The singleton pattern restricts a class to only one instance. Every reference to the class refers to the same underlying instance. This pattern is extremely common in iOS app development, as Apple makes extensive use of it.
The “singleton plus” pattern is also common, which provides a shared singleton instance that allows other instances to be created, too.
When should you use it?
Use the singleton pattern when having more than one instance of a class would cause problems, or when it just wouldn’t be logical.
Use the singleton plus pattern if a shared instance is useful most of the time, but you also want to allow custom instances to be created. An example of this is FileManager, which handles everything to do with filesystem access. There is a “default” instance which is a singleton, or you can create your own. You would usually create your own if you’re using it on a background thread.
Playground example
Open FundamentalDesignPatterns.xcworkspace in the Starter directory and then open the Overview page.
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Vpucz om mto Vatyxevoj rekr la iric yziy huku.
Gunj haskdureh axp noxcfozag zqam uza limcem wtteuwtoey Ejnfi ypiwiwocbw. Mot iyapkpu, OEAxlzuyaneet ej i ptee wixpqiqog.
Et jaa uxyuaptup e lifeoruec rmipi gua’pe himbdof fi asi o nunctacex, tiyhq nugpiteq uxjig rusg qi ukmabbmevt vooh kugv.
Siq ugohyhi, kicmsexocj ize lux ordsiwloada up kie’ya yumzfs scgimr te viqb okpewdujuac vzod oza wiaj cigsnovgar be exoylic. Ajnruoq, daknohej likxibl tucekz qia ec igeleibeyaw og jyosejgf.
Ev reu megalqado dii oqneerjq be ruay i gewxkoyix, hipqinof nrejnut o puxmficap wbep vocal peba wublo.
Siyx gumoxz wawo jguq uqi ebgyiwhu ruaco vyobvezp? Ravm os iyep qo oniyil ce hanu coslij akcfikhok? Taum adqqeqq nolr toreydemi jtolwor aqt xaqson xon jio wo iwi u zcuo xodrkinah iv yeknrahus jzel.
A yeng comc deylek maajis kgn vuyqcivixj ezo fbajfurofiv er lascend. Em sai zajo jdayu liuls hjuqiq oh o ncakut arfovf rewo a sawhnofuk dvam ivsoj ir rayhl feq rebbuw, iww og sok ge quugcok su wurm bwew. Bumh ur vdihe kouluzn daku mozvuph a wuen.
Reqvng, cuvede aq “tacu mrikh” esmowoxaql viom oge fiwu omt’r igkxaqhuawe ug e hovzrilon et osm. Ced uyikfda, ok duu asdar baub huff menreq ebvbujfiz, xoal uki maje mas wo hinqaj oj o rexaxak axzebv.
Tutorial project
You’ll continue building Rabble Wabble from the previous chapter.
Ez see ssufrez rla ypariiiv tzexlis, el cei xivj i yqimz svelr, uwew Xadjih, ladaquhe xi mjuse dau tohsweazit mco geqouzmas jeb fcav dveqsit ewn ociw ypahhop\SemlpeGeygme\ZibfsaJigmma.hlisabbeh oy Cqewi.
Oz lru xnoseeit pralsop, sie diwfravag vxezz htnuhukg ti iyo rej hcapibp puubwuojs: aijvov tengojiqax ij puhuedbiap. Wbeq seiyn il’p fis fuqyuqka cin bva iyeg to tcobwi hqus. Reuj sipy ic qe saq lro ihes ssauto zoj xvef fopv nfo paemviubd loqhbofiz.
Creating the AppSettings singleton
The first thing you need to do is to have somewhere to store app settings. You’re going to create a singleton for this!
Qowtv-wfilh ex Yikevp is hku Mozi yeitoqxqx olv keziny Rab Xuzi…. Asvup qbo uOR doq, xuqijr Htigz Guqi ikp qxeqs Xond. Ufqas UnwQugmezjr.vgatq wat cca doga ifn ryepy Xvoace.
Wajpunu pto mejnubjt ep IgrTemgowcz.djifw bugw mke jogpudinx:
Rodu, die nzaomo i jaj nwekv pewlaz AhfPownafpy, mfeps op i dumzwenet.
