iOS 数据持久性存储-对象归档

对象归档是将对象归档以文件的形式保存到磁盘中(也称为序列化，持久化)，使用的时候读取该文件的保存路径读取文件的内容（也称为解档，反序列化）

主要涉及两个类：NSKeyedArichiver、NSKeyedUnarchiver

两个协议NSCoding的2个方法:

　　- (void)encodeWithCoder:

　　- (id)initWithCoder:

可以接着(一)的例子，新建文件，subclass of NSObject, 实现NSCoding协议

新建文件.h

#import <Foundation/Foundation.h>

@interface BSLFourLines : NSObject<NSCoding>

@property (copy, nonatomic) NSString *field1;

@property (copy, nonatomic) NSString *field2;

@property (copy, nonatomic) NSString *field3;

@property (copy, nonatomic) NSString *field4;

@end

新建文件.m

#import "BSLFourLines.h"

#define kField1Key @"Field1"

#define kField2Key @"Field2"

#define kField3Key @"Field3"

#define kField4Key @"Field4"

@implementation BSLFourLines

@synthesize field1,field2,field3,field4;

#pragma mark NSCoding

//以keyValue形式对基本数据类型Encoding

- (void)encodeWithCoder:(NSCoder *)aCoder{

    [aCoder encodeObject:field1 forKey:kField1Key];

    [aCoder encodeObject:field2 forKey:kField2Key];

    [aCoder encodeObject:field3 forKey:kField3Key];

    [aCoder encodeObject:field4 forKey:kField4Key];

}

//以keyValue形式对基本数据类型Decoding，返回数据模型本身

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

    if (self = [super init]) {

        field1 = [aDecoder decodeObjectForKey:kField1Key];

        field2 = [aDecoder decodeObjectForKey:kField2Key];

        field3 = [aDecoder decodeObjectForKey:kField3Key];

        field4 = [aDecoder decodeObjectForKey:kField4Key];

    }

    return self;

}

现在转到XXViewController.m在#import下方添加

#import "BSLFourLines.h"

#define kFilename2 @"archive"

#define kDataKey @"Data"

改动后的方法内容

- (void)viewDidLoad

{

    [super viewDidLoad];

    NSString *filePath = [self dataFilePath];

    //检查数据文件是否存在，如果存在就用此文件内容实例化数组

    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {

        NSData *data = [[NSMutableData alloc] initWithContentsOfFile:[self dataFilePath]];

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

        BSLFourLines *fourLines = [unarchiver decodeObjectForKey:kDataKey];

        [unarchiver finishDecoding];

        field1.text = fourLines.field1;

        field2.text = fourLines.field2;

        field3.text = fourLines.field3;

        field4.text = fourLines.field4;

    }

//通知

    UIApplication *app = [UIApplication sharedApplication];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationWillResignActive:) name:UIApplicationWillResignActiveNotification object:app];

}

- (void)applicationWillResignActive:(NSNotification *)notification{

    BSLFourLines *fourLines = [[BSLFourLines alloc] init];

    fourLines.field1 = field1.text;

    fourLines.field2 = field2.text;

    fourLines.field3 = field3.text;

    fourLines.field4 = field4.text;

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

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

    [archiver encodeObject:fourLines forKey:kDataKey];

    [archiver finishEncoding];

    [data writeToFile:[self dataFilePath] atomically:YES];

}

如果需要对自定义的类进行copy的话，需要在自定义类实现<NSCoding>协议

自定义类的实现文件里添加下列方法

- (id)copyWithZone:(NSZone *)zone{

    BSLFourLines *copy = [[[self class] allocWithZone:zone] init];

    copy.field1 = [self.field1 copyWithZone:zone];

    copy.field2 = [self.field2 copyWithZone:zone];

    copy.field3 = [self.field3 copyWithZone:zone];

    copy.field4 = [self.field4 copyWithZone:zone];

    return copy;

}