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标题: 二战黑马：循环引用、类的提前声明 [打印本页]
作者: 崔石炫    时间: 2014-10-23 23:59
标题: 二战黑马：循环引用、类的提前声明
  1. //  Person.h
  2. #import <Foundation/Foundation.h>

  4. @class Dog , Card; //@class关键字提前声明两个类，提高性能

  6. @interface Person : NSObject

  8. @property(nonatomic , retain) Dog *dog;
  9. @property(nonatomic , retain) Card *card;

  11. @end
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  1. //  Person.m
  2. #import "Person.h"
  3. #import "Dog.h" //.m文件中正式import头文件
  4. #import "Card.h"

  6. @implementation Person

  8. - (void)dealloc
  9. {
  10.     NSLog(@"Person被回收");
  11.     [_dog release]; //retain修饰的属性要进行release操作
  12.     [_card release];
  13.     [super dealloc];
  14. }

  16. @end
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  1. //  Dog.h
  2. #import <Foundation/Foundation.h>
  3. #import "Person.h"

  5. @class Person;

  7. @interface Dog : NSObject

  9. @property(nonatomic , assign) Person *owner;

  11. @end
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  1. //  Dog.m
  2. #import "Dog.h"
  3. #import "Person.h"

  5. @implementation Dog

  7. - (void)dealloc
  8. {
  9.     NSLog(@"Dog被回收"); //assign修饰的_owner不需要进行release操作
  10.     [super dealloc];
  11. }

  13. @end
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  1. //  Card.h
  2. #import <Foundation/Foundation.h>
  3. #import "Person.h"

  5. @class Person;

  7. @interface Card : NSObject

  9. @property(nonatomic , assign) Person *owner;

  11. @end
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  1. //  Card.m
  2. #import "Card.h"
  3. #import "Person.h"

  5. @implementation Card

  7. - (void)dealloc
  8. {
  9.     NSLog(@"Card被回收"); //assign修饰的_owner不需要进行release操作
  10.     [super dealloc];
  11. }

  13. @end
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  1. //  main.m
  2. #import <Foundation/Foundation.h>
  3. #import "Dog.h"
  4. #import "Card.h"
  5. #import "Person.h"

  7. /*
  8. 类的循环引用：你中有我，我中有你
  9. * 要使用@class在.h文件中提前声明所应用的类，然后在.m中#import头文件
  10. *解决办法：一端用retain，另一端用assign
  11. */

  13. int main(int argc, const char * argv[])
  14. {
  15.     Person *p1 = [[Person alloc] init];
  16.     Person *p2 = [[Person alloc] init];
  17.    
  18.     Dog *d1 = [[Dog alloc] init];
  19.     Dog *d2 = [[Dog alloc] init];
  20.    
  21.     Card *c1 = [[Card alloc] init];
  22.     Card *c2 = [[Card alloc] init];
  23.    
  24.     p1.dog = d1;
  25.     d1.owner = p1;
  26.     p1.card = c1;
  27.     c1.owner = p1;
  28.    
  29.     p2.dog = d2;
  30.     d2.owner = p2;
  31.     p2.card = c2;
  32.     c2.owner = p2;
  33.    
  34.     //两个人交换dog 和 card
  35.     p1.dog = d2;
  36.     d2.owner = p1;
  37.     p1.card = c2;
  38.     c2.owner = p1;
  39.    
  40.     p2.dog = d1;
  41.     d1.owner = p2;
  42.     p2.card = c1;
  43.     c1.owner = p2;
  44.    
  45.     [p1 release];
  46.     [p2 release];
  47.     [d1 release];
  48.     [d2 release];
  49.     [c1 release];
  50.     [c2 release];
  51.    
  52.     return 0;
  53. }
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