Objective-C日记-之编码对象属性

NSCoder类

1，概述

将对象的实例变量和其他数据编码为数据块，然后将他们存在到磁盘当中；以后将这些数据块读回到内存中，并且还基于保存的数据创建新的对象，也称序列化或反序列化。

2，用法

a,首先，定义一个类，使其遵守<NSCoding>协议

@interface Thingie:NSObject <NSCoding>{

NSString *name;

int magicNumber;

float shoeSize;

NSMutableArray *subThingies;

}

@property (copy) NSString *name;

@property int magicNumber;

@property float shoeSize;

@property (retain) NSMutableArray *subThingies;

-(id)initWithName:(NSString *)n

magicNumber:(int)mn

shoeSize:(float)ss;

@end//interface Thingie

实现类

@implementation Thingie

@synthesize name;

@synthesize magicNumber;

@synthesize shoeSize;

@synthesize subThingies;

-(id)initWithName:(NSString *)n

magicNumber:(int)mn

shoeSize:(float)ss{

if(self==[super init]){

self.name=n;

self.magicNumber=mn;

self.shoeSize=ss;

self.subThingies=[NSMutableArray array];

}

return self;

}

实现<NSCoding>协议中的-encoderWithCoder和-initWithCoder

接以上代码

-(void)encoderWithCoder:(NSCoder*)coder{

[coder encodeObject:name

forKey:@"name"];

[coder encodeObject:magicNumber

forKey:@"magicNumber"];

[coder encodeObject:shoeSize

forKey:@"shoeSize"];

[coder encodeObject:subThingies

forKey:@"subThingies"];

}//encodeWithCoder

-(id)initWithCoder:(NSCoder *)decoder{

if(self=[super init]{

self.name=[decoder decodeObjectForKey:@"name"];

self.magicNumber=[decoder decodeIntForKey:@"magicNumber"];

self.shoeSize=[decoder decodeFloatForKey:@"shoeSize"];

self.subThingies=[decoder decodeObjectForKey:@"subThingies"];

}

return self;

}//initWithCoder

b,再次，使用该类定义一个对象，初始化它。

Thingie *thing1;

thing1=[[Thingie alloc]

initWithName:@"thing1"

magicNumber:42

shoeSize:10.5];

c,定义一个NSData对象，并使用类方法：NSKeydArchiver对对象进行编码后赋值给NSData对象。

NSData *freezeDried;

freezeDried=[NSKeyedArchiver archivedDataWithRootObject:thing1];

d,如果愿意，可以将NSData对象存储到磁盘上

[freezeDried writeToFile:@"/tmp/verbiage.txt"

atomically:YES];

f,解码NSData

thing1=[NSKeyedUnarchiver unarchiverObjectWithData:freezeDried];

3,注意点

如上所示例中，NSMultableArray对象subThingies可以存放各种对象，但是不能存储NSlog类，因为它不能检测对象循环。