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。