系统相关
首页 > 系统相关> > objective C 内存管理及属性方法具体解释

objective C 内存管理及属性方法具体解释

作者:互联网

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;

-(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;

-(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。

 

标签:count,title,release,NSString,内存,objective,retain,Song1,属性
来源: https://www.cnblogs.com/mqxnongmin/p/10631278.html