我正在学习ios开发，我对Objective-C中的深度复制感到困惑。例如，我下面有三节课。现在我想深入复制ClassA，任何人都可以教我完成复制方法吗？
A：
@interface ClassA : NSObject <NSCopying>
@property (nonatomic, assign) int aInt;
@property (nonatomic, retain) ClassB *bClass;
@end
B：
@interface ClassB : NSObject <NSCopying>
@property (nonatomic, assign) int bInt;
@property (nonatomic, retain) ClassC *cClass;
@end
C：
@interface ClassC : NSObject <NSCopying>
@property (nonatomic, assign) int cInt;
@property (nonatomic, copy) NSString *str;
@end
您应该在要复制的每个类中添加copyWithZone:方法。
NB：我手写这个，小心打字错误。
-(id) copyWithZone:(NSZone *) zone
{
ClassA *object = [super copyWithZone:zone];
object.aInt = self.aInt;
object.bClass = [self.bClass copyWithZone:zone];
return object;
}
-(id) copyWithZone:(NSZone *) zone
{
ClassB *object = [super copyWithZone:zone];
object.bInt = self.bInt;
object.cClass = [self.cClass copyWithZone:zone];
return object;
}
-(id) copyWithZone:(NSZone *) zone
{
ClassC *object = [super copyWithZone:zone];
object.cInt = self.cInt;
object.str = [self.str copy];
return object;
}
继http://www.techotopia.com/index.php/Copying_Objects_in_Objective-C解释之后
“这可以通过将对象及其组成元素写入存档然后读回新对象来实现。”
@implementation ClassA
- (id)copyWithZone:(NSZone*)zone{
NSData *buffer;
buffer = [NSKeyedArchiver archivedDataWithRootObject:self];
ClassA *copy = [NSKeyedUnarchiver unarchiveObjectWithData: buffer];
return copy;
}
@end
iOS上的Objective-C不提供任何直接语言或库构造来在浅拷贝和深拷贝之间切换。每个类定义“获取其副本”的含义：
@implementation ClassA
- (id) copyWithZone: (NSZone*) zone
{
ClassA *copy = [super copyWithZone:zone];
[copy setBClass:bClass]; // this would be a shallow copy
[copy setBClass:[bClass copy]]; // this would be a deep copy
return copy;
}
@end
当然，你必须在ClassB和ClassC中做同样的决定。如果我没有弄错，Objective-C中副本的通常语义是返回浅表副本。有关该主题的更多讨论，另请参阅this question about copying arrays。
我有自定义类的长属性列表，所以我迭代它们：
@interface MyClass : NSObject <NSCopying>
#import <objc/runtime.h>
-(id) copyWithZone: (NSZone *) zone {
MyClass *myCopy = [[MyClass alloc] init];
//deepCopy
unsigned int numOfProperties;
objc_property_t *properties = class_copyPropertyList([self class], &numOfProperties);
for (int i = 0; i < numOfProperties; i++) {
objc_property_t property = properties[i];
NSString *propertyName = [[NSString alloc]initWithCString:property_getName(property) encoding:NSUTF8StringEncoding];
[adressCopy setValue:[[self valueForKey:propertyName] copy] forKey:propertyName];
}
return myCopy;
}
所有customClassProperties也需要实现它。
这可能会有所帮助。该链接显示了如何使用NSKeyedArchiver进行深层复制
http://iphonecodecenter.wordpress.com/2013/08/26/difference-between-shallow-copy-and-deep-copy/
Objective-C的copy和copyWithZone规范是伪造和危险的，不应该使用。 - ！ - 至少在与ARC（自动参考计数）一起使用时（2016-08-23） - ！ - 代码将导致写出内存/缓冲区溢出的范围。相反，我提出了一种方法来安全地复制对象initAsShallowCopy和deepCopy。
在下面的代码中查看我的测试结果：
#import <Foundation/Foundation.h>
@interface ClassA : NSObject
{
@public
NSMutableString* A_Name;
NSInteger A_NSInteger;
long int A_int;
float A_float;
}
-(id)init;
-(id)copyWithZone:(NSZone *) zone; // DON'T USE copy OR copyWithZone, unless you ignore Apple's guidelines and always make shallow copies in line with the correct example code here for initAsShallowCopy (but you return a copy instead of being a copy)
-(id)initAsShallowCopy:(ClassA *)original; // Correct way to make a shallow copy
-(void)deepCopy; // Correct way to make a deep copy (Call initAsShallowCopy first)
@end
@interface ClassB : ClassA
{
@public
NSMutableString* B_Name;
NSInteger B_NSInteger;
long int B_int;
float B_float;
}
-(id)init;
-(id)copyWithZone:(NSZone *) zone; // DON'T USE copy OR copyWithZone, unless you ignore Apple's guidelines and always make shallow copies in line with the correct example code here for initAsShallowCopy (but you return a copy instead of being a copy)
