oc为每一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。假设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
当对象包括其它对象时，就得在dealloc中自己释放他们
NSObject是IOS全部类的基类有两个基本函数。alloc和dealloc
alloc相似于C++的new。dealloc相似于delete
当对象的retaincount为0时。自己主动调用dealloc函数
release仅仅是使retaincount-1。不是调用dealloc函数
内存管理的原则：
假设使用alloc。copy创建的对象。一定要release
假设你retain一个对象，那么必需要release
Song 类的实现
#import <Foundation/Foundation.h>
@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全部元素，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;
}
属性简单介绍
@property 和@synthesize 能够自己主动生成某个类成员变量的存取方法，
语法 @property(參数) 类型 名字
这里的參数分为三大类：
读写属性：（readwrite/readonly） readwrite：这个属性是默认的，readonly：仅仅生成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
内存管理：（assign/retain/copy）assign：这个属性用来处理基础类型，比方int，float。假设你声明的类型就是基础类型，该属性能够不加
对于assign而言。set函数和get函数例如以下所看到的：
@property(nonatomic,assign)int val;
-(int)val
{
return val;
}
(void)setVal:(int)newVal
{
val=newVal;
}
copy：自己主动生成该对象的克隆
代码例如以下：
@property (nonatomic,copy) NSString *title;
{
return title;
}
-(void)settitle:(NSString*)newtitile
{
//首先推断是否与旧对象一致，假设不一致进行赋值。
if(newTitle!=title)
{
[title release];title=[newtitile copy];
}
}
retain：会自己主动retain对象。实现
代码例如以下：
@property (nonatomic,retain) NSString *title;
{
return title;
}
-(void)settitle:(NSString*)newtitile
{
//首先推断是否与旧对象一致。假设不一致进行赋值。