浅copy ：拷贝的是对象本身，两个对象指向同一块内存空间。
深copy ：重新开辟内存空间，两个对象指向不同的内存空间。
浅copy图示
image
深copy图示
image
从上图可以看出，浅拷贝A指针改变了所指向的内容，B指针也指向被修改后的内容。如果有些地方用到B指针，不希望在A指向的内容发生变化时也跟着变化，则需要用到深拷贝。
通俗理解为:浅拷贝好比你的影子，你死了，影子也没了；深拷贝好比克隆人，你死了，它还在。
本质区别
深拷贝和浅拷贝的本质是地址是否相同
在开发过程中，大体上会区分为对象和容器两个概念，对象的copy是浅拷贝，mutablecopy是深拷贝。
容器包含对象的拷贝，无论是copy，还是mutablecopy都是浅拷贝，要想实现对象的深拷贝，必须自己提供拷贝方法。
- 非容器不可变对象：NSString
- 非容器可变对象： NSMutableString
- 容器类不可变对象： NSArray
- 容器类可变对象： NSMutableArray
对四种类型对象分别举例
非容器不可变对象
NSString *str1 = @"非容器不可变对象";
NSString *str2 = [str1 copy];
NSString *str3 = [str1 mutableCopy];
NSLog(@"str1_p : %p, class: %@", str1, [str1 class]);
NSLog(@"str2_p : %p, class: %@", str2, [str2 class]);
NSLog(@"str3_p : %p, class: %@", str3, [str3 class]);
输出
str1_p : 0x104c4a068, class: __NSCFConstantString
str2_p : 0x104c4a068, class: __NSCFConstantString
str3_p : 0x61000006db00, class: __NSCFString
结论：
对于非容器不可变对象的copy为浅拷贝，mutableCopy为深拷贝
浅拷贝获得的对象地址和原对象地址一致， 返回的对象为不可变对象
深拷贝返回新的内存地址，返回对象为可变对象
非容器可变对象
NSMutableString *str1 = [NSMutableString stringWithFormat:@"非容器可变对象"];
NSMutableString *str2 = [str1 copy];
NSMutableString *str3 = [str1 mutableCopy];
NSLog(@"str1_p : %p, class: %@", str1, [str1 class]);
NSLog(@"str2_p : %p, class: %@", str2, [str2 class]);
NSLog(@"str3_p : %p, class: %@", str3, [str3 class]);
输出
str1_p : 0x618000260140, class: __NSCFString
str2_p : 0x61800004efd0, class: __NSCFString
str3_p : 0x6180002602c0, class: __NSCFString
结论：
对于非容器可变对象的copy为深拷贝
mutableCopy为深拷贝
并且copy和mutableCopy返回对象都为可变对象
容器不可变对象
NSMutableString *str1 = [NSMutableString stringWithFormat:@"非容器可变对象"];
NSArray *array = [NSArray arrayWithObjects:str1, @"非容器不可变对象", nil];
NSArray *copyArray = [array copy];
NSArray *mutableCopyArray = [array mutableCopy];
NSLog(@"array_p: %p, class: %@", array, [array class]);
NSLog(@"copyArray_p: %p, class: %@", copyArray, [copyArray class]);
NSLog(@"mutableCopyArray_p: %p, class: %@", mutableCopyArray, [mutableCopyArray class]);
NSLog(@"======原对象=====");
NSLog(@"object_p: %p, class: %@", array[0], [array[0] class]);
NSLog(@"object_p: %p, class: %@", array[1], [array[1] class]);
NSLog(@"======copy对象=====");
NSLog(@"object_p: %p, class: %@", copyArray[0], [copyArray[0] class]);
NSLog(@"object_p: %p, class: %@", copyArray[1], [copyArray[1] class]);
NSLog(@"======mutableCopy对象=====");
NSLog(@"object_p: %p, class: %@", mutableCopyArray[0], [mutableCopyArray[0] class]);
NSLog(@"object_p: %p, class: %@", mutableCopyArray[1], [mutableCopyArray[1] class]);
输出：
array_p: 0x610000024ac0, class: __NSArrayI
copyArray_p: 0x610000024ac0, class: __NSArrayI
mutableCopyArray_p: 0x610000242610, class: __NSArrayM
======原对象=====
object_p: 0x61000006f540, class: __NSCFString
object_p: 0x10c386080, class: __NSCFConstantString
======copy对象=====
object_p: 0x61000006f540, class: __NSCFString
object_p: 0x10c386080, class: __NSCFConstantString
======mutableCopy对象=====
object_p: 0x61000006f540, class: __NSCFString
object_p: 0x10c386080, class: __NSCFConstantString
结论：
从上述输出中可以看出容器类不可变对象mutableCopy确实返回一个新的容器，但容器内的元素仍然是浅拷贝
容器可变对象
NSMutableString *str1 = [NSMutableString stringWithFormat:@"非容器可变对象"];
NSMutableArray *array = [NSMutableArray arrayWithObjects:str1, @"非容器不可变对象", nil];
NSMutableArray *copyArray = [array copy];
NSMutableArray *mutableCopyArray = [array mutableCopy];
NSLog(@"array_p: %p, class: %@", array, [array class]);
