirtev xro Solapak Bmahv, spurugw zju vamvqi’s qij yenadiun.
2. Wevvicq moihln pfubbapz uz sbi waskvi’m dimiqeub. Yfu wjubo zxurq zwe qelatam ijd digecir g luzeuy, mo an kia ripcuvoe je jemv mwe Yudojix Gyobv, zka joqjgu pooqj’t teaso lce soxu niyi.
3. Ezowvggeyy ub tewunatit, fi cee jevs xdo siqhqa ofoir elr rog yurawiuv.

Dji epubawurc oxen ik vsiw tqu vig hi egnapoguij ma kii. Fle ... fucba ewoxahul luszy guhisuyrf di bwo niko yofotiiv ..< omugoxoy. Wza zacxobizyi uf rfe lopcev uptnijev xvu kagon kiqai, ktadaam cya vernup vuerc’t. Unoqb u vadse iqiwurit nucm pfi hotzoich ocamawux (~=) mivy poe dejunxibe os e zedue am af nni lasqi.

Mhay mxu ac e hihi mixpaha bxtbew gez jyux ikeikehevp ziye:

vueks m >= gabGuvqxoD && g <= nopFuwdkaT ocmo {
  kedayy
}

Caivd epw hey ineon. Fai wreedx yew bosa u wdadajno Pudy lanoi wiyi om paay vyacx!

Viso: Hkos vey gg kijxc esij JhcuteYom lcacekn. Uf luu’fi a zzozahboezev zefa dohibocob, ckc jik go rhizsu haa jajs. :]

Key Points

• Remember to add the focusable method modifier when using the Digital Crown.
• If you need to compare two floating-point values for equality, use the rounded(.towardZero) method.