oc为每个对象提供一个内部计数器，这个计数器跟踪对象的引用计数，当对象被创建或拷贝时，引用计数为1，每次保持对象时，调用retain接口，引用计数加1，如果不需要这个对象时调用release，引用计数减1，当对像的引用计数为0时，系统就会释放掉这块内存,释放对象调用dealloc

当对象包含其他对象时，就得在dealloc中自己释放他们

有两个基本函数，alloc和dealloc

alloc类似于C++的new，dealloc类似于delete

当对象的retaincount为0时，自动调用dealloc函数

release只是使retaincount-1，不是调用dealloc函数

内存管理的原则：

如果使用alloc，copy创建的对象，一定要release

如果你retain一个对象，那么必须要release

Song 类的实现

#import

@interface Song : NSObject
{
NSString *_title;
NSString *_artist;
long int _duration;
}
@property (nonatomic,retain) NSString *title;
@property (nonatomic,retain) NSString *artist;
@property (nonatomic,assign) long int duration;
-(Song*)initwithTitle:(NSString *)t AndArtist:(NSString *)art AndDuration:(long int)d;
@end

#import "Song.h"

@implementation Song
@synthesize title=_title;
@synthesize artist=_artist;
@synthesize duration=_duration;

-(Song*)initwithTitle:(NSString *)t AndArtist:(NSString *)art AndDuration:(long)d
{
self=[super init];
if(self)
{
self.title=t;
self.artist=art;
self.duration=d;
}
return self;
}
@end
main函数code

int main(int argc, const char * argv[])
{

Song *Song1=[[Song alloc] initwithTitle:@"what" AndArtist:@"hello" AndDuration:3];
Song *Song2=[[Song alloc] initwithTitle:@"aaa" AndArtist:@"bbb" AndDuration:4];
NSLog(@"Song1 retain count is %ld",[Song1 retainCount]);
NSLog(@"Song2 retain count is %ld",[Song2 retainCount]);
[Song1 retain];
[Song2 retain];
NSLog(@"Song1 retain count is %ld",[Song1 retainCount]);
NSLog(@"Song2 retain count is %ld",[Song2 retainCount]);
[Song1 release];
[Song2 release];
NSLog(@"Song1 retain count is %ld",[Song1 retainCount]);
NSLog(@"Song2 retain count is %ld",[Song2 retainCount]);
[Song1 release];
[Song2 release];
return 0;
}

the result：

2013-05-07 14:44:55.170 Access[2891:303] Song1 retain count is 1
2013-05-07 14:44:55.173 Access[2891:303] Song2 retain count is 1
2013-05-07 14:44:55.173 Access[2891:303] Song1 retain count is 2
2013-05-07 14:44:55.173 Access[2891:303] Song2 retain count is 2
2013-05-07 14:44:55.174 Access[2891:303] Song1 retain count is 1
2013-05-07 14:44:55.174 Access[2891:303] Song2 retain count is 1

内存管理释放池提供了一个对象容器，每次对象发送autorelease时，对象的引用计数并不真正变化，而是内存释放池记录一条记录，记下该对象的要求，直到内存释放池发送retain或release时，当池在销毁之前通知池内所有元素，发送release消息减1，这部分代码必须放在:

NSAutoreleasePool *pool=[[NSAutoreleasePool alloc]init];

和 [pool release]; 之间

int main(int argc, const char * argv[])
{

NSAutoreleasePool *pool=[[NSAutoreleasePool alloc]init];
NSArray *weeks1=[NSArray arrayWithObjects:@"monday",@"tuesday",@"thursday", nil];
NSArray *weeks2=[[NSArray alloc ]initWithObjects:@"monday",@"tuesday",@"thursday", nil];
//[weeks1 autorelease];
[weeks1 release];
[weeks2 release];
//[weeks2 autorelease];

NSLog(@"retain count is %ld",[weeks1 retainCount]);
NSLog(@"retain count is %ld",[weeks2 retainCount]);
[pool release];
return 0;
}

属性简介

@property 和@synthesize 可以自动生成某个类成员变量的存取方法，

语法 @property(参数) 类型 名字

这里的参数分为三大类：

读写属性：（readwrite/readonly） readwrite：这个属性是默认的，readonly：只生成getter 不会有setter

原子性（nonatomic）atomic ；是为了保证程序能够并发，避免同步问题

assign：这个属性用来处理基础类型，比如int，float，如果你声明的类型就是基础类型，该属性可以不加

对于assign而言，set函数和get函数如下所示：

@property(nonatomic,assign)int val;

-(int)val

{

return val;

}

(void)setVal:(int)newVal