IOS中复制对象的用法及深拷贝和浅拷贝详解
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