pragma mark @class第二个应用场景

pragma mark 概念

/**

 两个类相互引用,你拷贝我,我拷贝你,出现循环引用
 
 */

pragma mark 代码

#import <Foundation/Foundation.h>
#pragma mark 类
#import "Person.h"
#pragma mark main函数
int main(int argc, const char * argv[])
{
    
    Person *p = [Person new];
    Dog *d = [Dog new];
    
    p.dog = d;
    
    [p release];
    [d release];
    
    return 0;
}

Person.h //人类

#import <Foundation/Foundation.h>
//#import "Dog.h"
/**
 #import "Dog.h"
 相当于
 #import <Foundation/Foundation.h>
 #import "Person.h"
 @interface Dog : NSObject
 @property(nonatomic, retain)Person *owner;
 @end
 */

@class Dog;
/**
 总结: 如果两个类相互拷贝,例如A拷贝B,B拷贝A,这样会保存
 如果解决:在.m中使用class,在.m中用import
 因为如果.h中都没用#import, 例如A拷贝B,B拷贝A,会形成死循环
 
 如果在.h@class,不会做任何拷贝操作,在.m中import 只会拷贝对应的文件,并不会形成死循环
 */
@interface Person : NSObject

@property(nonatomic, retain)Dog *dog;

@end

Person.m

#import "Person.h"
#import "Dog.h"

@implementation Person

- (void)dealloc
{
    NSLog(@"%s",__func__);
    [_dog release];
    [super dealloc];
    
}
@end

Dog.h //狗类

#import <Foundation/Foundation.h>
//#import "Person.h"
@class Person;

// #import "Person.h"
// 相当于
//#import <Foundation/Foundation.h>
//#import "Person.h"
//@interface Dog : NSObject
//@property(nonatomic, retain)Person *owner;
//@end

//@interface Person : NSObject
//
//@property(nonatomic, retain)Dog *dog;
//
//@end

@interface Dog : NSObject

@property(nonatomic, retain)Person *owner;


@end

Dog.m

#import "Dog.h"
#import "Person.h"
@implementation Dog

- (void)dealloc
{
    [_owner release];
    NSLog(@"%s",__func__);
    [super dealloc];
}
@end