-(id)initAsShallowCopy:(ClassB *)original; // Correct way to make a shallow copy
-(void)deepCopy; // Correct way to make a deep copy (Call initAsShallowCopy first)
-(void)print;
@end
@interface ClassCWithoutCopy : NSObject
{
@public
NSMutableString* C_Name;
NSInteger C_NSInteger;
long int C_int;
float C_float;
}
-(id)init;
-(void)print;
@end
@implementation ClassA
-(id)init
{
if ( self = [super init] ) { // initialize NSObject
//A_Name = [[NSMutableString alloc] init];
//[A_Name setString:@"I am inited to A"];
A_Name = [NSMutableString stringWithString:@"I am inited to A"];
A_NSInteger = 1;
A_int = 1;
A_float = 1.0;
return self;
}
return nil;
}
/*
FROM https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/#//apple_ref/occ/instm/NSObject/copy
-- NSObject Class Reference --
- (id)copy
Discussion
This is a convenience method for classes that adopt the NSCopying protocol. An exception is raised if there is
no implementation for copyWithZone:.
NSObject does not itself support the NSCopying protocol. Subclasses must support the protocol and
implement the copyWithZone: method. A subclass version of the copyWithZone: method should send the message to super first,
to incorporate its implementation, unless the subclass descends directly from NSObject.
+ copyWithZone:
Discussion
This method exists so class objects can be used in situations where you need an object that conforms to the NSCopying protocol.
For example, this method lets you use a class object as a key to an NSDictionary object.
You should not override this method.
CONCLUSION
copy says we should incorporate the implementation of copyWithZone, while copyWithZone says we should not override it.. So what is it?
Looking at copyWithZone, we see that it is a class method (+), meaning it has not access to its instantiated members.
So maybe they mean, we should not override the class method (+), but we should implement its instance method -copyWithZone:
!!In any case we should not implement copy, because it is just made for convenience by Apple!!
FROM: https://developer.apple.com/library/tvos/documentation/Cocoa/Reference/Foundation/Protocols/NSCopying_Protocol/index.html
-- NSCopying --
Your options for implementing this protocol are as follows:
1) Implement NSCopying using alloc and init... in classes that don’t inherit copyWithZone:.
2) Implement NSCopying by invoking the superclass’s copyWithZone: when NSCopying behavior is inherited.
If the superclass implementation might use the NSCopyObject function, make explicit assignments to
pointer instance variables for retained objects.
3) Implement NSCopying by retaining the original instead of creating a new copy when the class and its contents are immutable.
CONCLUSION:
From 1) NSObject does not implement copyWithZone so any class that you make that should support copying should call [[Class alloc] init].
From 2) Any subclass of a copyable object should call [super copyWithZone:zone], but NOT [[Class alloc] init] !!!!!!
*/
-(id) copyWithZone:(NSZone *) zone
{
ClassA *CopiedObject = [[ClassA alloc] init];
if(CopiedObject){
CopiedObject->A_Name = [A_Name copy];
CopiedObject->A_NSInteger = A_NSInteger;
CopiedObject->A_int = A_int;
CopiedObject->A_float = A_float;
return CopiedObject;
}
return nil;
}
-(id)initAsShallowCopy:(ClassA *)original // Correct way to make a shallow copy
{
/* Why this has to be done like this:
It is very annoying to assign every variable explicitely.
