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 0;
}

　　　　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。