ios programing

7/29/2019 ios programing

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Learn Objective CNguyn Giang [email protected]

092.881.3468


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Ngn ng lp trnh Objective C (ObjC) l mt ngn ng lp trnh da trn nn tng ngn ng C. Mi th lm vic trong C u lm vicObjC. ObjC thm vo nhiu tnh nng mi t C, thm lp trnh tng (Object-Oriented Programming, OOP) v Smalltalk message

Objective C l ngn ngc bin dch thnh m my (native maging vi C/C++, v do n nhanh hn so vi nhng ngn ng cho nh Java, Python hoc Ruby.

Mt khc, ObjC c nhiu tnh nng lm cho n linh ng hn C++. Obnh kiu tnh static typing v nh kiu ng dynamic typing, tubin c khai bo. Nhng v hiu nng lm vic th ObjC km hn C

Ngn ng Objective C c ra mt vo nm 1983 bi Brad Cox v To

Gii thiu


3/21

Trong Objective C khng s dng namespaces ging nh cc ngnthay vo phn bit cc class n t cc frameworks khc nhdng name prefixes tn ca class.

Cc tp tin c t chc bng cch tng t nh vi C/C++: tp tin ticha cc khai bo, tp tin m ngun (*.m) - thc hin vit cc dnkhai. (*.h) ngha l header, (*m) ngha l message hoc l methods

Chng trnh thc thi bt u vi hm int main(). c th s dng frameworks hoc cc class tnh ngha cn s d

#include.

Source Code


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Chng c v ging nhau, nhng khng phi l mt. Class l mttrong khi Object l mt th hin ca Class to. Class nh mt bntrong khi Objects l i tng tn ti thc s.

C php to ra mt class trong Objective C l rt n gin. N bphn:- Class interface thng c lu tr trong tp tin ClassName.h, ninstance variables v public method.

- M ngun thc thi c vit trong tp tin ClassName.m. Objective C s dng n k tha. Sau y l c php thng dng to ra class:

Class & Object


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Class Header (.h)

#import "AnyHeaderFile.h"@interface ClassName : SuperClass {

// declare instance variables

}

// define properties

// define methods (including any // custom initializers)

@end

Class Implementation (.m)

#import "YourClassName.h

@implementation ClassName

// synthesize properties

// implement methods (including any custom initializers, and dealloc)

@end

Class & Object


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Cch khi to Object (Class instance)://cch th nht:ClassName * myClass = [[ClassNamealloc] init];

//cch th hai:ClassName * myClass = [ClassNamenew];

//cch th ba:ClassName * myClass = [[ClassNamealloc] initWithSomething:someth

//myClass c s dng cho n khi gi release:[myClass release]; // khng cn thit vi ARC

Class & Object


7/21

Variable access (quyn truy cp) c thit lp bi cc t kho@private, @protected; cc t kho s dng c t trc nhm vthit lp. Thit lp mc nh l @protected.

truy cp instance variable s dng -> v d: person->name . Nu bn mun s dng static variable trong class, khi khai bo bn

kho static trong header file, bn ngoi vng ca @interface (vanytype staticVariable;).

Cch khai bo variables: anytype myVariable;@public

anytypeA myVariableA;

anytypeB myVariableB;

Variable & PropertVariable


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Trong @interface, khai bo nh sau @property anytype age;. Tngvic khai bo getter: (anytype) age; (trong ObjC getter khng c tin setter: (void) setAge: (anytype)age.

Trong @implementation, s dng @synthesize age;, tng ngcc lnh thc thi getter v setter mc nh. C th to ra cc lnh thccho getter v setter bng vic overide li setter v getter m khn@synthesize.

trnh nhm ln gia variable v property, cc property khng th s truy cp m s dng obj.age hoc [obj age].

Cc property c th c cc thuc tnh tu chn bng cch thm vo s@property, nh l: @property (readonly) anytype age; C th tm hi

thuc tnh t ti liu apple cung cp.

Variable & PropertProperty


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Cch nh ngha mt method:- (void)doIt; hoc - (anytype)doIt;+ (void)doIt; hoc + (anytype)doIt; //class method- (anytype)doItWithA:(anytype)a;

- (anytype)doItWithA:(anytype)a andB:(anytype)b;

Cch trin khai method:- (anytype)doItWithA:(anytype)a andB:(anytype)b {

// Do something with a and b... return retVal;

}

Method


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Mt iu khc bit v method trong Objective C l cc tham sc vi khi nim label, c s dng trong vic gi hm (vi Objectivehm c nh ngha l gi mt message ti object k tha t Sma

Label thc sc hnh thnh t tn y ca method. Bi vy mc label l doItWithA:andB:.

Method trong Objective C khng th overload bng kiu d liu ca thtrong cc ngn ng thng dng, nn khng th cng lc c

doIt(typeA) v doIt(typeB). Trong Objective C, khi gi mt message (gi mt method) khng tn t

a ra li lc bin dch, nhng sa ra exception trong lc thc thiv x l vi c php try...catch.

Method i khi c s dng vi khi nim l selector.

