09. 属性的Attribute

内存管理

对象所有权政策 Object Onwership Policy

任何一个对象都有一定数量的所有者，当一个对象有至少一个所有者时，这个对象就会存在，如果一个对象没有所有者，也就是一个没有任何其他对象需要用这个对象，则这个对象就被系统销毁 ->调用dealloc方法

……

autorelease / NSAutoreleasePool

调用autorelease方法可在一段时间之后撤销所有权。

实质上，调用autorelease方法时，该对象会进入到一个自动释放池中。

什么时候撤销所有权？：当这个自动释放池接收到drain的消息时。

当一个自动释放池接收到drain消息时

1. 会调用池中所有对象的release方法。

2. 如果一个对象被两次加进同一个池中，则该对象此事会被池调用2次release.

3. 调用自动释放池的drain方法如同调用release方法，但一般都会写前者。

自动释放池可以被创建多个，如下：

NSAutoreleasePool pool = [[NSAutoreleasePool alloc] init];    //比较旧的方法

所有的自动释放池都会被放入到一个栈里。

属性访问器

property / synthesize / dot syntax

@property (属性的属性/Attribute of property) 实例变量类型 实例变量;

////  TRComputer.h//  day04-1////#import <Foundation/Foundation.h>#import "TRCpu.h"#import "TRMem.h"@interface TRComputer : NSObject@property(nonatomic, retain) TRCpu* cpu;@property(nonatomic, retain) TRMem* mem;-(void)playGame;-(id)initWithCpu:(TRCpu*)cpu andMem:(TRMem*)mem;+(id)computerWithCpu:(TRCpu*)cpu andMem:(TRMem*)mem;@end////  TRComputer.m//  day04-1////#import "TRComputer.h"@implementation TRComputer-(id)initWithCpu:(TRCpu *)cpu andMem:(TRMem *)mem{    if (self = [super init]) {        self.cpu = cpu;        self.mem = mem;    }    return self;}+(id)computerWithCpu:(TRCpu *)cpu andMem:(TRMem *)mem{    return [[[TRComputer alloc]initWithCpu:cpu andMem:mem]autorelease];}-(void)playGame{    NSLog(@"playGame CPU: %dGHZ Mem: %dGB size", self.cpu.hz, self.mem.size);}-(void)dealloc{    NSLog(@"computer cpu:%dHZ mem:%dGB销毁了", self.cpu.hz, self.mem.size);    [self.cpu release];    [self.mem release];    [super dealloc];}@end////  TRCpu.h//  day04-1////#import <Foundation/Foundation.h>@interface TRCpu : NSObject@property(nonatomic, assign) int hz;-(id)initWithHz:(int)hz;+(id)cpuWithHz:(int)hz;@end////  TRCpu.m//  day04-1////  Created by tarena on 14-3-20.//  Copyright (c) 2014年 tarena. All rights reserved.//#import "TRCpu.h"@implementation TRCpu-(id)initWithHz:(int)hz{    if (self = [super init]) {        self.hz = hz;    }    return self;}+(id)cpuWithHz:(int)hz{    return [[[TRCpu alloc]initWithHz:hz]autorelease];}-(void)dealloc{    NSLog(@"cpu %d销毁了", self.hz);    [super dealloc];}@end////  TRMem.h//  day04-1////  Created by tarena on 14-3-20.//  Copyright (c) 2014年 tarena. All rights reserved.//#import <Foundation/Foundation.h>@interface TRMem : NSObject@property(nonatomic, assign)int size;-(id)initWithSize:(int)size;+(id)memWithSize:(int)size;@end////  TRMem.m//  day04-1////  Created by tarena on 14-3-20.//  Copyright (c) 2014年 tarena. All rights reserved.//#import "TRMem.h"@implementation TRMem-(id)initWithSize:(int)size{    if (self = [super init]) {        self.size = size;    }    return self;}+(id)memWithSize:(int)size{    return [[[TRMem alloc]initWithSize:size]autorelease];}-(void)dealloc{    NSLog(@"mem %d销毁了", self.size);    [super dealloc];}@end////  main.m//  day04-1////  Created by tarena on 14-3-20.//  Copyright (c) 2014年 tarena. All rights reserved.//#import <Foundation/Foundation.h>#import "TRComputer.h"int main(int argc, const char * argv[]){    @autoreleasepool {                TRCpu* cpu1 = [TRCpu cpuWithHz:1];        TRMem* mem1 = [TRMem memWithSize:2];        TRComputer* computer = [TRComputer computerWithCpu:cpu1 andMem:mem1];        computer.cpu = cpu1;        computer.mem = mem1;        [computer playGame];                TRCpu* cpu2 = [TRCpu cpuWithHz:2];        TRMem* mem2 = [TRMem memWithSize:8];        computer.cpu = cpu2;        computer.mem = mem2;        [computer playGame];            }    return 0;}