第二十六讲：Objective-C内存管理之深拷贝

Sian

继续上一讲的浅拷贝，深拷贝的区别在于是否拷贝对象中的引用对象1、创建一个数组array，将类Car创建三个对象并保存到数组array中，使用[[NSMutableArray alloc] initWithArray:array]方法将array数组拷贝到array1中，修改array中的car元素，查看array1中的car是否发生变化；
2、使用[[NSMutableArray alloc] initWithArray:array copyItems:YES]方法将array拷贝到array2中，修改array中的car元素，查看array2中的car是否发生变化；
SACar.h

1. //
2. //  SACar.h
3. //  DeepCopy
4. //
5. //  Created by yusian on 14-1-22.
6. //  Copyright (c) 2014年 yusian. All rights reserved.
7. //
9. #import <Foundation/Foundation.h>
11. @interface SACar : NSObject <NSCopying>
13. @property (assign) NSString * name;
14. @property int year;
16. @end

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SACar.m

1. //
2. //  SACar.m
3. //  DeepCopy
4. //
5. //  Created by yusian on 14-1-22.
6. //  Copyright (c) 2014年 yusian. All rights reserved.
7. //
9. #import "SACar.h"
11. @implementation SACar
12. //***************************************NSCopying
13. - (id) copyWithZone:(NSZone *)zone {
14.     SACar * c = [[[[self class] allocWithZone:zone] init] autorelease];
15.     c.name = self.name;
16.     c.year = self.year;
17.     return c;
18. }
19. //***************************************NSCopying_end
21. - (NSString *) description {
22.     return [NSString stringWithFormat:@"%@ age is %d", self.name, self.year];
23. }
25. - (void) dealloc {
26.     NSLog(@"%@ is dealloc", self.name);
27.     self.name = nil;
28.     [super dealloc];
29. }
31. @end

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main.m

1. //
2. //  main.m
3. //  DeepCopy
4. //
5. //  Created by yusian on 14-1-22.
6. //  Copyright (c) 2014年 yusian. All rights reserved.
7. //
9. #import <Foundation/Foundation.h>
10. #import "SACar.h"
12. int main(int argc, const char * argv[])
13. {
15.     @autoreleasepool {
16.         NSMutableArray * array = [[NSMutableArray alloc] init];
17.         
18.         for (int i = 0; i < 3; i ++) {
19.             SACar * car = [[SACar alloc] init];
20.             car.name = [NSString stringWithFormat:@"Car%d", i];
21.             car.year = 2000 + i;
22.             [array addObject:car];
23.             [car release];
24.         }
25.         NSLog(@"%@", array);
26.         
27.         NSMutableArray * array1 = [[NSMutableArray alloc] initWithArray:array];
28.         [[array1 objectAtIndex:0] setName:@"NewCar"];
29.         NSLog(@"%@", array);
30.         
31.         NSMutableArray * array2 = [[NSMutableArray alloc] initWithArray:array copyItems:YES];
32.         [[array2 objectAtIndex:0] setName:@"SecondCar"];
33.         NSLog(@"%@", array);
34.         NSLog(@"%@", array2);
35.         
37. //        [array release];
38. //        [array1 release];
39. //        [array2 release];
40.     }
41.     return 0;
42. }

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运行结果：

1. 2014-01-22 21:40:09.327 DeepCopy[2643:303] (
2.     "Car0 age is 2000",
3.     "Car1 age is 2001",
4.     "Car2 age is 2002"
5. )
6. 2014-01-22 21:40:09.329 DeepCopy[2643:303] (
7.     "NewCar age is 2000",
8.     "Car1 age is 2001",
9.     "Car2 age is 2002"
10. )
11. 2014-01-22 21:40:09.329 DeepCopy[2643:303] (
12.     "NewCar age is 2000",
13.     "Car1 age is 2001",
14.     "Car2 age is 2002"
15. )
16. 2014-01-22 21:40:09.329 DeepCopy[2643:303] (
17.     "SecondCar age is 2000",
18.     "Car1 age is 2001",
19.     "Car2 age is 2002"
20. )
21. 2014-01-22 21:40:09.330 DeepCopy[2643:303] Car2 is dealloc
22. 2014-01-22 21:40:09.330 DeepCopy[2643:303] Car1 is dealloc
23. 2014-01-22 21:40:09.330 DeepCopy[2643:303] SecondCar is dealloc
24. Program ended with exit code: 0

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结果表示：
进行浅拷贝后，修改array中的Car0为“NewCar”后，array与array1中的Car0都变成了NewCar；
进行深拷贝后，修改array2中的Car0为“SecondCar”后，array中的Car0依然为之前的NewCar；
array2打印出来的结果中，Car0被修改成SecondCar，并且array2被自动释放，array与array1却没有，为什么？

