ios数据存储之--对模型对象归档(NSKeyedArchiver、NSKeyedUnarchiver)

今天记录一下学习 NSKeyedArchiver、NSKeyedUnarchiver ，主要用在ios数据存储上，数据从内存存储到闪存上，这个过程称为归档。

一、创建一个数据模型（自定义类）

现在就以大家常见的Student的为例，这个模型有5个参数：name、age、weight、hobby、others

Student.h

#import <Foundation/Foundation.h>

@interface Student : NSObject<NSCoding,NSCopying>

@property(copy,nonatomic) NSString *name;
@property(assign,nonatomic) int age;
@property(assign,nonatomic) double  weight;
@property(copy,nonatomic) NSArray *hobby;
@property(copy,nonatomic) NSDictionary *others;

@end

Student.m

#import "Student.h"

#define knameKey @"name"
#define kageKey @"age"
#define kweightKey @"weight"
#define khobbyKey @"hobby"
#define kotherKey @"others"

@implementation Student

@synthesize name;
@synthesize age;
@synthesize weight;
@synthesize hobby;
@synthesize others;

#pragma mark-NSCoding
-(void)encodeWithCoder:(NSCoder *)aCoder{

[aCoder encodeObject:name forKey:knameKey];
[aCoder encodeInt:age forKey:kageKey];
[aCoder encodeDouble:weight forKey:kweightKey];
[aCoder encodeObject:hobby forKey:khobbyKey];
[aCoder encodeObject:others forKey:kotherKey];

}

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

if (self == [super init]) {
name =  [aDecoder decodeObjectForKey:knameKey];
age = [aDecoder decodeIntForKey:kageKey];
weight =  [aDecoder decodeDoubleForKey:kweightKey];
hobby =  [aDecoder decodeObjectForKey:khobbyKey];
others =  [aDecoder decodeObjectForKey:kotherKey];
}

return self;
}

#pragma mark-NSCopying
-(id)copyWithZone:(NSZone *)zone{
Student *copy = [[[self class] allocWithZone:zone] init];
copy.name = [self.name copyWithZone:zone];
copy.age = self.age;
copy.weight = self.weight;
copy.hobby = [self.hobby copyWithZone:zone];
copy.others = [self.others copyWithZone:zone];

return copy;
}

@end

通过以上的代码我们可以看出，要实现对数据模型的归档，需要我们实现NScoding协议，NScoping（copy协议是为了模型数据可以复制，对于归档而言，不是必须要实现）

NScoding协议需要实现两个方法：

-(void)encodeWithCoder:(NSCoder *)aCoder
以keyValue形式对基本数据类型Encoding
-(id)initWithCoder:(NSCoder *)aDecoder
以keyValue形式对基本数据类型Decoding，返回数据模型本身

-(id)copyWithZone:(NSZone *)zone NScopying协议的方法，目的为了实现数据模型的copy，如下实例：

Student *s1 = [[Student alloc] init];
Student *s2 = [s1 copy];
NSLog(@"s1:%@",s1);
NSLog(@"s2:%@",s2);

Log控制台输出：
2013-06-16 16:19:36.157 ArchiveDemo[1357:c07] s1:<Student: 0x8875340>
2013-06-16 16:19:36.158 ArchiveDemo[1357:c07] s2:<Student: 0x8875360>

二、ViewController.xib添加几个针对数据模型的可编辑组件：





三、接下来就是在Viewcontroller.m中的操作，首先添加一个内部使用的方法，返回要保存到闪存的位置：

-(NSString *) getFilePath{

NSArray *array =  NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

return [[array objectAtIndex:0] stringByAppendingPathComponent:kFileName];

}

在ViewDidLoad方法里，每次viewController初始化时，读取路径下的归档文件，读取数据模型数据。同时添加一个通知每当按下Home键时，数据及时归档到闪存中。

- (void)viewDidLoad
{
[super viewDidLoad];

if ([[NSFileManager defaultManager] fileExistsAtPath:[self getFilePath]]) {
NSLog(@"filePAth:%@",[self getFilePath]);

NSData *data = [[NSData alloc] initWithContentsOfFile:[self getFilePath]];

NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];

//解档出数据模型Student
Student *mStudent = [unarchiver decodeObjectForKey:kDataKey];
[unarchiver finishDecoding];//一定不要忘记finishDecoding，否则会报错

//接档后就可以直接使用了（赋值到相应的组件属性上）
self.nameLabel.text = mStudent.name;
self.ageLabel.text = [NSString stringWithFormat:@"%d",mStudent.age];
self.weightLabel.text = [NSString stringWithFormat:@"%f",mStudent.weight];
self.hobbyTextField.text = [mStudent.hobby objectAtIndex:0];
self.othersTextView.text = [mStudent.others objectForKey:@"other"];

[unarchiver release];
[data release];
}

//添加一个广播，用于注册当用户按下home键时，归档数据到闪存中
UIApplication *app = [UIApplication sharedApplication];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(saveAppDataWhenApplicationWillResignActive) name:UIApplicationWillResignActiveNotification object:app];

}

四、某一操作需要保存数据的时候，及时归档到闪存中

/**
*当用户按下Home键，返回桌面时，归档当前数据到指定文件路径下
*/
-(void) saveAppDataWhenApplicationWillResignActive:(NSNotification*) notification{

Student *saveStudent = [[Student alloc] init];
saveStudent.name = self.nameLabel.text;
saveStudent.age = [self.ageLabel.text intValue];
saveStudent.weight = [self.weightLabel.text doubleValue];
saveStudent.hobby = [NSArray arrayWithObjects:self.hobbyTextField.text, nil];
saveStudent.others = [NSDictionary dictionaryWithObjectsAndKeys:self.othersTextView.text,@"other",nil];

NSMutableData *data = [[NSMutableData alloc] init];

NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];

[archiver encodeObject:saveStudent forKey:kDataKey];

[archiver finishEncoding];

[data writeToFile:[self getFilePath] atomically:YES];
[data release];
[archiver release];
[saveStudent release];

}

运行效果：


重新运行后：


归档这种保存方式缺点就是没有属性列表（NSuserDefault）速度快，因为它每次都要把文件保存到闪存中，优点是可以创建自己想要的数据模型，然后统一以模型方式存储，比属性列表要过分依赖Key要省心。

目前就记录这么多，以后再有的话再补充，如果有什么错误欢迎大家指出，一起学习，进步。