Method


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Trong ObjC, ngoi vic k tha t cc class, bn cng c th thm coclass hin c. C th pht trin cc class hin c m khng cn pcode trong class , tuy n khng mnh m nh Ruby (v d nh bthm cc instance varibale mi) nhng iu ny thc s rt tuyt vi.

y n c gi l category bi v nu c mt class nhiu metphn chia cc method ca n thnh nhiu loi v t chng trong cnhau.

Di y l cch khai bo mt category:@interface ExistingClass (SomeNewName)// methods

@end

Sau , include c header c v header mi vo ni bn mun s d c mt class vi cc method mi c thm vo.

Category


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ObjC c c hai kiu d liu l primitive v object. Vi kiu object chtr v khng c kiu gi tr.

Cc kiu d liu primitive (c bn): char, int, float, double, short, loObjC khng khuyn khch s dng cc kiu d liu primitive, c cc kv d nhNSInteger, NSUInteger, hoc CGFloat (y l cc phin trc an ton ca int, unsigned int, float). Ngoi ra cn c mt class ls dng cho vic boxing/unboxing kiu pimitive khi cn chuyn thnh

object. Kiu d liu logic c gi l BOOL, v gi tr khng ging nh c

khc True/False m ObjC s dng YES/NOJ.

Kiu Null gi l nil. i vi kiu con tr, nil c vit l Nil. TNSNumbercho int, class dng cho nil l NSNull.

Kiu chui trong ObjC l NSString.

Data types


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Cu trc ca lnh vng lp trong ObjC khng khc bit nhiu vi ckhc. ObjC c cc lnh lp for, while, do-while, for-each.

Sau y l c php ca cc vng lp:

for(; ; ) {

}

for(int i=0; i


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while () {

}

do {

} while ();

for( in ) {

}

Loopswhile (a


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ObjC c cc lnh iu kin: if, switch.

Sau y l c php ca cc lnh iu kin:

Conditions

if() {

}

switch () {

case :

break;

default:

break;

}

if(a


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Protocol nh ngha mt danh sch cc method bt buc hoc ty cclass chp nhn (adopt) protocol phi thc thi.

Cc method khai bo trong protocol cng c th l cc khai bo propkha @optional v @required th hin theo ng ngha ca n, ndng t kha th mc nh l @required.

Protocol c s dng trong cc trng hp:- Khai bo cc method d kin sc thc thi.

- Khai bo mt interface cho mt object trong khi n i class ca n.- Kho st tng ng gia cc class m khng phi lin quan n cbc.

Protocols


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Cch khai bo mt protocol@protocol FooInterface

- (int) foo;

- (void) bar;

@end

Cch class chp nhn (adopt) protocol@interface MyClass: NSObject

Cc method khai bo trong protocol khng cn thit phi khai bo li tr@interface ca class.

Protocols


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ObjC c kh nng ng hn C v C++, mc d thc t rng n thngn ng bin dch trc tip m my mnh m. Di y l mt s vchc nng lin quan n reflection:

o isKindOfClass:[MyClass class] - cho bit rng object c class MyClass hay khng.

o isMemberOfClass:[MyClass class] - cho bt rng class ca objecMyClass hay khng.

o respondsToSelector:@selector(doIt) - cho bit rng object c methkhng.

o performSelector:@selector(doIt) - gi method c chnh doIt: c

Reflection


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Exceptions lm vic ging nh trong tt c cc ngn ng hin i kc i din bi cc class k tha (thng thng) tNSException, cc t kho @try, @catch v @finally chn cc exception ri nm mt block (khi) v x l chng. S dng @throw e nm ra exceptio

Hai method c th hu ch trong debug (g li):o NSAssert(x != 0, @"X must not be zero"); - a ra exception nu x o NSLog(@result: x = %@", x); - ghi ra mn hnh console chui, v

mt vi dng vo /var/log/system.log.

Exceptions & debugg


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Cc object trong ObjC l reference counted(tham chiu m).o

Cc object bt u vi reference l 1.o Tng reference vi method retain.o Gim reference vi method release, autorelease.o Khi s lng reference l 0, runtime (trnh bin dch) s gi method

Khi bn nm quyn s hu mt object, khi to object bng cc methtn bt u vi alloc, new hoc copy (v d, alloc, allocWithZone

hoc mutableCopy) hoc gi mt message retain, bn phi c trchphng quyn s hu object bng cch s dng release hoc autok khi no bn nhn c mt object (khng phi t mnh khi to)c release n.

T iOS 4.3 v sau h tr qun l b nh tng (ARC) vi garbagARC thc s gip developer d dng loi b memory leaks(tht thot

Memory manageme


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@implementationBankAccount

- (NSString *)accountNumber {

return [[accountNumberretain] autorelease];}

- (void)SetAccountNumber {

if(accountNumber != newNumber) {

[accountNumberrelease];

accountNumber = [newNumberretain];

}}

- (void)dealloc {

[selfsetAccountNumber:nil];

[superdealloc];

}

@end

retain/release/autorel

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