第二十五讲：Objective-C内存管理之浅拷贝

Sian

上一讲简述了拷贝的基本原理，这一讲以一个类进行说明浅拷贝的效果
1、创建一个类Car、使用<NSCopying>,<NSMutableCopying>协议对对象进行拷贝，自创的类必须实现拷贝中的 - (id)copyWithZone:(NSZone *)zone 方法或- (id)mutableCopyWithZone:(NSZone *)zone 方法；
2、修改拷贝对象中的值，这里区分copy与retain在对象操作中的不同点：car1 = car指向的是同一对象，car1 = [car copy]创建了另外一个对象，修改对象中的值不影响原来对象的值，但对象中的使用的其他对象不拷贝；
3、深拷贝则对对象引用的其他对象都进行拷贝（后续通过深拷贝说明）；
SACar.h

1. //
2. //  SACar.h
3. //  Copy
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, NSMutableCopying>
13. @property int year;
14. @property (copy) NSString *name;
16. @end

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SACar.m

1. //
2. //  SACar.m
3. //  Copy
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
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. }
20. - (id) mutableCopyWithZone:(NSZone *)zone {
21.     SACar * c = [[[[self class] allocWithZone:zone] init] autorelease];
22.     c.name = self.name;
23.     c.year = self.year;
24.     return c;
25. }
27. - (NSString *) description {
28.     return [NSString stringWithFormat:@"%@ age is %d", self.name, self.year];
29. }
31. - (void) dealloc {
32.     NSLog(@"%@ is dealloc", self.name);
33.     [super dealloc];
34. }
36. @end

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main.m

1. //
2. //  main.m
3. //  Copy
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.         
17.         SACar * car = [[[SACar alloc] init] autorelease];
18.         car.name = @"Cruze";
19.         car.year = 2013;
20.         NSLog(@"%@", car);
22.         SACar * car1 = [car copy];
23.         car1.name = @"Sonata";
24.         car1.year = 2014;
25.         NSLog(@"%@", car1);
26.         
27.         NSLog(@"%@ retainCount is %ld", car.name, car.retainCount);
28.         NSLog(@"%@ retainCount is %ld", car1.name, car1.retainCount);
29.         
30.         [car retain];
31.         NSLog(@"%@ retainCount is %ld", car.name, car.retainCount);
32.         NSLog(@"%@ retainCount is %ld", car1.name, car1.retainCount);
33.         [car release];
34.     }
35.     return 0;
36. }

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输出结果：

1. 2014-01-22 20:14:08.733 Copy[1788:303] Cruze age is 2013
2. 2014-01-22 20:14:08.735 Copy[1788:303] Sonata age is 2014
3. 2014-01-22 20:14:08.735 Copy[1788:303] Cruze retainCount is 1
4. 2014-01-22 20:14:08.735 Copy[1788:303] Sonata retainCount is 1
5. 2014-01-22 20:14:08.736 Copy[1788:303] Cruze retainCount is 2
6. 2014-01-22 20:14:08.736 Copy[1788:303] Sonata retainCount is 1
7. 2014-01-22 20:14:08.736 Copy[1788:303] Sonata is dealloc
8. 2014-01-22 20:14:08.737 Copy[1788:303] Cruze is dealloc
9. Program ended with exit code: 0

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Sian

如果将使用赋值，则效果如下：
main.m

1. //
2. //  main.m
3. //  Copy
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.         
17.         SACar * car = [[[SACar alloc] init] autorelease];
18.         car.name = @"Cruze";
19.         car.year = 2013;
20.         NSLog(@"%@", car);
22.         SACar * car1 =  car;
23.         car1.name = @"Sonata";
24.         car1.year = 2014;
25.         NSLog(@"%@", car1);
26.         NSLog(@"%@", car);
27.         
28.         NSLog(@"%@ retainCount is %ld", car.name, car.retainCount);
29.         NSLog(@"%@ retainCount is %ld", car1.name, car1.retainCount);
30.         
31.         [car retain];
32.         NSLog(@"%@ retainCount is %ld", car.name, car.retainCount);
33.         NSLog(@"%@ retainCount is %ld", car1.name, car1.retainCount);
34.         [car release];
35.     }
36.     return 0;
37. }

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输出结果为：

1. 2014-01-22 20:23:00.775 Copy[1885:303] Cruze age is 2013
2. 2014-01-22 20:23:00.776 Copy[1885:303] Sonata age is 2014
3. 2014-01-22 20:23:00.777 Copy[1885:303] Sonata age is 2014
4. 2014-01-22 20:23:00.777 Copy[1885:303] Sonata retainCount is 1
5. 2014-01-22 20:23:00.777 Copy[1885:303] Sonata retainCount is 1
6. 2014-01-22 20:23:00.777 Copy[1885:303] Sonata retainCount is 2
7. 2014-01-22 20:23:00.778 Copy[1885:303] Sonata retainCount is 2
8. 2014-01-22 20:23:00.778 Copy[1885:303] Sonata is dealloc
9. Program ended with exit code: 0

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