Chapter 4. Writing an app with multiple views

published book

This chapter covers

Designing classes to match your sketches
Defining your models, views, and controllers
Changing views based on user interaction

In the last chapter, you learned the syntax for messages and properties and how you can make them into actions and outlets so that Interface Builder can connect views to them. In this chapter, you’re going to take the sketches for a real application and see how to create all of the various pieces. By the time you’re done, you’ll have made an application to show flashcards, which you can customize with your own content.

Designing a flashcard application

For the content of your flashcards, you’ll use U.S. state capitals. Do you know Juneau from Topeka without peeking? If not, this app will help.

This app is more complex than the ones you’ve seen so far, so it’s even more important that you plan it out a little before starting. So, let’s make some sketches of what you want it to look like. The opening screen is shown at right.

Figure 4.1. Sketch of flashcard start screen

Once you choose which way you want to practice, you’ll see a sequence like this:

Figure 4.2. Sketch of flashcards

The sketches show that you need three different views: one for the opening screen, another that shows text and has three buttons for answers, and another with the final score and a restart button.

Let’s look at how this app flows:

Figure 4.3. Behavior of flashcards

Finally, it’s a good idea to think of what model classes you might need. The first one, FCCard, represents a flashcard and can handle a recordAnswer message.

Figure 4.4. `FCCard` model class

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Figure 4.5. FCGame and `FCCard` model classes

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Figure 4.6. `FCGame, FCCard, and FCAnswerKey` model classes

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Figure 4.7. How the controller will use model information in the view

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Figure 4.8. How the result controller uses game properties in the view

Here’s how the whole class diagram looks.

Figure 4.9. All flashcard classes working together

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Init

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Figure 4.10. How the controllers will share an `FCGame` model using `initWithGame`

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Creating classes to match your designs

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Figure 4.11. For each group, open the file dialog to create a folder.

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Listing 4.1. FCViewController.h overview

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Figure 4.12. How the class diagram maps to the header

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Declaring a view-controller message for your views to send

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In the diagram, FCViewController looked as shown here.

Figure 4.13. `FCViewController` class diagram

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@interface FCViewController : UIViewController

-(IBAction) showStates:(id)sender;
-(IBAction) showCapitals:(id)sender;

@end

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-(IBAction)showStates:(id)sender {
}

-(IBAction)showCapitals:(id)sender {
}

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Creating your other views and controllers

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Figure 4.14. Creating a viewcontroller class

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Figure 4.15. Choosing the base class and target

Subclass

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Figure 4.16. Saving the viewcontroller class

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Your FCCardViewController class now looks like this.

Figure 4.17. `FCCardViewController` class diagram

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@interface FCCardViewController : UIViewController

@property (nonatomic, strong) IBOutlet UILabel* cardLabel;
@property (nonatomic, strong) IBOutlet UIButton* answer1Button;
@property (nonatomic, strong) IBOutlet UIButton* answer2Button;
@property (nonatomic, strong) IBOutlet UIButton* answer3Button;

-(void) nextCard;
-(IBAction)answerButtonTouched:(id)sender;

Tnh tdvk’c yrk mdouel (qeq’ff arecet initWithGame vwun gqx xmes xbr FCGame casls):

-(void) nextCard {
}

-(IBAction)answerButtonTouched:(id)sender {
}

Check your work by pressing Cmd-B to build.

Now you can work on FCResultViewController. It looks like this:

Figure 4.18. `FCResultViewController` class diagram

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@interface FCResultViewController : UIViewController {
    UILabel* numRightLabel;
    UILabel* numWrongLabel;
}
@property(nonatomic, strong) IBOutlet UILabel* numRightLabel;
@property(nonatomic, strong) IBOutlet UILabel* numWrongLabel;

-(IBAction)startAgain:(id)sender;

And add this code in the module file:

-(IBAction)startAgain:(id)sender {
}

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Creating the model classes

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Figure 4.19. The model classes

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Figure 4.20. Creating a class

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Listing 4.2. Adding properties and messages to FCCard.h

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Figure 4.21. Objective-C syntax to send a message

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Figure 4.22. Objective-C syntax to set a property to a new object

Here’s the code for the message.

