IPhone 之模型对象归档

    归档指的是另一种型式的序列化，但它是任保对象都可以实现的更常规的类型。

    其作用为：进行数据的持久化保存。

    对象必须实现 NSCodeing 协议和 NSCopying 协议。
  

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@interface FourLines : NSObject <NSCoding, NSCopying> {

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    NSString *field1;

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    NSString *field2;

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    NSString *field3;

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    NSString *field4;   

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}

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@property (nonatomic, retain) NSString *field1;

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@property (nonatomic, retain) NSString *field2;

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@property (nonatomic, retain) NSString *field3;

10 @property (nonatomic, retain) NSString *field4;
11 @end
12 #pragma mark NSCoding
13 - (void)encodeWithCoder:(NSCoder *)encoder {
14     [encoder encodeObject:field1 forKey:kField1Key];
15     [encoder encodeObject:field2 forKey:kField2Key];
16     [encoder encodeObject:field3 forKey:kField3Key];
17     [encoder encodeObject:field4 forKey:kField4Key];
18 }
19 - (id)initWithCoder:(NSCoder *)decoder {
20     if (self = [super init]) {
21         self.field1 = [decoder decodeObjectForKey:kField1Key];
22         self.field2 = [decoder decodeObjectForKey:kField2Key];
23         self.field3 = [decoder decodeObjectForKey:kField3Key];
24         self.field4 = [decoder decodeObjectForKey:kField4Key];
25     }
26     return self;
27 }
28 #pragma mark NSCopying
29 - (id)copyWithZone:(NSZone *)zone {
30     FourLines *copy = [[[self class] allocWithZone: zone] init];
31     copy.field1 = [[self.field1 copyWithZone:zone] autorelease];
32     copy.field2 = [[self.field2 copyWithZone:zone] autorelease];