iOS开发那些事儿（五）Objective-C浅拷贝与深拷贝

2022-10-20 19:49:03

浅拷贝：copy操作出来的对象指针直接指向模板的地址。即两个对象公用一块内存地址

 #import <Foundation/Foundation.h>

 int main(int argc, const char * argv[]) {

     @autoreleasepool {

         NSString * testStr          = @"connor";

         NSLog(@"testStr's Address   = %p",testStr);

         NSString * testStrCopy      = [testStr copy];

         NSLog(@"testStrCopy Address = %p",testStrCopy);

         NSArray * array             = @[@,@,@];

         NSLog(@"array Address       = %p",array);

         NSArray * copyArray         = [array copy];

         NSLog(@"copyArray Address   = %p",copyArray);

     }

     return ;

 }

输出结果如下：

DataStruct[11210:2189074] testStr's Address 　 = 0x100004280

DataStruct[11210:2189074] testStrCopy Address　= 0x100004280

DataStruct[11210:2189074] array Address = 0x100300650

DataStruct[11210:2189074] copyArray Address = 0x100300650

深拷贝：copy操作出来的对象指针直接指向新开辟的内存。即持有原对象的拷贝副本

 #import <Foundation/Foundation.h>

 #import "Father.h"

 int main(int argc, const char * argv[]) {

     @autoreleasepool {

         NSString * test     = @"a";

         NSLog(@"%p",test);

         NSString * testCopy = [test mutableCopy];

         NSLog(@"%p",testCopy);

     }

     return ;

 }

输出结果如下：

DataStruct[11355:2249168] 0x100004280

DataStruct[11355:2249168] 0x100203cf0

Foundation总结大致如下：
- 　　NS*类型的类调用Copy属于浅拷贝（例如NSString、NSArray等等）
- 　　NS*类型的类调用MutableCopy属于深拷贝（例如NSString、NSArray等等）
- 　　NSMutable*类型无论调用Copy或者MutableCopy都属于深拷贝
拷贝构造：以上我们谈的都是Foundation中用到的深浅拷贝，如果我们自己定义了一个类。怎么去实现它的深浅拷贝呢？这里就要用到拷贝构造方法。iOS中默认NSObject是不遵循NSCopying（不变副本）、NSMutableCopying（可变副本）的，所以如果想一个对象可Copy，就必须实现其中两个协议并且重写copyWithZone、mutableCopyWithZone方法。
- 　　下面我们定义一个Father类，来实现深拷贝：
```
 /** .h  */

 #import <Foundation/Foundation.h>

 @interface Father : NSObject<NSCopying>

 @property(nonatomic,copy)NSString * name;

 @end

 /** .m  */

 #import "Father.h"

 @implementation Father

 -(id)copyWithZone:(NSZone *)zone{

     Father * copyFather = [[self class]allocWithZone:zone];

     return copyFather;

 }

 @end
```
  写好了Father类我们在外界就可以利用copy的方法去copy出一个Father对象
```
 #import <Foundation/Foundation.h>

 #import "Father.h"

 int main(int argc, const char * argv[]) {

     @autoreleasepool {

         Father * fatherA = [[Father alloc]init];

         fatherA.name     = @"connor";

         NSLog(@"%p",fatherA);

         Father * fatherB = [fatherA copy];

         NSLog(@"%@",fatherB.name);

         NSLog(@"%p",fatherB);

     }

     return ;

 }
```
  输出结果：
  
  DataStruct[11383:2256524] 0x100206c80
  
  DataStruct[11383:2256524] (null)
  
  DataStruct[11383:2256524] 0x100300600
  
  从输出结果来看，两个Father实例的内存地址是不一样的我们实现了深拷贝。但是为什么第二个Father没有名字？在拷贝过程过虽然我是从你FatherA拷贝过来的，但是你并没有指定FatherA中的属性到底是什么方式拷贝过来。所以这里面如果想要实现名字也拷贝过来，需要我们自己去定义到底是深拷贝过来还是浅拷贝过来。这也符合苹果做事的风格嘛。
```
 #import "Father.h"

 //添加name的浅拷贝

 @implementation Father

 -(id)copyWithZone:(NSZone *)zone{

     Father * copyFather = [[self class]allocWithZone:zone];

     copyFather.name     = [self.name copy]; //如果想要深拷贝过来直接mutableCopy即可

     return copyFather;

 }

 @end
```
  结果输出两个name的内存地址：
  
