OC MRC之多对象之间管理（代码分析）

 #import <Foundation/Foundation.h>

 @interface Book : NSObject
 {
     int _price;
 }

 - (void)setPrice:(int)price;
 - (int)price;

 @end

 #import "Book.h"

 @implementation Book

 - (void)setPrice:(int)price
 {
     _price = price;
 }

 - (int)price
 {
     return _price;
 }
 - (void)dealloc
 {
     NSLog(@"Book对象被回收");
     [super dealloc];
 }
 @end

 #import <Foundation/Foundation.h>
 #import "Book.h"

 @interface Person : NSObject
 {
     Book *_book;
 }

 - (void)setBook:(Book *)book;
 - (Book *)book;

 @end

 #import "Person.h"

 @implementation Person
 - (void)setBook:(Book *)book
 {
     _book = [book retain];
 }

 - (Book *)book
 {
     return _book;
 }

 - (void)dealloc
 {
     [_book release];
     NSLog(@"Person对象被回收");
     [super dealloc];
 }
 @end

 /*
  1.你想使用（占用）某个对象，就应该让对象的计数器+1（让对象做一次retain操作）
  2.你不想再使用（占用）某个对象，就应该让对象的计数器-1（让对象做一次release）

  3.谁retain，谁release

  4.谁alloc，谁release
  */

 #import <Foundation/Foundation.h>
 #import "Person.h"
 #import "Book.h"

 int main()
 {
     // b-1
     Book *b = [[Book alloc] init];
     // p-1
     Person *p1 = [[Person alloc] init];

     //p1想占用b这本书
     // b-2
     [p1 setBook:b];

     // p-0
     // b-1
     [p1 release];
     p1 = nil;

     // b-0
     [b release];
     b = nil;
     return ;
 }