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

 //  Book.h

 //  引用计数器

 //

 //  Created by ma c on 15/8/13.

 //  Copyright (c) 2015年. All rights reserved.

 //

 #import <Foundation/Foundation.h>

 @interface Book : NSObject

 {

     NSString *_title;

     NSString *_author;

     CGFloat _price;

 }

 -(id)initWithTitle:(NSString*)title andAuthor:(NSString*)author

             AndPrice:(CGFloat)price;

 -(void)setTitle:(NSString*) title;

 -(void)setAuthor:(NSString*) author;

 -(void)setPrice:(CGFloat) price;

 -(NSString*) title;

 -(NSString*) author;

 -(CGFloat) price;

 -(void) show;

 @end

　　　　　　.m声明文件

 //  Book.m

 //  引用计数器

 //

 //  Created by ma c on 15/8/13.

 //  Copyright (c) 2015年. All rights reserved.

 //

 #import "Book.h"

 @implementation Book

 -(id)initWithTitle:(NSString*)title andAuthor:(NSString*)author

             AndPrice:(CGFloat)price

 {

     self = [super init];

     if(self)

     {

         _title = [title retain];

         _author = [author retain];

         _price = price;

     }

     return self;

 }

 -(void)setTitle:(NSString*) title

 {

     if(_title != title)

     {

       [_title release];//释放上一次拥有的对象所有权

       _title = [title retain];//获取这一次的对象所有权

     }

 }

 -(void)setAuthor:(NSString*) author

 {

     if(_author != author)

     {

       [_author release];//释放上一次拥有的对象所有权

       _author = [author retain];//获取这一次的对象所有权

     }

 }

 -(void)setPrice:(CGFloat) price

 {

     _price = price;

 }

 -(NSString*) title

 {

     return _title;

 }

 -(NSString*) author

 {

     return _author;

 }

 -(CGFloat) price

 {

     return _price;

 }

 -(void) show

 {

     NSLog(@"title:%@,author:%@,price:%.2f",_title,_author,_price);

 }

 -(void)dealloc

 {

     [_title release];

     [_author release];

     NSLog(@"title retainCount:0");

     NSLog(@"author retainCount:0");

     NSLog(@"book retainCount:0");

     NSLog(@"book is dealloc!");

     [super dealloc];

 }

 @end

　　　　测试Book类

 //  main.m

 //  引用计数器

 //

 //  Created by ma c on 15/8/13.

 //  Copyright (c) 2015年. All rights reserved.

 //

 #import <Foundation/Foundation.h>

 #import "Book.h"

 int main(int argc, const char * argv[])

 {

     //@autoreleasepool {

         //创建书对象book并初始化

         Book *book = [[Book alloc]initWithTitle:@"OC" andAuthor:@"Jobs" AndPrice:35.6];//book count:1

         NSLog(@"book retainCount:%lu",[book retainCount]);

         //创建书名对象title

         NSMutableString *title = [NSMutableString stringWithString:@"IOS"];//title count:1

         NSLog(@"title retainCount:%lu",[title retainCount]);

         //设置书名

         [book setTitle: title];//title count:2

         NSLog(@"title retainCount:%lu",[title retainCount]);

         //创建书的作者对象author

         NSMutableString *author = [NSMutableString stringWithString:@"Bill"];//author count:1

         NSLog(@"author retainCount:%lu",[author retainCount]);

         //设置书的作者名

         [book setAuthor:author];//author count:2

         NSLog(@"author retainCount:%lu",[author retainCount]);

         //设置书的价格

         [book setPrice:58.9];

         //释放title对象所有权----与上面的创建title对象相对应

         [title release];//title count:1

         NSLog(@"title retainCount:%lu",[title retainCount]);

         //释放author对象所有权----与上面的创建author对象相对应

         [author release];//author count:1

         NSLog(@"author retainCount:%lu",[author retainCount]);

         //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

         [book show];

         [book release];//title count:0, author count:0 ,book count:0, dealloc book

     //}

     return ;

 }

　　　　运行结果：

-- ::49.608 引用计数器[:] book retainCount:

-- ::49.609 引用计数器[:] title retainCount:

-- ::49.610 引用计数器[:] title retainCount:

-- ::49.610 引用计数器[:] author retainCount:

-- ::49.610 引用计数器[:] author retainCount:

-- ::49.610 引用计数器[:] title retainCount:

-- ::49.610 引用计数器[:] author retainCount:

-- ::49.610 引用计数器[:] title:IOS,author:Bill,price:58.90

-- ::49.611 引用计数器[:] title retainCount:

-- ::49.611 引用计数器[:] author retainCount:

-- ::49.611 引用计数器[:] book retainCount:

-- ::49.611 引用计数器[:] book is dealloc!

Program ended with exit code:

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。

巴特西

Objective-C:MRC手动释放对象内存举例(引用计数器)

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