ios数据存储——对象归档

归档：数据从内存与闪存相互转化，类似“序列化”，将数据转换成二进制字节数据

操作：有两种方式，第一种是单个对象作为root进行归档和恢复，一个对象一个文件；第二种，可以同时归档多个对象到一个文件

注意：归档自定义对象，需要实现NSCoding协议里的两个方法，举例说明：【preference】http://blog.csdn.net/mad1989/article/details/9106475

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。