iOS中几个常用协议(一)NSCopying/NSMutableCopying)

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

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