  DataStruct[11409:2261412] 0x100004290
  
  DataStruct[11409:2261412] 0x100004290
- 现在情况改变了，Father平时出门需要开车。Father需要持有Car类。那这个时候我们要如果复制这个爸爸！（因为复制出来的Father不能和之前那个Father开一辆车，所以我们应该用深拷贝。过程很简单直接贴代码了！）
```
 /** .h */

 #import <Foundation/Foundation.h>

 @interface Car : NSObject<NSCopying>

 @property(nonatomic,copy)NSString * brand;

 @end

 /** .m */

 @implementation Car

 -(id)copyWithZone:(NSZone *)zone{

     Car * copyCar = [[self class]allocWithZone:zone];

     copyCar.brand = [self.brand mutableCopy];

     return copyCar;

 }

 @end
```
  Car
```
/** .h */

#import <Foundation/Foundation.h>

#import "Car.h"

@interface Father : NSObject<NSCopying>

@property(nonatomic,copy)NSString * name;

@property(nonatomic,strong)Car    * car;

@end

/** .m */

#import "Father.h"

@implementation Father

-(id)copyWithZone:(NSZone *)zone{

    Father * copyFather = [[self class]allocWithZone:zone];

    copyFather.name     = [self.name copy];

    copyFather.car      = [self.car copy];

    return copyFather;

}

@end
```
  Father
```
#import <Foundation/Foundation.h>

#import "Father.h"

#import "Car.h"

int main(int argc, const char * argv[]) {

    @autoreleasepool {

        Father * fatherA = [[Father alloc]init];

        fatherA.car      = [[Car alloc]init];

        NSLog(@"%p",fatherA.car);

        Father * fatherB = [fatherA copy];

        NSLog(@"%p",fatherB.car);

    }

    return ;

}
```
  main
  输出结果：
  
  DataStruct[11441:2268004] 0x100111f60
  
  DataStruct[11441:2268004] 0x1001154a0
- copy这种操作如果发生在继承关系之后就有什么样的效果？或者说1.父类实现了NSCopying，子类该如果实现NSCopying。2.父类没有实现NSCopying，子类如何实现NSCopying？要接一个问题我们先看下表象是什么，然后通过表象来分析问题并解决问题。接下来我们先试着用第一种情况来看看表象：Son继承于Father
```
 /** .h */

 #import "Father.h"

 @interface Son : Father

 @property(nonatomic,copy)NSString * toy;

 @end

 /** .m */

 #import "Son.h"

 @implementation Son

 @end
```
  Son
```
 #import <Foundation/Foundation.h>

 #import "Son.h"

 int main(int argc, const char * argv[]) {

     @autoreleasepool {

         Son * sonA = [[Son alloc]init];

         sonA.name  = @"connor";

         sonA.toy   = @"iPhone";

         Son * sonB = [sonA copy];

         NSLog(@"sonA's Address = %p",sonA);

         NSLog(@"sonB's Address = %p",sonB);

         NSLog(@"sonA's name Address = %p",sonA.name);

         NSLog(@"sonB's name Address = %p",sonB.name);

         NSLog(@"sonA's toy Address = %p",sonA.toy);

         NSLog(@"sonB's toy Address = %p",sonB.toy);

     }

     return ;

 }
```
  main
  输出结果：
  
  DataStruct[11563:2279201] sonA's Address 　　 = 0x100114bc0
  
  DataStruct[11563:2279201] sonB's Address = 0x100111f70
  
  DataStruct[11563:2279201] sonA's name Address = 0x100004260
  
  DataStruct[11563:2279201] sonB's name Address = 0x726f6e6e6f6365
  
  DataStruct[11563:2279201] sonA's toy Address = 0x100004280
  
  DataStruct[11563:2279201] sonB's toy Address = 0x0　　这个结果也在我们意料之内的嘛，Son是继承与Father类的，Father实现了Copy协议，所以这个copy协议实现会继承到子类。我的理解其实：当Son调用Copy方法的时候就将消息转发给Son抽象类，发现Son中没有实现Copt则向Father发送消息SuperSendMsg就相当于事件响应链传递一样。一直向上传递直到能被处理。**这里需要注意一点Father中 Father * copyFather = [[self class]allocWithZone:zone];这里用的是self而不是Father因为Son会走到这里来，我们不能限制死到底是谁来调用***。接下来我们继续看为什么toy是个空置，这个原因和上面说的嵌套copy有点类似。因为Father不清楚你Son的属性到底是怎么copy过来的。那么怎么修改呢？我们只要在toy中稍作修改即可
```
 @implementation Son

 -(id)copyWithZone:(NSZone *)zone{

      //这句话保证父类的copy也被call到

     Son * son = [super copyWithZone:zone];

     son.toy   = [self.toy mutableCopy];

     return son;

 }

 @end
```
  Son
  输出结果：toy成功被深拷贝
  
  DataStruct[11606:2301994] sonA's toy Address = 0x100004288
  
  DataStruct[11606:2301994] sonB's toy Address = 0x656e6f68506965
- 接下来我们看一下第二种情况，父类没有实现NSCopying，子类如何实现NSCopying。直接让子类去实现就好了呗。父类如果需要深拷贝的我延迟到子类去执行呗！(这里有个问题，我的Son没有继承NSCopying，但是重写CopyWithZone居然没有报错？？！！)
```
 #import "Son.h"

 @implementation Son

 -(id)copyWithZone:(NSZone *)zone{

 //    Son * son = [super copyWithZone:zone];

     Son * son = [[self class] allocWithZone:zone];

     son.name  = [self.name mutableCopy];

     son.toy   = [self.toy mutableCopy];

     return son;

 }

 @end
```
  Son
  输出结果：
  
  DataStruct[11660:2317623] sonA's Address = 0x100206e00
  
  DataStruct[11660:2317623] sonB's Address = 0x1002040e0
  
  DataStruct[11660:2317623] sonA's name Address = 0x100004260
  
  DataStruct[11660:2317623] sonB's name Address = 0x726f6e6e6f6365
  
  DataStruct[11660:2317623] sonA's toy Address = 0x100004280
  
  DataStruct[11660:2317623] sonB's toy Address = 0x656e6f68506965

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