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;
}