ios數據存儲之--對模型對象歸檔(NSKeyedArchiver、NSKeyedUnarchiver)

轉載自：http://blog.csdn.net/mad1989/article/details/9106475

今天記錄一下學習 NSKeyedArchiver、NSKeyedUnarchiver ，主要用在ios數據存儲上，數據從內存存儲到閃存上，這個過程稱爲歸檔。

一、創建一個數據模型（自定義類）

現在就以大家常見的Student的爲例，這個模型有5個參數：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

通過以上的代碼我們可以看出，要實現對數據模型的歸檔，需要我們實現NScoding協議，NScoping（copy協議是爲了模型數據可以複製，對於歸檔而言，不是必須要實現）

NScoding協議需要實現兩個方法：

-(void)encodeWithCoder:(NSCoder *)aCoder    以keyValue形式對基本數據類型Encoding

-(id)initWithCoder:(NSCoder *)aDecoder     以keyValue形式對基本數據類型Decoding，返回數據模型本身

-(id)copyWithZone:(NSZone *)zone      NScopying協議的方法，目的爲了實現數據模型的copy，如下實例：

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

Log控制檯輸出：

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添加幾個針對數據模型的可編輯組件：

三、接下來就是在Viewcontroller.m中的操作，首先添加一個內部使用的方法，返回要保存到閃存的位置：

-(NSString *) getFilePath{

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

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

}

在ViewDidLoad方法裏，每次viewController初始化時，讀取路徑下的歸檔文件，讀取數據模型數據。同時添加一個通知每當按下Home鍵時，數據及時歸檔到閃存中。

- (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];

        //解檔出數據模型Student
        Student *mStudent = [unarchiver decodeObjectForKey:kDataKey];
        [unarchiver finishDecoding];//一定不要忘記finishDecoding，否則會報錯

        //接檔後就可以直接使用了（賦值到相應的組件屬性上）
        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];
    }

    //添加一個廣播，用於註冊當用戶按下home鍵時，歸檔數據到閃存中
    UIApplication *app = [UIApplication sharedApplication];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(saveAppDataWhenApplicationWillResignActive) name:UIApplicationWillResignActiveNotification object:app];

}

四、某一操作需要保存數據的時候，及時歸檔到閃存中

/**
 *當用戶按下Home鍵，返回桌面時，歸檔當前數據到指定文件路徑下
 */
-(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];


}

運行效果：

重新運行後：

歸檔這種保存方式缺點就是沒有屬性列表（NSuserDefault）速度快，因爲它每次都要把文件保存到閃存中，優點是可以創建自己想要的數據模型，然後統一以模型方式存儲，比屬性列表要過分依賴Key要省心。

目前就記錄這麼多，以後再有的話再補充，如果有什麼錯誤歡迎大家指出，一起學習，進步。