Objective-C:MRC手动释放对象内存举例(引用计数器)

手机内存下的类的设计练习：

设计Book类，

1.三个成员变量：

title(书名）author(作者)、price(价格)

2.不使用@property,自己完成存取方法(set方法,get方法)

3、加入必要其他的方法

4、并对Book类进行测试

　　　　.h声明文件

 1 //  Book.h
 2 //  引用计数器
 3 //
 4 //  Created by ma c on 15/8/13.
 5 //  Copyright (c) 2015年 bjsxt. All rights reserved.
 6 //
 7
 8 #import <Foundation/Foundation.h>
 9
10 @interface Book : NSObject
11 {
12     NSString *_title;
13     NSString *_author;
14     CGFloat _price;
15 }
16 -(id)initWithTitle:(NSString*)title andAuthor:(NSString*)author
17             AndPrice:(CGFloat)price;
18 -(void)setTitle:(NSString*) title;
19 -(void)setAuthor:(NSString*) author;
20 -(void)setPrice:(CGFloat) price;
21 -(NSString*) title;
22 -(NSString*) author;
23 -(CGFloat) price;
24 -(void) show;
25 @end

　　　　　　.m声明文件

 1 //  Book.m
 2 //  引用计数器
 3 //
 4 //  Created by ma c on 15/8/13.
 5 //  Copyright (c) 2015年 bjsxt. All rights reserved.
 6 //
 7
 8 #import "Book.h"
 9
10 @implementation Book
11 -(id)initWithTitle:(NSString*)title andAuthor:(NSString*)author
12             AndPrice:(CGFloat)price
13 {
14     self = [super init];
15     if(self)
16     {
17         _title = [title retain];
18         _author = [author retain];
19         _price = price;
20     }
21     return self;
22 }
23 -(void)setTitle:(NSString*) title
24 {
25     if(_title != title)
26     {
27       [_title release];//释放上一次拥有的对象所有权
28       _title = [title retain];//获取这一次的对象所有权
29     }
30 }
31 -(void)setAuthor:(NSString*) author
32 {
33     if(_author != author)
34     {
35       [_author release];//释放上一次拥有的对象所有权
36       _author = [author retain];//获取这一次的对象所有权
37     }
38 }
39 -(void)setPrice:(CGFloat) price
40 {
41     _price = price;
42 }
43 -(NSString*) title
44 {
45     return _title;
46 }
47 -(NSString*) author
48 {
49     return _author;
50 }
51 -(CGFloat) price
52 {
53     return _price;
54 }
55 -(void) show
56 {
57     NSLog(@"title:%@,author:%@,price:%.2f",_title,_author,_price);
58 }
59 -(void)dealloc
60 {
61     [_title release];
62     [_author release];
63     NSLog(@"title retainCount:0");
64     NSLog(@"author retainCount:0");
65     NSLog(@"book retainCount:0");
66     NSLog(@"book is dealloc!");
67     [super dealloc];
68 }
69 @end

　　　　测试Book类

 1 //  main.m
 2 //  引用计数器
 3 //
 4 //  Created by ma c on 15/8/13.
 5 //  Copyright (c) 2015年 bjsxt. All rights reserved.
 6 //
 7
 8 #import <Foundation/Foundation.h>
 9 #import "Book.h"
10 int main(int argc, const char * argv[])
11 {
12     //@autoreleasepool {
13
14         //创建书对象book并初始化
15         Book *book = [[Book alloc]initWithTitle:@"OC" andAuthor:@"Jobs" AndPrice:35.6];//book count:1
16         NSLog(@"book retainCount:%lu",[book retainCount]);
17
18         //创建书名对象title
19         NSMutableString *title = [NSMutableString stringWithString:@"IOS"];//title count:1
20         NSLog(@"title retainCount:%lu",[title retainCount]);
21
22         //设置书名
23         [book setTitle: title];//title count:2
24         NSLog(@"title retainCount:%lu",[title retainCount]);
25
26         //创建书的作者对象author
27         NSMutableString *author = [NSMutableString stringWithString:@"Bill"];//author count:1
28         NSLog(@"author retainCount:%lu",[author retainCount]);
29
30         //设置书的作者名
31         [book setAuthor:author];//author count:2
32         NSLog(@"author retainCount:%lu",[author retainCount]);
33
34
35         //设置书的价格
36         [book setPrice:58.9];
37
38
39         //释放title对象所有权----与上面的创建title对象相对应
40         [title release];//title count:1
41         NSLog(@"title retainCount:%lu",[title retainCount]);
42
43         //释放author对象所有权----与上面的创建author对象相对应
44         [author release];//author count:1
45         NSLog(@"author retainCount:%lu",[author retainCount]);
46
47
48         //释放在book类中的成员实例变量title和author对象的所有权，并销毁book对象
49         [book show];
50         [book release];//title count:0, author count:0 ,book count:0, dealloc book
51     //}
52     return 0;
53 }

　　　　运行结果：

2015-08-13 16:56:49.608 引用计数器[1527:94167] book retainCount:1
2015-08-13 16:56:49.609 引用计数器[1527:94167] title retainCount:1
2015-08-13 16:56:49.610 引用计数器[1527:94167] title retainCount:2
2015-08-13 16:56:49.610 引用计数器[1527:94167] author retainCount:1
2015-08-13 16:56:49.610 引用计数器[1527:94167] author retainCount:2
2015-08-13 16:56:49.610 引用计数器[1527:94167] title retainCount:1
2015-08-13 16:56:49.610 引用计数器[1527:94167] author retainCount:1
2015-08-13 16:56:49.610 引用计数器[1527:94167] title:IOS,author:Bill,price:58.90
2015-08-13 16:56:49.611 引用计数器[1527:94167] title retainCount:0
2015-08-13 16:56:49.611 引用计数器[1527:94167] author retainCount:0
2015-08-13 16:56:49.611 引用计数器[1527:94167] book retainCount:0
2015-08-13 16:56:49.611 引用计数器[1527:94167] book is dealloc!
Program ended with exit code: 0

可以看出:

计数器：retainCount

对象中存储被引用的次数，

当被引用的时候，计数器加1；

不在引用的时候，计数器减1；

当计数器为0的时候，真正去销毁对象。