However this has to be done, in order for ARC (Automatic Reference Counting) (2016-08-23) to work.
The compiler needs to be aware of any reference made to an object or reference cleared to an object in order to keep track of the
reference counts.
The danger is that when you add a variable to you class later on, you must not forget to update your initAsShallowCopy function and
possibly your DeepCopy function.
It would be much nicer if you could just do:
*self = *original;
But that gives compiler error:
/DeepCopyTest/main.m:135:9: Cannot assign to class object ('ClassA' invalid)
So therefore there is also no raw memory copy between objects,
so we are stuck with writing out each member variable explicitely.
*/
if ( self = [super init] ) { // initialize NSObject
A_Name = original->A_Name;
A_NSInteger = original->A_NSInteger;
A_int = original->A_int;
A_float = original->A_float;
return self;
}
return nil;
}
-(void)deepCopy; // Correct way to make a deep copy (Call initAsShallowCopy first)
{
/* Luckily now, we only have to duplicate the objects that require a deep copy.
So we don't have to write out all the floats, ints and NSIntegers, etcetera. Thus only the pointers (*) to objects.
*/
A_Name = [A_Name copy];
}
@end
@implementation ClassB
-(id)init
{
if ( self = [super init] ) { // initialize ClassA
B_Name = [NSMutableString stringWithString:@"I am inited to B"];
B_NSInteger = 2;
B_int = 2;
B_float = 2.0;
return self;
}
return nil;
}
-(id) copyWithZone:(NSZone *) zone
{
//ClassA *CopiedObject = [[ClassA alloc] init]; We are not a direct descendant from NSObject, so don't call alloc-init
// instead call the super copyWithZone
ClassB *CopiedObject = [super copyWithZone:zone]; /* Using ARC (Automatic Reference Counting) 2016-08-23:
THIS IS A MASSIVE BUFFER OVERFLOW/WRITING OUT OF BOUNDS RISK:
Since super now allocates the object, it will now only allocate an object of size ClassA
and effectively allocate too little memory for the ClassB. Unless memory allocation is upgraded to work with magic for
Objective-C, DON'T USE copy or copyWithZone!!!!
*/
if(CopiedObject){
CopiedObject->B_Name = [B_Name copy];
CopiedObject->B_NSInteger = B_NSInteger;
CopiedObject->B_int = B_int;
CopiedObject->B_float = B_float;
return CopiedObject;
}
return nil;
}
-(id)initAsShallowCopy:(ClassB *)original // Correct way to make a shallow copy
{
if ( self = [super initAsShallowCopy:original] ) { // initialize ClassA
B_Name = original->B_Name;
B_NSInteger = original->B_NSInteger;
B_int = original->B_int;
B_float = original->B_float;
return self;
}
return nil;
}
-(void)deepCopy; // Correct way to make a deep copy (Call initAsShallowCopy first)
{
/* Luckily now, we only have to duplicate the objects that require a deep copy.
So we don't have to write out all the floats, ints and NSIntegers, etcetera. Thus only the pointers (*) to objects.