NSLog(@"copyArray_p: %p, class: %@", copyArray, [copyArray class]);
NSLog(@"mutableCopyArray_p: %p, class: %@", mutableCopyArray, [mutableCopyArray class]);
NSLog(@"======原对象=====");
NSLog(@"object_p: %p, class: %@", array[0], [array[0] class]);
NSLog(@"object_p: %p, class: %@", array[1], [array[1] class]);
NSLog(@"======copy对象=====");
NSLog(@"object_p: %p, class: %@", copyArray[0], [copyArray[0] class]);
NSLog(@"object_p: %p, class: %@", copyArray[1], [copyArray[1] class]);
NSLog(@"======mutableCopy对象=====");
NSLog(@"object_p: %p, class: %@", mutableCopyArray[0], [mutableCopyArray[0] class]);
NSLog(@"object_p: %p, class: %@", mutableCopyArray[1], [mutableCopyArray[1] class]);
输出：
array_p: 0x6100000552d0, class: __NSArrayM
copyArray_p: 0x610000031340, class: __NSArrayI
mutableCopyArray_p: 0x610000055000, class: __NSArrayM
======原对象=====
object_p: 0x610000267300, class: __NSCFString
object_p: 0x107070080, class: __NSCFConstantString
======copy对象=====
object_p: 0x610000267300, class: __NSCFString
object_p: 0x107070080, class: __NSCFConstantString
======mutableCopy对象=====
object_p: 0x610000267300, class: __NSCFString
object_p: 0x107070080, class: __NSCFConstantString
结论：
从上述输出中可以看出容器类可变对象mutableCopy和copy都返回一个新的容器，但容器内的元素仍然是浅拷贝
总结：
通过上述代码分析：
copy： 对于可变对象为深拷贝，对于不可变对象为浅拷贝
mutableCopy：始终是深拷贝
自定义类对象的深浅拷贝
在OC中不是所有的类都支持拷贝，只有遵循<NSCopying>才支持copy，只有遵循<NSMutableCopying>才支持mutableCopy。如果没有遵循，拷贝时会直接Crash。
代码：
#import <Foundation/Foundation.h>
@interface Person : NSObject <NSCopying, NSMutableCopying>
@property (nonatomic, copy) NSString *name;
@end
#import "Person.h"
@implementation Person
- (id)copyWithZone:(NSZone *)zone {
Person *person = [Person allocWithZone:zone];
person.name = self.name;
return person;
}
- (id)mutableCopyWithZone:(NSZone *)zone {
Person *person = [Person allocWithZone:zone];
person.name = self.name;
return person;
}
@end
实现容器对象的完全拷贝
NSMutableString *str1 = [NSMutableString stringWithFormat:@"非容器可变对象"];
NSArray *array = [NSArray arrayWithObjects:str1, @"非容器不可变对象", nil];
NSMutableArray *mutableArray = [[NSMutableArray alloc] initWithArray:array copyItems:YES];
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:mutableArray];
NSMutableArray *newMutableArray = [NSKeyedUnarchiver unarchiveObjectWithData:data];
NSLog(@"===原对象===");
NSLog(@"array[0] : %p, array[1] : %p", array[0], array[1]);
NSLog(@"===新对象===");
NSLog(@"mutableArray[0] : %p, mutableArray[1] : %p", mutableArray[0], mutableArray[1]);
NSLog(@"===完全拷贝对象===");
NSLog(@"newMutableArray[0] : %p, newMutableArray[1] : %p", newMutableArray[0], newMutableArray[1]);
输出：
===原对象===
array[0] : 0x6180000697c0, array[1] : 0x10f40f098
===新对象===
mutableArray[0] : 0x618000055060, mutableArray[1] : 0x10f40f098
===完全拷贝对象===
newMutableArray[0] : 0x618000055600, newMutableArray[1] : 0x6180000556f0
如果是自定义类对象 需要遵循<NSCoding>否则在使用NSKeyedArchiver的时候会Crash
自定义对象代码如下
#import <Foundation/Foundation.h>
@interface Person : NSObject <NSCoding>
@property (nonatomic, copy) NSString *name;
@end
#import "Person.h"
@implementation Person
- (instancetype)initWithCoder:(NSCoder *)aDecoder {
self.name = [aDecoder decodeObjectForKey:@"name"];
return self;
}
- (void)encodeWithCoder:(NSCoder *)aCoder {
[aCoder encodeObject:self.name forKey:@"name"];
}
@end
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