数据持久化基础知识——归档

使用对象模型进行归档，将对象写入文件，再从中读取它们。

1.首先的创建一个类，FourLines类.

FourLines.h

#import <Foundation/Foundation.h>

//数据模型，存储当前存储在属性列表应用的字典中的数据。
@interface FourLines : NSObject <NSCopying, NSCoding>
@property (copy, nonatomic) NSArray * lines;
@end

FourLines.m

#import "FourLines.h"

static NSString * const kLinesKey = @"kLinesKey";

@implementation FourLines

#pragma mark - Coding
//对4个属性进行解码
- (id)initWithCoder:(NSCoder *)aDecoder
{
    self = [super init];
    if (self) {
        self.lines = [aDecoder decodeObjectForKey:kLinesKey];
    }
    return self;
}
//对4个属性进行编码
- (void)encodeWithCoder:(NSCoder *)aCoder
{
    [aCoder encodeObject:self.lines forKey:kLinesKey];
}

#pragma mark - Coping
//新建一个对象，将4个字符串复制到对象中。
- (id)copyWithZone:(NSZone *)zone
{
    FourLines * 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

ViewController.m

#import "ViewController.h"
#import "FourLines.h"

static NSString * const kRootKey = @"kRootKey";

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

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    NSString * filePath = [self dataFilePath];
    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
        
//        NSArray * array = [[NSArray alloc] initWithContentsOfFile:filePath];
//        for (int i = 0; i < 4; i++) {
//            UITextField * theField = self.lineFields[i];
//            theField.text = array[i];
//        }
        
        NSData * data = [[NSMutableData alloc] initWithContentsOfFile:filePath];
        NSKeyedUnarchiver * unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
        FourLines * 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];
}
- (NSString *)dataFilePath
{
    NSArray * paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString * documentsDirectory = [paths objectAtIndex:0];
//    return [documentsDirectory stringByAppendingPathComponent:@"data.plist"];
    return [documentsDirectory stringByAppendingPathComponent:@"data.archive"];
}
- (void)applicationWillResignActive:(NSNotification *)notification
{
    NSString * filePath = [self dataFilePath];
//    NSArray * array = [self.lineFields valueForKey:@"text"];
//    [array writeToFile:filePath atomically:YES];
    
    FourLines * fourLines = [[FourLines 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];
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end