ios学习笔记之OC篇(二)：引用计数

例题：已知存在属性@property (nonatomic,retain) NSArray *arr;该属性自动生成的set方法代码为：
-(void) setArr:(NSArray *)arr
{
     _arr=arr;
     [_arr retain];
}
[b]示例1：[/b]
@property (nonatomic,retain) Person *friend;

Person *p=nil;

    @autoreleasepool {

       

        //没有添加进自动释放池时，自动释放池对其无影响

        p=[[[Person alloc]init]autorelease];//+1假如没有autorelease最后一个retainCount仍保持2，不会-1

        Person *p1=p;//不变

        NSLog(@"%ld",[p retainCount]);
//        Person *p2=[p copy];//p的引用计数不+1
//        NSLog(@"%ld",[p retainCount]);

        Person *p3=[[Person alloc]init];

        p3.friend=p;//p的引用计数+1

        NSLog(@"%ld",[p retainCount]);

       

        NSLog(@"Hello,
World!");

       

    }//p的引用计数-1

    NSLog(@"%ld",[p retainCount]);

示例2：常量没有引用计数机制，因为永远不能释放这些对象：NSNumber,NSString...也同样适用于使用常量字符串初始化的不可变字符串对象
@autoreleasepool {
//        NSNumber *myInt=[NSNumber numberWithInt:100];  //+1
//        NSNumber *myInt1;  //用NSNumber显示不正确

        Person *myInt=[[Person alloc]init];

        Person *myInt1;

        NSMutableArray *myArr=[NSMutableArray array];

       

        NSLog(@"myInt
retainCount is %ld",[myInt retainCount]);//1

        [myArr addObject:myInt];

        NSLog(@"after
add to array ,myInt retainCount is %ld",(unsigned long)[myInt retainCount]);//2

        myInt1=myInt;

        NSLog(@"after
assign to myInt1 ,myInt retainCount is %ld",(unsigned long)[myInt retainCount]);//2

        [myInt retain];

        NSLog(@"after
retain ,myInt retainCount is %ld",(unsigned long)[myInt retainCount]);//3

        NSLog(@"after
retain ,myInt1 retainCount is %ld",(unsigned long)[myInt1 retainCount]);//3

        [myInt release];

        NSLog(@"after
release ,myInt retainCount is %ld",(unsigned long)[myInt retainCount]);//2

        [myArr removeObjectAtIndex:0];

        NSLog(@"after
remove from array,myInt retainCount is %ld",(unsigned long)[myInt retainCount]);//1

    }

示例3：引用计数与实例变量
-(void)setName:(NSString *)_name

{

    name=_name;

}

-(NSString *)name

{

    return name;

}

NSMutableString *str3=[NSMutableString stringWithString:@"string
3"];

        Person *person
=[[Person alloc]init];

        NSLog(@"str3
retainCount is %ld",[str3 retainCount]);//1

        [person setName:str3];

        NSLog(@"after
assign to name ,str3 retainCount is %ld",[str3 retainCount]);//1

ps:假如setName方法的实现为：name=_name;[name retain];则str3的retainCount会+1。