*/
[super deepCopy];
B_Name = [B_Name copy];
}
-(void)print
{
NSLog(@"A_Name=\"%@\", A_NSInteger=%ld,A_int=%ld,A_float=%f",A_Name,A_NSInteger,A_int,A_float);
NSLog(@"B_Name=\"%@\", B_NSInteger=%ld,B_int=%ld,B_float=%f",B_Name,B_NSInteger,B_int,B_float);
}
@end
@implementation ClassCWithoutCopy
-(id)init
{
if ( self = [super init] ) { // initialize NSObject
C_Name = [NSMutableString stringWithString:@"I am inited to C"];
C_NSInteger = 3;
C_int = 3;
C_float = 3.0;
return self;
}
return nil;
}
-(void)print
{
NSLog(@"C_Name=\"%@\", C_NSInteger=%ld,C_int=%ld,C_float=%f",C_Name,C_NSInteger,C_int,C_float);
}
@end
int main(int argc, const char * argv[]) {
@autoreleasepool {
ClassB *OriginalB;
ClassB *CopiedB;
#define USE_CORRECT_DEEP_COPY_AND_SHALLOW_COPY 1
#define USE_CLASSC_WITHOUT_COPY_TEST 0
#if(USE_CLASSC_WITHOUT_COPY_TEST)
ClassCWithoutCopy *OriginalC;
ClassCWithoutCopy *CopiedC;
OriginalC = [[ClassCWithoutCopy alloc] init];
CopiedC = [OriginalC copy]; /* Thread 1: signal SIGABRT: libc++abi.dylib: terminating with uncaught exception of type NSException
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ClassCWithoutCopy copyWithZone:]: unrecognized selector sent to instance 0x100100450' */
//CopiedC = [ClassCWithoutCopy copyWithZone:nil]; /* DeepCopyTest/main.m:283:33: 'copyWithZone:' is unavailable: not available in automatic reference counting mode
*/
NSLog(@"OriginalC print:1");
[OriginalC print];
NSLog(@"CopiedC print:1");
[CopiedC print];
[OriginalC->C_Name appendString:@" and Appended as the original"];
OriginalC->C_NSInteger = 30;
OriginalC->C_int = 30;
OriginalC->C_float = 30.0;
NSLog(@"OriginalC print:2");
[OriginalC print];
NSLog(@"CopiedC print:2");
[CopiedC print];
#endif
#if(USE_CORRECT_DEEP_COPY_AND_SHALLOW_COPY)
OriginalB = [[ClassB alloc] init];
CopiedB = [[ClassB alloc] initAsShallowCopy:OriginalB];
NSLog(@"OriginalB print:1");
[OriginalB print];
NSLog(@"CopiedB print:1");
[CopiedB print];
[OriginalB->A_Name appendString:@" and Appended as the original"];
OriginalB->A_NSInteger = 10;
OriginalB->A_int = 10;
OriginalB->A_float = 10.0;
[OriginalB->B_Name appendString:@" and Appended as the original"];
OriginalB->B_NSInteger = 20;
OriginalB->B_int = 20;
OriginalB->B_float = 20.0;
NSLog(@"OriginalB print:2");
[OriginalB print];
NSLog(@"CopiedB print:2");
[CopiedB print];
// This works as expected: The values of OriginalB and CopiedB differ, but the shallow copied strings are the same.
// Now make a deep copy of CopiedB
[CopiedB deepCopy];
[OriginalB->A_Name appendString:@" and Appended twice as the original"];
OriginalB->A_NSInteger = 100;
OriginalB->A_int = 100;
OriginalB->A_float = 100.0;
[OriginalB->B_Name appendString:@" and Appended twice as the original"];
OriginalB->B_NSInteger = 200;
OriginalB->B_int = 200;
OriginalB->B_float = 200.0;
NSLog(@"OriginalB print:3");
[OriginalB print];
NSLog(@"CopiedB print:3");
[CopiedB print];
// This works as expected: The values of OriginalB and CopiedB differ and als the deep copied strings are different.
#else
OriginalB = [[ClassB alloc] init];
CopiedB = [OriginalB copy]; // Undefined behaviour. You will write unallocated memory
NSLog(@"OriginalB print:1");
[OriginalB print];
NSLog(@"CopiedB print:1");
/*[CopiedB print]; / * Thread 1: signal SIGABRT: libc++abi.dylib: terminating with uncaught exception of type NSException
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ClassA print]: unrecognized selector sent to instance 0x10010ad60' */
NSLog(@"A_Name=\"%@\", A_NSInteger=%ld,A_int=%ld,A_float=%f",CopiedB->A_Name,CopiedB->A_NSInteger,CopiedB->A_int,CopiedB->A_float);
NSLog(@"B_Name=\"%@\", B_NSInteger=%ld,B_int=%ld,B_float=%f",CopiedB->B_Name,CopiedB->B_NSInteger,CopiedB->B_int,CopiedB->B_float); // Undefined behaviour. You will read unallocated memory
[OriginalB->A_Name appendString:@" and Appended as the original"];
OriginalB->A_NSInteger = 10;
OriginalB->A_int = 10;
OriginalB->A_float = 10.0;
[OriginalB->B_Name appendString:@" and Appended as the original"];
OriginalB->B_NSInteger = 20;
OriginalB->B_int = 20;
OriginalB->B_float = 20.0;
// This at least works: Changing Original, does not alter the values of Copy.
