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。