关于深复制与浅复制

转自“红黑联盟”，网址：http://www.2cto.com/kf/201405/302273.html

第一、复制对象的基本概念

复制一个对象为副本，开辟一块新的内存来存储副本对象。

第二、如果一个对象想具备复制的功能，必须实现协议和协议

NSObject自带的常用的对象有：NSNumber、NSString、NSArray、NSDictionary、NSMutableArray、NSMutableDictionay、NSMutableString，copy产生的对象时不可变的，mutableCopy产生的对象时可变的

第三、retain和copy的区别

    @autoreleasepool {
        NSMutableArray *array=[NSMutableArray arrayWithObjects:@"one",@"two",@"three",@"four",nil];
        NSMutableArray *retainArray=[array retain];
        [retainArray removeLastObject];
        for(NSString *str in array)
        {
            NSLog(@"the part is %@",str);
        }
        NSLog(@"the retaincount is %ld",[retainArray retainCount]);
        // insert code here...
        NSLog(@"Hello, World!");
        
    }

结果：

2014-05-19 10:58:22.639 objective[1095:303] the part is one
2014-05-19 10:58:22.641 objective[1095:303] the part is two
2014-05-19 10:58:22.641 objective[1095:303] the part is three
2014-05-19 10:58:22.641 objective[1095:303] the retaincount is 2

NSMutableArray *array=[NSMutableArray arrayWithObjects:@"one",@"two",@"three",@"four",nil];
        NSMutableArray *retainArray=[array mutableCopy];
        [retainArray removeLastObject];
        for(NSString *str in array)
        {
            NSLog(@"the part is %@",str);
        }
        NSLog(@"the retaincount is %ld",[retainArray retainCount]);

结果

2014-05-19 10:59:03.826 objective[1104:303] the part is one

2014-05-19 10:59:03.828 objective[1104:303] the part is two

2014-05-19 10:59:03.828 objective[1104:303] the part is three

2014-05-19 10:59:03.829 objective[1104:303] the part is four

2014-05-19 10:59:03.829 objective[1104:303] the retaincount is 1

第四、COPY和MutableCopy的区别

COPY 返回一个不可变对象的副本，MutalbeCopy返回一个可变对象的副本。

        NSArray *array=[NSArray arrayWithObjects:@"one",@"two", nil];
        NSMutableArray *array1=[array copy];
        [array1 addObject:@"three"];  //error
        NSMutableArray *array2=[array mutableCopy];
        [array2 addObject:@"three"];  //right
        // insert code here...
        NSLog(@"Hello, World!");

第五、浅copy和深copy

浅复制尽复制对象本身，对象里的属性、包含的对象不做复制

深复制复制全部，包括对象的属性和其他对象

Foundation框架支持复制的类，默认是浅复制

        NSMutableArray *array=[[NSMutableArray alloc] init];
        for(int i=0;i<3;i++)
        {
            NSObject *obj=[[NSObject alloc] init];
            [array addObject:obj];
            [obj release];
        }
        for(NSObject *obj1 in array)
        {
            NSLog(@"地址为 %p,引用计数是 %ld",obj1,obj1.retainCount);
        }
        NSMutableArray *array2=[array copy];
        for(NSObject *obj2 in array2)
        {
            NSLog(@"地址为 %p,引用计数是 %ld",obj2,obj2.retainCount);
        }

2013-09-30 17:28:01.492 FDAS[681:303] 地址为 0x1001081f0,引用计数是 1
2013-09-30 17:28:01.506 FDAS[681:303] 地址为 0x100108230,引用计数是 1
2013-09-30 17:28:01.506 FDAS[681:303] 地址为 0x100108240,引用计数是 1
2013-09-30 17:28:01.507 FDAS[681:303] 地址为 0x1001081f0,引用计数是 2
2013-09-30 17:28:01.507 FDAS[681:303] 地址为 0x100108230,引用计数是 2
2013-09-30 17:28:01.507 FDAS[681:303] 地址为 0x100108240,引用计数是 2

第五、对象的自定义拷贝

对象拥有复制特性，必须实现NSCopying，NSMutableCopying协议，实现该协议的copyWithZone方法和mutableCopyWithZone方法

深拷贝和浅拷贝的区别就在于copyWithZone方法的实现,

浅拷贝代码如下：

#import 

@interface Person : NSObject
@property(nonatomic,retain)NSString *name;
@property(nonatomic,retain)NSString *age;

@end

#import "Person.h"

@implementation Person

- (id)copyWithZone:(NSZone *)zone
{
   //实现自定义浅拷贝
    Person *person=[[self class] allocWithZone:zone];
    person.age=_age;
    person.name=_name;
    return person;
}
@end

main函数为：

    @autoreleasepool {
        
        Person *person=[[Person alloc] init];
        person.name=@"andy";
        person.age=@"20";
        
        Person *person2=[person copy];
        NSLog(@"person 地址为%p,person2地址为%p",person.name,person2.name);
    }

输出结果为：

2013-09-30 17:48:41.007 FDAS[732:303] person 地址为0x1000022c8,person2地址为0x1000022c8

深拷贝代码如下：

- (id)copyWithZone:(NSZone *)zone
{
   //实现自定义浅拷贝
    Person *person=[[self class] allocWithZone:zone];
    person.age=[_age copy];
    person.name=[_age copy];
    return person;
}

