淺談iOS中幾個(gè)常用協(xié)議 NSCopying/NSMutableCopying

更新時(shí)間：2017年12月27日 09:28:38 作者：小洋子

下面小編就為大家分享一篇淺談iOS中幾個(gè)常用協(xié)議 NSCopying/NSMutableCopying，具有很好的參考價(jià)值，希望對(duì)大家有所幫助。一起跟隨小編過(guò)來(lái)看看吧

1、幾點(diǎn)說(shuō)明

說(shuō)到NSCopying和NSMutableCopying協(xié)議，不得不說(shuō)的就是copy和mutableCopy。

如果類想要支持copy操作，則必須實(shí)現(xiàn)NSCopying協(xié)議，也就是說(shuō)實(shí)現(xiàn)copyWithZone方法;

如果類想要支持mutableCopy操作，則必須實(shí)現(xiàn)NSMutableCopying協(xié)議，也就是說(shuō)實(shí)現(xiàn)mutableCopyWithZone方法;

iOS系統(tǒng)中的一些類已經(jīng)實(shí)現(xiàn)了NSCopying或者NSMutableCopying協(xié)議的方法，如果向未實(shí)現(xiàn)相應(yīng)方法的系統(tǒng)類或者自定義類發(fā)送copy或者mutableCopy消息，則會(huì)crash。

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Person copyWithZone:]: unrecognized selector sent to instance 0x6080000314c0'

發(fā)送copy和mutableCopy消息，均是進(jìn)行拷貝操作，但是對(duì)不可變對(duì)象的非容器類、可變對(duì)象的非容器類、可變對(duì)象的容器類、不可變對(duì)象的容器類中復(fù)制的方式略有不同；但如下兩點(diǎn)是相同的：

發(fā)送copy消息，拷貝出來(lái)的是不可變對(duì)象;

發(fā)送mutableCopy消息，拷貝出來(lái)的是可變對(duì)象;

故如下的操作會(huì)導(dǎo)致crash

NSMutableString *test1 = [[NSMutableString alloc]initWithString:@"11111"];
NSMutableString *test2 = [test1 copy];
[test2 appendString:@"22222"];

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSTaggedPointerString appendString:]: unrecognized selector sent to

2、系統(tǒng)非容器類

系統(tǒng)提供的非容器類中，如NSString,NSMutableString，有如下特性：

向不可變對(duì)象發(fā)送copy，進(jìn)行的是指針拷貝；向不可變對(duì)象發(fā)送mutalbeCopy消息，進(jìn)行的是內(nèi)容拷貝；

NSString *test3 = @"111111";
NSString *test4 = [test3 copy];
NSMutableString *test5 = [test3 mutableCopy];
NSLog(@"test3 is %p, test4 is %p, tast5 is %p",test3,test4,test5);
test3 is 0x10d6bb3a8, test4 is 0x10d6bb3a8, tast5 is 0x600000073e80

向可變對(duì)象發(fā)送copy和mutableCopy消息，均是深拷貝，也就是說(shuō)內(nèi)容拷貝；

NSMutableString *test11 = [[NSMutableString alloc]initWithString:@"444444"];
NSString *test12 = [test11 copy]; 
NSMutableString *test13 = [test11 mutableCopy]; 
NSLog(@"test11 is %p, test12 is %p, tast13 is %p",test11,test12,test13);
 
test11 is 0x600000073e00, test12 is 0xa003434343434346, tast13 is 0x600000073dc0

3、系統(tǒng)容器類

系統(tǒng)提供的容器類中，如NSArray,NSDictionary，有如下特性：

不可變對(duì)象copy，是淺拷貝，也就是說(shuō)指針復(fù)制；發(fā)送mutableCopy，是深復(fù)制，也就是說(shuō)內(nèi)容復(fù)制;

NSArray *array = [NSArray arrayWithObjects:@"1", nil];
NSArray *copyArray = [array copy];
NSMutableArray *mutableCopyArray = [array mutableCopy];
NSLog(@"array is %p, copyArray is %p, mutableCopyArray is %p", array, copyArray, mutableCopyArray);
array is 0x60800001e580, copyArray is 0x60800001e580, mutableCopyArray is 0x608000046ea0

可變對(duì)象copy和mutableCopy均是單層深拷貝，也就是說(shuō)單層的內(nèi)容拷貝；

NSMutableArray *element = [NSMutableArray arrayWithObject:@1];
NSMutableArray *array = [NSMutableArray arrayWithObject:element];
NSArray *copyArray = [array copy];
NSMutableArray *mutableCopyArray = [array mutableCopy];
NSLog(@"array is %p, copyArray is %p, mutableCopyArray is %p", array, copyArray, mutableCopyArray);
[mutableCopyArray[0] addObject:@2];
NSLog(@"element is %@, array is %@, copyArray is %@, mutableCopyArray is %@", element,array,copyArray, mutableCopyArray);
 