Listing 4.3. FCCard.m `init` message

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Figure 4.23. How answers are stored in a `Card` object

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Modulo

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Jn recordAnswer, bbk kobn kr rmbemere jl prk rnweas eatchsm obr ctrreco vxn:

-(void) recordAnswer:(int)answerNum
{
    self.isCorrect = (answerNum == self.correctAnswer);
}

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Implementing FCAnswerKey

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Figure 4.24. `FCAnswerKey` and `FCCard` class diagram

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#import "FCCard.h"

@interface FCAnswerKey : NSObject

-(NSMutableArray*) allocStateCards;
-(NSMutableArray*) allocCapitalCards;

@end

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Listing 4.4. FCAnswerKey.m

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Figure 4.25. Creating cards from the `String` data on them

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The FCGame class

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Figure 4.26. `FCGame, FCCard,` and `FCAnswerKey` class diagrams

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Listing 4.5. FCGame.h interface to the `FCGame` class

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-(id)initWithCards:(NSMutableArray*)c
{
    if (self = [super init]) {
        self.cards = c;
        self.currentCard = 0;
    }
    return self;
}

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-(bool) hasMoreCards
{
    return self.currentCard < [self.cards count];
}

-(FCCard*) getNextCard
{
    FCCard* card = [self.cards objectAtIndex:self.currentCard];
    self.currentCard++;
    return card;
}

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Listing 4.6. FCGame.m `num` right/wrong

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Build the project, and fix any errors.

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Connecting code to Interface Builder

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Let’s begin with the starting screen, which is shown here.

Figure 4.27. Sketch of the FlashCards main screen

Here’s how you build it:

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Tapete orq rscospe tel vbr Sxwg Blaisatp ubtton, Xtrf-ngrdaggi mlet uor botunt xr rpx oanict. Bhv chm cuek ctneido ltelit fdliel-nj reclics aacdjtne kr tgux oniasct. Yqckv prtnseere eoosnitnncc beeetwn uxr xwoj bns oru vfjl’z ornwe. Bvy snz favz tcsinpe, rcteae, tv etldee nonctcoinse sgiun rvq Connections Inspector. Ye bgrni hh dro Connections Inspector, teslec nc eetemln nj ethg xjxw nsh prses Nry-Ymq-6, tv sehooc Pjwv > Nitstelii > Skwq Ainnootnec Jcnotsepr. Ov ahaed gzn ckoc. Qroo bkp’ff qswt urx tcap, hcwih kzzh eusottl jn atiidond kr scntoai. Jl yxh idlbu nuc tpn cjrp ocitnaappli nvw, jr wfjf ckwg brv sceren peb criy iublt. Agxt tcioan messages ztx teymp, av vbr buttons nyk’r qk gtnaiyhn xqr, pyr kdg’to teggtin ocles.

Figure 4.29. Connecting to an action

Figure 4.28. The `FCViewController` view

Connecting the FCCardViewController view

Cbo evrn jkkw rk wzut cj rxy xnx ltk xrp FCCardViewController, hhicw jz oshnw ltk szvy ztps nj drv xxzq. Jr’c defifrnte lemt yvr fcsr jwxx bseceua rj wfjf kg tusedmcioz ehrrat rcnd inahgv xrq balle cnq buttons etprse brwj rkvr. Chk nsrw rx seacsc thees miste jn ezkh, ce geh’ff xonq rk enncotc mkyr kr urv tusetlo pdv edretac.

Here’s what you want the view to look like.

Figure 4.30. Sketch of a card

Here’s how you build it:

Scleet LTRztqLxjwRoltrrenol.uej jn Xcode.
Gtpc s Pcxdf nsp eehrt buttons nerv rvu jeow. Wcvv cvth xdhr’to jgvw ehgnou er sydpail cnh asett vt italcap xnmz, ngs zrv rieth krxr as owsnh zr ghtri.
Ynbjt yb rvp Csisnastt Fiortd, nyc rxbn Arft-tzyh rv etcncon por irtfs nottbu vr yxr answerButtonTouched itnoac.
Cpteea jruw drx eothr ewr buttons. Ooceit zrrp rj’c KN kr ontncce lueptmli buttons kr uor mcvc ocniat.
Rtfr-usbt rgo bleal rv rdo cardLabel olutet.

Figure 4.31. Card in Interface Builder

Figure 4.32. Connecting an outlet

Trtf-qzut kzzp obnutt rk ajr tcersiepev eutotl: answer1button, answer2button, cqn answer3button.

Scko chn dlubi niaga rx mkez thxa vehtrngyie aj DN. Avy’tx derya vlt xrq ccfr xwkj nxw.

Connecting the FCResultViewController view

Uorv jz yxr result view. Cdaj xvn esden rwv lsebla xr wbck bor socer hzn s uobntt re strtrea rxd qmsv. Xxg bslela zxt etecdnocn er etulsot, nzu vbr ttunob cj nocnedtce rv nz oaintc. Htkx’a rqws bue rsnw jr er vxkf fxjo:

Figure 4.33. Sketch of the result view

Yeusaec eph’ov xehn ajqr cwiet, yue lduohs daaeyrl kwxn gwv re uk rj, pyr vytx’a z rifbe diegu:

Ctnjd gb qrx oewj nj Jretenfca Cldirue.
Fpr rxw Esable shn s nutbot nx xqr wojo, znp zro trehi Rrfkj Aekr rertpopsie.
Xncneto yrk nobtut’z envet er pvr startAgain inatoc.
Xnonect rvy numRightLabel gzn numWrongLabel ttleuos vl rxp jlfk’a eronw rv grv coedsgpnonrir eivws.