结果：

2013-09-30 17:55:13.603 FDAS[742:303] person 地址为0x1000022c8,person2地址为0x1000022e8

        NSArray *arr=[NSArray arrayWithObjects:@"one",@"two",nil];
        NSArray *arr2=[arr copy];
        NSLog(@"the dress of arr is %p the dress of arr2 is %p",arr,arr2);
        NSLog(@"the retainCount is %ld",arr.retainCount);

执行结果为：

2013-09-30 18:01:01.394 FDAS[787:303] the dress of arr is 0x100108320 the dress of arr2 is 0x100108320

2013-09-30 18:01:01.396 FDAS[787:303] the retainCount is 2

结果是一样的，是因为Foundation对于不可变复制对象而言，copy方法做了优化，相当于retain，故retaincount变成2.

相当于在copyWithZone方法中：return [self retain];

第六、copy、mutableCopy和retain之间的关系

在Foundation对象中，copy是一个不可变的对象时，作用相当于retain

当使用mutableCopy时，不管源对象是否可变，副本是可变的，并且实现真正意义上的copy

当我们使用copy一个可变对象时，副本对象是不可变的。

关于深拷贝和浅拷贝：

第一、浅拷贝：

    Car *car=[[[self class] allocWithZone:zone] init];
    car.engine=_engine;
    car.name=_name;
    car.weight=_weight;
    return car;

测试代码：

 Car *car = [[Car alloc] init];
        Engine *engine = [[Engine alloc] init];
        car.engine = engine;
        [engine release];
        //NSLog(@"engine retaincount is %lu",[engine retainCount]);
        car.name = @"奥迪";
        car.weight = @1000;

        Car *car2=[car copy];
       // NSLog(@"car2 retaincount is %lu",[car2 retainCount]);
        NSLog(@"car %@,car2:%@",car.engine,car2.engine);

输出结果：

car ,car2:

可以看出浅复制只是复制指针，并没有创建新的内存空间

第二、深拷贝：

- (id)copyWithZone:(NSZone *)zone {
    /***浅拷贝**/
    Car *car=[[[self class] allocWithZone:zone] init];
    Engine *engineCopy=[[_engine copy] autorelease];
    car.engine=engineCopy;
    
    NSString *namecopy=[[_name copy] autorelease];
    car.name=namecopy;
    
    NSNumber *weightcopy=[[_weight copy] autorelease];
    car.weight=weightcopy;
    return car;
}

测试代码：

Car *car = [[Car alloc] init];
        Engine *engine = [[Engine alloc] init];
        car.engine = engine;
        [engine release];
        //NSLog(@"engine retaincount is %lu",[engine retainCount]);
        car.name = @"奥迪";
        car.weight = @1000;

        Car *car2=[car copy];
       // NSLog(@"car2 retaincount is %lu",[car2 retainCount]);
        NSLog(@"car %@,car2:%@",car.engine,car2.engine);

结果：

car ,car2:

开辟了新的空间,zone代表一块内存空间

 Car *car=[[[self class] allocWithZone:zone] init];

注意上述代码用的是【self class】，而不是car，因为如果是用car，那么car的子类在调用此方法去实现copy协议时，就会出现内存问题

另外，当子类继承了父类时，他继承了父类的一切属性，包括要实现的协议

第三、NSFoundation，当我们copy的时一个不可变对象时，默认的copy都是浅拷贝,相当于retain

        NSArray *array =[NSArray arrayWithObjects:@"one",@"two",@"three", nil];
        NSArray *array1 = [array copy];
        NSLog(@"%p",array);
        NSLog(@"%p",array1);
        NSLog(@"the retaincount is %lu",[array retainCount]);

输出结果：

copyDemo1[673:303] 0x10010a5d0

2013-12-28 20:01:10.969 copyDemo1[673:303] 0x10010a5d0

2013-12-28 20:01:10.969 copyDemo1[673:303] the retaincount is 2

注意retaincount会增加

当使用mutableCopy时，不管对象是否可变，都会实现深拷贝

        NSArray *array =[NSArray arrayWithObjects:@"one",@"two",@"three", nil];
        NSMutableArray *array1 = [array mutableCopy];
        NSLog(@"%p",array);
        NSLog(@"%p",array1);
        NSLog(@"the retaincount is %lu",[array retainCount]);

结果：

copyDemo1[695:303] 0x10010a5d0

2013-12-28 20:07:08.570 copyDemo1[695:303] 0x10010b260

2013-12-28 20:07:08.570 copyDemo1[695:303] the retaincount is 1

第四、retain相当于两个对象指向同一个指针

        NSMutableArray *array1 = [[NSMutableArray alloc] initWithObjects:@"one",@"two",@"three",@"foure", nil];
        NSMutableArray *array2 = [array1 retain];
        [array2 removeLastObject];
        NSLog(@"%@",array1);
        NSLog(@"the retaincount is %ld",array2.retainCount);

结果：

2013-12-28 20:13:02.915 copyDemo1[736:303] (
    one,
    two,
    three
)
2013-12-28 20:13:02.917 copyDemo1[736:303] the retaincount is 2