2017-02-22 11:53:25.286 test[91520:3915695] array is 0x600000057670, copyArray is 0x600000000bc0, mutableCopyArray is 0x6080000582a0
2017-02-22 11:53:25.287 test[91520:3915695] element is (
1,
2
), array is (
 (
 1,
 2
)
), copyArray is (
 (
 1,
 2
)
), mutableCopyArray is (
 (
 1,
 2
)
)

4、自定義的類

重要說(shuō)明：

1、所以的代碼設(shè)計(jì)均是針對(duì)業(yè)務(wù)需求。

2、對(duì)于自定義的類，決定能否向?qū)ο蟀l(fā)送copy和mutableCopy消息也是如此；

1、@property 聲明中用 copy 修飾

不得不說(shuō)下copy和strong在復(fù)制時(shí)候的區(qū)別，此處不講引用計(jì)數(shù)的問(wèn)題。

copy：拷貝一份不可變副本賦值給屬性；所以當(dāng)原對(duì)象值變化時(shí)，屬性值不會(huì)變化；

strong：有可能指向一個(gè)可變對(duì)象,如果這個(gè)可變對(duì)象在外部被修改了,那么會(huì)影響該屬性；

@interface Person : NSObject 
@property (nonatomic, copy) NSString *familyname;
@property (nonatomic, strong) NSString *nickname;
@end
Person *p1 = [[Person alloc]init];
 
NSMutableString *familyname = [[NSMutableString alloc]initWithString:@"張三"];
p1.familyname = familyname;
[familyname appendString:@"峰"];
 
NSLog(@"p1.familyname is %@",p1.familyname);
 
NSMutableString *nickname = [[NSMutableString alloc]initWithString:@"二狗"];
p1.nickname = nickname;
[nickname appendString:@"蛋兒"];
 
NSLog(@"p1.nickname is %@", p1.nickname);
2017-02-22 13:53:58.979 test[98299:3978965] p1.familyname is 張三
2017-02-22 13:53:58.979 test[98299:3978965] p1.nickname is 二狗蛋兒

2、類的對(duì)象的copy

此處唯一需要說(shuō)明的一點(diǎn)就是注意類的繼承。

這篇文章有非常清晰詳細(xì)的說(shuō)明，此處只照搬下結(jié)論：

1 類直接繼承自NSObject，無(wú)需調(diào)用[super copyWithZone:zone]

2 父類實(shí)現(xiàn)了copy協(xié)議，子類也實(shí)現(xiàn)了copy協(xié)議，子類需要調(diào)用[super copyWithZone:zone]

3 父類沒(méi)有實(shí)現(xiàn)copy協(xié)議，子類實(shí)現(xiàn)了copy協(xié)議，子類無(wú)需調(diào)用[super copyWithZone:zone]

4、copyWithZone方法中要調(diào)用[[[self class] alloc] init]來(lái)分配內(nèi)存

5、NSCopying

NSCopying是對(duì)象拷貝的協(xié)議。

類的對(duì)象如果支持拷貝，該類應(yīng)遵守并實(shí)現(xiàn)NSCopying協(xié)議。

NSCopying協(xié)議中的方法只有一個(gè)，如下：
- (id)copyWithZone:(NSZone *)zone { 
 Person *model = [[[self class] allocWithZone:zone] init];
 model.firstName = self.firstName;
 model.lastName = self.lastName;
 //未公開(kāi)的成員
 model->_nickName = _nickName;
 return model;
}

3、NSMutableCopying

當(dāng)自定義的類有一個(gè)屬性是可變對(duì)象時(shí)，對(duì)此屬性復(fù)制時(shí)要執(zhí)行mutableCopyWithZone操作。

- (id)copyWithZone:(NSZone *)zone {
 AFHTTPRequestSerializer *serializer = [[[self class] allocWithZone:zone] init];
 serializer.mutableHTTPRequestHeaders = [self.mutableHTTPRequestHeaders mutableCopyWithZone:zone];
 serializer.queryStringSerializationStyle = self.queryStringSerializationStyle;
 serializer.queryStringSerialization = self.queryStringSerialization;
 
 return serializer;
}

以上這篇淺談iOS中幾個(gè)常用協(xié)議 NSCopying/NSMutableCopying就是小編分享給大家的全部?jī)?nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。

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