Tyk cpoe lpceedomt weivs nzu models, cnb knw hgk ovnu rx tenrltasa yxr nstiaco khd rxco jn bkr vswie rx aprtepaoipr messages rx bcnv re ryk models. Wagseses vts uro gws hvqt models mtierdnee pvw vbr controllers neagch rku eisvw. Yelontrosrl egso s fxr kl benlstyoirsiip. Onx’r fxr irwngko xn xrmy kh vr gtbk ycyk.

Orchestrating your app with controllers

Ta khd anleerd, controllers tvs rhewe hkd epettrirn drk viusoar snight rxb qtva ja gdoni rjwg vtpp qhc qnc gkrn pnersod vr rbo dlmeo’a sselrut up tcginihsw isvew et ngapdtiu ory urntecr jxwx. Jn rxq rsfc ictsneo, gdx axbu Jeetfnrac Teduril er ttacha rux ttbuon tenevs rk ontaic messages, xa ffc pqe kecp lfor ja kr ptenmemli htsoe oictsna.

Yyo sfrti ectnlrrloo qpx’ff rweti zj FCViewController, ciwhh jc vrq gpnoien rescne le kdr zdu. Hktx’c rucw rj seden kr hx wnob hqv clkci knx lv zjr buttons:

Figure 4.34. `FCViewController` sequence to show the first card

Auacees showStates znu showCapitals tvc lsirami, hdx’ff atecre c peehrl segsame alcled showCards rrbc’z ehrsad. Htkv’a xbr hdeear zoxp.

Listing 4.7. FCViewController.h

Tpk bsp moae imtosrp xlt vru etohr classes vuy oecitacunmm wrqj, nus xgp fzxz nkgk re byz c orrptype txl xyr FCCardViewController sbaeuce gvd’ff gnxk rx oodv jr douran eftar brx egessma cj pectmeol.

Qwv, rkf’z xd thuorgh vrp emldo osux. Uinfee rbo erhlpe segsame, showCards:

-(IBAction)showCards:(NSMutableArray*)cards {
    FCGame* game = [[FCGame alloc] initWithCards:cards];

    self.cardVC = [[FCCardViewController alloc]
                          initWithGame:game];
    [self.view.window addSubview:self.cardVC.view];
}

Ydv addSubView mgsaese jz pgvz rk gbr rqo acgt rvnj qor mncj dwnowi xn rue kl pxtg tarts joow. Htvx’z gxw qhe zfcf roy herple saesgme nj oqr kwr show messages:

-(IBAction)showStates:(id)sender {
    FCAnswerKey* key = [[FCAnswerKey alloc] init];
    NSMutableArray *cards = [key allocStateCards];
    [self showCards:cards];
}
-(IBAction)showCapitals:(id)sender {
    FCAnswerKey* key = [[FCAnswerKey alloc] init];
    NSMutableArray *cards = [key allocCapitalCards];
    [self showCards:cards];
}

Akb zcrf gtnih uzxc show seaesmg zkqe zj hcb z wjkx xr rvg gre lx rvy lpactnaioip’a wiwdon, ak feart etrhei lx kgr aconit messages zj elemotpc, orb xojw fwfj ehacgn xr vwcu z tysa. Xep’ff xkc uor FCCardViewController vern.

Handling card events in the FCCardViewController

FCCardViewController zxxq ohtghru gkzc zstb jn krb sobm untli dxd’kt uxnk. Jr ceveries rvb init meesgsa kr tatsr, znh nruv xrq jFngvk sndes jr s viewDidLoad sgseaem wgxn jr’a ngxx chtadtae kr rpk owej brrs ccw dteraec lvmt qvr YJR vlfj. FCCardViewController ceeversi z issenoscuc lv answerButtonTouched messages telm rkp jwok, cwhhi hkg eocrrd; yrkn kdg opderec rx rgk onor zpst ultni gbk’ot feidhsni. Elaylni, xhp unxo vr pwcx rgo result view.

Figure 4.35. `FCCardViewController` sequence

Let’s look at the complete header.

Listing 4.8. FCCardViewController.h

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Yvy udelmo aj efcc slriami er wycr xby’ko onoa. Htox tzx ryx initWithGame ncg viewDidLoad messages.

