iOS——归档对象的创建，数据写入与读取

归档（archiving）是指另一种形式的序列化，但它是任何对象都可以实现的更常规的模型。专门编写用于保存数据的任何模型对象都应该支持归档。比属性列表多了很良好的伸缩性，因为无论添加多少对象，将这些对象写入磁盘的方式都相同。但使用属性列表，工作量会随着添加对象而增加。

创建一个工程，为ViewController。

新建两个类为NJperson

NJperson.h

#import <Foundation/Foundation.h>

// 如果想将一个自定义对象保存到文件中必须实现NSCoding协议
@interface NJPerson : NSObject <NSCoding>

@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) int age;
@property (nonatomic, assign) double height;
@end

NJperson.m

#import "NJPerson.h"

@implementation NJPerson

// 当将一个自定义对象保存到文件的时候就会调用该方法
// 在该方法中说明如何存储自定义对象的属性
// 也就说在该方法中说清楚存储自定义对象的哪些属性
- (void)encodeWithCoder:(NSCoder *)encoder
{
    NSLog(@"NJPerson encodeWithCoder");
    [encoder encodeObject:self.name forKey:@"name"];
    [encoder encodeInteger:self.age forKey:@"age"];
    [encoder encodeFloat:self.height forKey:@"heigth"];
}

// 当从文件中读取一个对象的时候就会调用该方法
// 在该方法中说明如何读取保存在文件中的对象
// 也就是说在该方法中说清楚怎么读取文件中的对象
- (id)initWithCoder:(NSCoder *)decoder
{
    NSLog(@"NJPerson initWithCoder");
    if (self = [super init]) {
        self.name = [decoder decodeObjectForKey:@"name"];
        self.age = [decoder decodeIntegerForKey:@"age"];
        self.height = [decoder decodeFloatForKey:@"heigth"];
    }
    return self;
}

_______在项目中创建两个按钮：一个为save,一个为read。

- (void)saveBtnClick:(id)sender{

NJStudent *stu = [[NJStudent alloc] init];
    stu.name = @"lnj";
    stu.age = 28;
    stu.height = 1.8;

// 2.获取文件路径
    NSString *docPath =  [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSString *path = [docPath stringByAppendingPathComponent:@"stu.xxoo"];
    NSLog(@"path = %@", path);
    
    // 3.将自定义对象保存到文件中

[NSKeyedArchiver archiveRootObject:stu toFile:path];

}

- (void)readBtnClick:(id)sender {

// 1.获取文件路径
    NSString *docPath =  [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSString *path = [docPath stringByAppendingPathComponent:@"stu.xxoo"];

// 2.从文件中读取对象
//    NJPerson *p = [NSKeyedUnarchiver unarchiveObjectWithFile:path];
    
    NJStudent *stu = [NSKeyedUnarchiver unarchiveObjectWithFile:path];

}

 对数据对象进行归档和取消归档的另外一个例子如下：

BIDFourLines.h

#import <Foundation/Foundation.h>

@interface BIDFourLines : NSObject<NSCoding,NSCopying>

@property(copy,nonatomic)NSArray *lines;

@end

BIDFourLines.m

#import "BIDFourLines.h"

static NSString *const kLinesKey = @"kLinesKey";

@implementation BIDFourLines

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

self = [super init];
    if (self) {
        
        self.lines = [aDecoder decodeObjectForKey:kLinesKey];
    }
    return self;
}

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

[aCoder encodeObject:self.lines forKey:kLinesKey];
}

#pragma mark copying
-(id)copyWithZone:(NSZone *)zone{

BIDFourLines *copy = [[[self class]allocWithZone:zone]init];
    NSMutableArray *linesCopy = [NSMutableArray array];
    
    for (id line in self.lines) {
        [linesCopy addObject:[line copyWithZone:zone]];
    }
    
    copy.lines = linesCopy;
    return copy;
}
@end

#import "ViewController.h"
#import "BIDFourLines.h"

static NSString *const kRootKey = @"kRootKey";

@interface ViewController ()

@property(strong,nonatomic)IBOutletCollection(UITextField)NSArray *lineFields;

@end

@implementation ViewController

-(NSString *)dataFilePath{
    
    //查找Document目录并在其后附加数据文件的文件名，这样就得到了数据文件的完整的路径

NSArray *paths = NSSearchPathForDirectoriesInDomains(
                    NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentDirectory = [paths objectAtIndex:0];
    
    return [documentDirectory stringByAppendingPathComponent:@"data.archive"];
}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    //
    NSString *filePath = [self dataFilePath];
    
    //检查数据文件在不在
    
    if ([[NSFileManager defaultManager]fileExistsAtPath:filePath]) {
        
        NSData *data = [[NSMutableData alloc]initWithContentsOfFile:filePath];
        
        NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc]initForReadingWithData:data];
        
        BIDFourLines *fourLines = [unarchiver decodeObjectForKey:kRootKey];
        [unarchiver finishDecoding];
        
        
        for (int i = 0; i < 4; i++) {
            
            UITextField *theField = self.lineFields[i];
            
            theField.text = fourLines.lines[i];
        }
    }
    
    UIApplication *app = [UIApplication sharedApplication];
    [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(applicationWillResignActive:) name:UIApplicationWillResignActiveNotification object:app];
    
}
//应用在终止运行或者进去后台之前保存数据

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

NSString *filePath = [self dataFilePath];
 
    BIDFourLines *fourLines = [[BIDFourLines alloc]init];
    fourLines.lines = [self.lineFields valueForKey:@"text"];
    
    NSMutableData *data = [[NSMutableData alloc]init];
    NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc]initForWritingWithMutableData:data];
    [archiver encodeObject:fourLines forKey:kRootKey];
    [archiver finishEncoding];
    
    [data writeToFile:filePath atomically:YES];

}
@end