Sian

深拷贝还可以通过归档的方式来实现：
1、创建好的数组array归档到data中；
2、将data解档到array1中，该过程会将归档的数据读出重新加载到数组array1中；
3、需要注意的是：前面使用数组的copy方法，Car中的Name属性为assign，使用数组copy后会自动内存管理，但通过归档方式实现，解档时会报错，因此，在声明属性时，需要使用copy属性：@property(copy) NSString * name;
代码如下：
SACar.h

1. //
2. //  SACar.h
3. //  DeepCopy
4. //
5. //  Created by yusian on 14-1-22.
6. //  Copyright (c) 2014年 yusian. All rights reserved.
7. //
9. #import <Foundation/Foundation.h>
11. @interface SACar : NSObject <NSCopying, NSCoding>
13. @property (copy) NSString * name;
14. @property int year;
16. @end

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SACar.m

1. //
2. //  SACar.m
3. //  DeepCopy
4. //
5. //  Created by yusian on 14-1-22.
6. //  Copyright (c) 2014年 yusian. All rights reserved.
7. //
9. #import "SACar.h"
11. @implementation SACar
12. //***************************************NSCopying
13. - (id) copyWithZone:(NSZone *)zone {
14.     SACar * c = [[[[self class] allocWithZone:zone] init] autorelease];
15.     c.name = self.name;
16.     c.year = self.year;
17.     return c;
18. }
19. //***************************************NSCopying_end
21. //***************************************NSCoding
22. - (void) encodeWithCoder:(NSCoder *)aCoder {
23.     [aCoder encodeObject:self.name forKey:@"Name"];
24.     [aCoder encodeInt:self.year forKey:@"Year"];
25. }
28. - (id) initWithCoder:(NSCoder *)aDecoder {
29.     if (self = [super init]) {
30.         self.name = [aDecoder decodeObjectForKey:@"Name"];
31.         self.year = [aDecoder decodeIntForKey:@"Year"];
32.     }
33.     return self;
34. }
35. //***************************************NSCoding_end
37. - (NSString *) description {
38.     return [NSString stringWithFormat:@"%@ age is %d", self.name, self.year];
39. }
41. - (void) dealloc {
42.     NSLog(@"%@ is dealloc", self.name);
43.     self.name = nil;
44.     [super dealloc];
45. }
47. @end

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main.m

1. //
2. //  main.m
3. //  DeepCopy
4. //
5. //  Created by yusian on 14-1-22.
6. //  Copyright (c) 2014年 yusian. All rights reserved.
7. //
9. #import <Foundation/Foundation.h>
10. #import "SACar.h"
12. int main(int argc, const char * argv[])
13. {
14.    
15.     @autoreleasepool {
16.         NSMutableArray * array = [[NSMutableArray alloc] init];
17.         
18.         for (int i = 0; i < 3; i ++) {
19.             SACar * car = [[SACar alloc] init];
20.             car.name = [NSString stringWithFormat:@"Car%d", i];
21.             car.year = 2000 + i;
22.             [array addObject:car];
23.             [car release];
24.         }
25.         NSLog(@"%@", array);
26.         
27.         NSData * data = [NSKeyedArchiver archivedDataWithRootObject:array];
28.         NSMutableArray * array1 = [NSKeyedUnarchiver unarchiveObjectWithData:data];
29.         [[array1 objectAtIndex:0] setName:@"NewCar"];
30.         NSLog(@"%@", array);
31.         
32.         [array release];
33.         //[array1 release];
34.    
35.     }
36.     return 0;
37. }

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输出结果：

1. 2014-01-22 22:46:06.956 DeepCopy[3316:303] (
2.     "Car0 age is 2000",
3.     "Car1 age is 2001",
4.     "Car2 age is 2002"
5. )
6. 2014-01-22 22:46:06.958 DeepCopy[3316:303] (
7.     "Car0 age is 2000",
8.     "Car1 age is 2001",
9.     "Car2 age is 2002"
10. )
11. 2014-01-22 22:46:06.958 DeepCopy[3316:303] Car0 is dealloc
12. 2014-01-22 22:46:06.959 DeepCopy[3316:303] Car1 is dealloc
13. 2014-01-22 22:46:06.959 DeepCopy[3316:303] Car2 is dealloc
14. 2014-01-22 22:46:06.959 DeepCopy[3316:303] NewCar is dealloc
15. 2014-01-22 22:46:06.960 DeepCopy[3316:303] Car1 is dealloc
16. 2014-01-22 22:46:06.960 DeepCopy[3316:303] Car2 is dealloc
17. Program ended with exit code: 0

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同样的道理，通过归档进行深拷贝的对象不需要release，这与@autoreleasepool有关系，原因暂未知；