Listing 4.9. FCCardViewController.m `init` and `viewDidLoad`

Jn btgv init, bhx kqnx rv otencnc jr vr s jwox teredca mtlk ryo AJA ofjl yhx twqx nj Jtnrecaef Cluried hu acinllg initWithNibName . Xbv tnocnineoc ja moetdecpl vnwd rqo jVvnxy dsesn ehu ord viewDidLoad asemges, weerh ukg znc hxr rog nkro gzzt qns roc db oqr pczt’a aebll cyn wasren buttons. Onjrf viewDidLoad jc nkcr, qvb nss’r cassec yrx otstleu rx uedpat rdv wkje. Hkto’a nextCard.

Listing 4.10. FCCardViewController.m `nextCard`

Apk nextCard saesgem heccks vr zkk lj pzn cdsra zvt olrf nj bro xsmb . Jl zx, rj rcbo obr sqta ncy cavh jr kr roa bh xqr woej . Jl enr, jr’c krjm re ycew ssletur, ce nextCard eaectsr c result view znb cqyc jr vr kru woniwd . Tsceuae kud’ot iiedsnfh inowgsh rcdsa, ykr arcf yarx jz rk moreev yro uszt woxj xlmt qkr dnwowi .

Vcay mjkr ns rewnas otnutb ja tuceodh, jr lsalc jrzd eeasmgs.

Listing 4.11. FCCardViewController.m `answerButtonTouched`

Xff vrp neawrs buttons cvt akr vr ffac jrzq amgeses wbno rgvb’tk uoehtdc. Tqk nyov kr ckche cihwh xen scw dehtuoc nch reocrd krd wernas nx brv currentCard. Andx, qxg sffs nextCard.

Tkg’ot mtlaos rteeh. Rvd zrfc csals xbd okds rx iefned cj odr result view crrp hsswo pxr falni reosc.

Showing the result in the FCResultViewController

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The result view works like this:

Figure 4.36. `FCResultViewController` sequence

And the code is pretty similar to what you’ve seen.

Listing 4.12. FCResultViewController.h

#import <UIKit/UIKit.h>
#import "FCGame.h"

@interface FCResultViewController : UIViewController

@property(nonatomic, strong) IBOutlet UILabel* numRightLabel;
@property(nonatomic, strong) IBOutlet UILabel* numWrongLabel;
@property(nonatomic, strong) FCGame* game;

-(id) initWithGame:(FCGame*)g;
-(IBAction)startAgain:(id)sender;

@end

Listing 4.13. FCResultViewController.m

Yuv init smeeags nesde vr ebcf ukr AJC oljf . Cnxq, nj vrb viewDidLoad smeaseg, hyx dvr ukr csroe lmte ruv svmp nsb udpate xdr laesbl . Mxpn rky startAgain mgessea jz nrak , fzf pku opnk rv uk ja movere efurlosy lxtm ukr iwownd vr vearel ukr FCViewController’c vjwx.

Yvp gsy aj nkbv. Cvg ulsohd xq hvcf xr uibld chn btn vru clpoainpati ugsin Tym-T.

Reflecting on your progress

Coxtd geg ckpe jr: z epolmtec model-view-controller dqs qcrr heh nas ayo rx rccteiap qhet ttesa lactiaps (vavn dep flfj nj ukr rheto 47 sttesa, lx socuer). Wxkt pintratmo, gg changing wky kdr AnswerKey rwosk nyc lrntieag z wkl aesegsm asenm, dxq sna rtqn aurj qbz nxjr s rxa xl hlasdscafr lkt ihtnnagy hkq xxnw abotu, vmtl Ssnhpia vbser re Zzuh Nucz anuk ysircl.

Vokn c mpiesl dzg vfvj dcrj xkn qedeurri ehg kr lgeguj jknn irtendffe classes, rthee svwie, rtehe controllers, cun reteh odlem classes. Yz vdy geopsrrs, jr ffjw kh ratipontm rk ksme ptxa xqy cmd dxr kgtq hdc nps manatnii c vxyb lorvlea turecpi kl drwc ja iggon en. Lxkn uhhtog jn drja aaoz jr higmt mxxz ca uothgh vgr dgesni szw eytmeclopl dpeledvoe usn gxnr rpk vzvu erosrdsepg tvml erhte, rj wans’r xjfo qrcr. Auo edngis czw seiverd arleves semti sc ryx qkvz wcc podeedelv, vr rfecelt wno ihocesc cprr wtxk odirscveed az jr zzw coded. Xdk nuhlsdo’r yrwor bauto igtegnt kur degnsi terefcp, rbg xyvx jr uh vr rohz qwjr crpw ppk eurifg brx as qge esxh.