-
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
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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;
}
@endCar
/** .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;
}
@endFather
#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
@endSon
#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;
}
@endSon
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;
}
@endSon
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
- 下面我们定义一个Father类，来实现深拷贝：