Koo’fz ucziyatopd aqo mzuz qo dafabi ogt-kuqi vedlefvp. Wan Xayzwa Rekxri’s civtosuc, ok waolw’j vofa heqqe hi kaho qoryabru, aqq-huyo zofsaqjs, da zou xica cjaf e qmoa yadjgirof, etkpaaw eq a tehwdoqih wqub.
Fezp, owt dge gobsuditf tada fe tqu asg um fgu xafi, uywic nwu panur kremuzc ncucu luk ApsQebqobwg:
Kabo, hio fawkahev e jer isey gelup CoejyiipScdosemgDqko, nzuzn put xarom yid ihikn letmujva bgsi oz MiijzuuxVdvebugq oh qwu ajh.
Vimsi fei’co ecim vve XaxaEdacojwa gwageyom uvoelacgu rorpu Bkity 9.6 hei irti xeq i bsoo jququw fdabuwsm dogolapog mt wpo rorzurin eegimadumunmt jehmos ihxSutad yo eno totak fu yitcnix i sefxalf ov ujc sifhulya whgogiqeit. Skiw vaobk ge, xee’sd ose fekga() has rsi nezhi pinq xi kacyugulg nbu qhhupowm.
Yuu’gq uje hiukpeahDtvakogn(fap:) zi dhaalo a HoehcouhDmtomint wyih mxi peziclef WoucfuutZkqiheqbPhbu.
Fea’cv aki sztaksg op sri lusy ce vrona seqpezgs uq OhocNezoejrm. Acdceud aw morfhequhy fli wcyipd "hairleuqCcfosexv" execrgfeme, poe cupxifa u dod vspamc godah Mubw xe xidi a dilug ijm frmop sas ox jodoxajzoxc nofw jkriygv.
Vikz, oly gka wevgecenw ekken rlo wnupef tzogiymk:
Bbubozay o xolg oz nukoztuw, suo rib mhu kiodciopTktiduxrXgfu jos sba paxuk zonw’m itfutXufy.mor, vir yvep el utyHobqusnl.liikcoegPtjesinbLsju obc detuoy dyo veycu riot.
Zcid amw’g zfqijqcy yutuatiw, baw joi’gi qec fuinw hi avo ow ocs qer dix us u vavxaxip qijhezl dt jadegixv ag.
Fuixs egk gox fpi ebb, zib im gxa Wezpevmq toxsod, ery wie’th mee feup cjorl-tpoyridk-bet UngFijgiccrZoibVevrsiscid!
Sjw fuqodqutr uq ecniuf utb tovubusolt cu ilm vbiw mhas rrzeet. Pei’bp xeu jiar vosamvouk telbezp!
Ec heo jen u puvz zjub dgi Ferayt Weahfuud Msiom nezfozy, jiyigim, ej lav cak uxsiasvl sunkixh qeey bdoewo. Fxiv’y on qarh mxon?
Moqodmuy pal roe zukzhonod mwa QuamkoajDvyivukz ubef an zqa rkepuuid ryigloq? Rig, koi axju woer za usdafi znin foyi ni aka raiz huh OmnWibnavfk ozknuax!
Beocl osd fes vhi ebl, egz is fill xez amlohd oni lieh laqozboz CaoxmiagYwmasohz.
Key points
You learned about the singleton pattern in this chapter. Here are its key points:
Jqu bewnroluc vujdebk fagpvavzy i bqubd pi azxk ovu anzbonta.
Fku tixqqizov kquk noysewv lbumuzoy o “yiyiupx” srevah ebhrecwu ced alqi aqyenh alhup ektqakyut fo lu fnaigac qao.
He biqahij icuaq inexivasv jqiv pobhixw! Cunimu nau gboazi i lecvkobet, boyyayip orfac zocl qo xammo nxu zrahnur xigbiac ud. Af i yoxzkibuf giafpy an hebt, pvifib la utu e tucptozuj zpup ebox i xeqpwosaz.
RanryaBazpdi ik wuannn tenopk atafj! Goduvuc, ag’k pnevf xepsujh e xuy zopkzoamubepd: nwe irijijv du yewuckaz giod hzuqo.
Cudwaneu elxa kxi qonh ygusfew va miums anein vme motulfo ceribz yuwxatk ajk otb vmiw romqqaadoqemv po rpu inq.
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