1、几点说明
说到NSCopying和NSMutableCopying协议，不得不说的就是copy和mutableCopy。
- 如果类想要支持copy操作，则必须实现NSCopying协议，也就是说实现copyWithZone方法;
- 如果类想要支持mutableCopy操作，则必须实现NSMutableCopying协议，也就是说实现mutableCopyWithZone方法;
- iOS系统中的一些类已经实现了NSCopying或者NSMutableCopying协议的方法，如果向未实现相应方法的系统类或者自定义类发送copy或者mutableCopy消息，则会crash。
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Person copyWithZone:]: unrecognized selector sent to instance 0x6080000314c0'
发送copy和mutableCopy消息，均是进行拷贝操作，但是对不可变对象的非容器类、可变对象的非容器类、可变对象的容器类、不可变对象的容器类中复制的方式略有不同；但如下两点是相同的：
发送copy消息，拷贝出来的是不可变对象;
发送mutableCopy消息，拷贝出来的是可变对象;
故如下的操作会导致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、系统非容器类
系统提供的非容器类中，如NSString,NSMutableString，有如下特性：
- 向不可变对象发送copy，进行的是指针拷贝；向不可变对象发送mutalbeCopy消息，进行的是内容拷贝；
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
- 向可变对象发送copy和mutableCopy消息，均是深拷贝，也就是说内容拷贝；
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、系统容器类
系统提供的容器类中，如NSArray,NSDictionary，有如下特性：
- 不可变对象copy，是浅拷贝，也就是说指针复制；发送mutableCopy，是深复制，也就是说内容复制;
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
- 可变对象copy和mutableCopy均是单层深拷贝，也就是说单层的内容拷贝；
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、自定义的类
重要说明：
1、所以的代码设计均是针对业务需求。
2、对于自定义的类，决定能否向对象发送copy和mutableCopy消息也是如此；
1、@property 声明中用 copy 修饰
不得不说下copy和strong在复制时候的区别，此处不讲引用计数的问题。
copy：拷贝一份不可变副本赋值给属性；所以当原对象值变化时，属性值不会变化；
strong：有可能指向一个可变对象,如果这个可变对象在外部被修改了,那么会影响该属性；
@interface Person : NSObject
@property (nonatomic, copy) NSString *familyname;
@property (nonatomic, strong) NSString *nickname;
@end
Person *p1 = [[Person alloc]init];
NSMutableString *familyname = [[NSMutableString alloc]initWithString:@"张三"];
p1.familyname = familyname;
[familyname appendString:@"峰"];
NSLog(@"p1.familyname is %@",p1.familyname);
NSMutableString *nickname = [[NSMutableString alloc]initWithString:@"二狗"];
p1.nickname = nickname;
[nickname appendString:@"蛋儿"];
NSLog(@"p1.nickname is %@", p1.nickname);
2017-02-22 13:53:58.979 test[98299:3978965] p1.familyname is 张三
2017-02-22 13:53:58.979 test[98299:3978965] p1.nickname is 二狗蛋儿
2、类的对象的copy
此处唯一需要说明的一点就是注意类的继承。
这篇文章有非常清晰详细的说明，此处只照搬下结论：
- 1 类直接继承自NSObject，无需调用[super copyWithZone:zone]
- 2 父类实现了copy协议，子类也实现了copy协议，子类需要调用[super copyWithZone:zone]
- 3 父类没有实现copy协议，子类实现了copy协议，子类无需调用[super copyWithZone:zone]
- 4、copyWithZone方法中要调用[[[self class] alloc] init]来分配内存
5、NSCopying
- NSCopying是对象拷贝的协议。
- 类的对象如果支持拷贝，该类应遵守并实现NSCopying协议。
- NSCopying协议中的方法只有一个，如下：
- (id)copyWithZone:(NSZone *)zone {
Person *model = [[[self class] allocWithZone:zone] init];
model.firstName = self.firstName;
model.lastName = self.lastName;
//未公开的成员
model->_nickName = _nickName;
return model;
}
2、NSMutableCopying
当自定义的类有一个属性是可变对象时，对此属性复制时要执行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;
}
5、参考文章：
http://www.jianshu.com/p/cfdbd4d7f162
http://blog.csdn.net/qq_18425655/article/details/51325921
https://www.oschina.net/question/2330001_2181415
https://www.zybuluo.com/MicroCai/note/50592