NSLog(@"OriginalB print:2");
[OriginalB print];
NSLog(@"CopiedB print:2");
NSLog(@"A_Name=\"%@\", A_NSInteger=%ld,A_int=%ld,A_float=%f",CopiedB->A_Name,CopiedB->A_NSInteger,CopiedB->A_int,CopiedB->A_float);
//NSLog(@"B_Name=\"%@\", B_NSInteger=%ld,B_int=%ld,B_float=%f",CopiedB->B_Name,CopiedB->B_NSInteger,CopiedB->B_int,CopiedB->B_float); // Undefined behaviour. You will read unallocated memory
/*[CopiedB->A_Name appendString:@" and Appended as the copy"]; / * Thread 1: signal SIGABRT: libc++abi.dylib: terminating with uncaught exception of type NSException
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Attempt to mutate immutable object with appendString:' */
CopiedB->A_NSInteger = 100;
CopiedB->A_int = 100;
CopiedB->A_float = 100.0;
/*[CopiedB->B_Name appendString:@" and Appended as the copy"]; / * Thread 1: signal SIGABRT: libc++abi.dylib: terminating with uncaught exception of type NSException
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Attempt to mutate immutable object with appendString:'*/
CopiedB->B_NSInteger = 200; // Undefined behaviour. You will write unallocated memory
CopiedB->B_int = 200; // Undefined behaviour. You will write unallocated memory
CopiedB->B_float = 200.0; // Undefined behaviour. You will write unallocated memory
/* Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
DeepCopyTest(2376,0x7fff7edda310) malloc: *** error for object 0x10010ad98: incorrect checksum for freed object - object was probably modified after being freed.
*** set a breakpoint in malloc_error_break to debug */
NSLog(@"OriginalB print after modification of CopiedB:");
[OriginalB print];
NSLog(@"CopiedB print after modification of CopiedB:");
/*[CopiedB print];; / * Thread 1: signal SIGABRT: libc++abi.dylib: terminating with uncaught exception of type NSException
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ClassA print]: unrecognized selector sent to instance 0x10010ad60' */
#endif
}
return 0;
}
PS-1：来自：
- 对象复制 -
深拷贝复制引用的对象，而浅拷贝仅复制对这些对象的引用。因此，如果对象A被浅层复制到对象B，则对象B引用对象A引用的相同实例变量（或属性）。深度复制对象比浅层复制更受欢迎，尤其是对于值对象。
注意：
这是不明确的表述，特别是附带的插图，这表明错误的解释。
这个公式使得对同一对象的两个引用看起来像一个浅拷贝。这不是真的。它根本不是副本。
明确的表述是： - 对象的浅表副本具有从其父对象复制的所有值和引用，但它本身是内存中的唯一对象。 - 对象的深层副本具有从其父对象复制的所有值，并且本身是内存中的唯一对象，但现在所有引用都引用-deep本身 - 原始引用对象的副本。
虽然深度复制的确切实现可能不会100％给出深层复制。指向外部引用的对象（例如硬件项或图形驱动程序不能复制，但只增加引用计数）某些深度复制没有功能意义。对象可能引用它所在的窗口，但复制窗口没有意义。对象也可能引用被认为是不可变的数据，因此复制该数据效率不高。
PS-2：在我尝试手动格式化所有代码之前，你可以给我一些ctrl-K的提示。
PS-3：Apple-Z（撤消）撤消我的所有格式而不是最后一个，我无法重做它。