ios学习笔记——对象归档

对象归档是一种序列化方式。为了便于数据传输，先将归档对象序列化为一个文件，然后再通过反归档将数据恢复到对象中。

归档技术可以实现数据的持久化，不过在大量数据和频繁读写的情况下，它就不太适合了。

对一个对象进行归档的条件是：改对象的类必须实现NSCoding协议，而且每个成员对象应该是基本数据类型或都是实现NSCoding协议的某个类的实例。

一、使用NSKeyedArchiver进行简单归档

---

    NSString * path = NSHomeDirectory();
    NSString * filePath = [path stringByAppendingPathComponent:@"sjz.txt"];
    //归档，这里可以是NSString、NSDate、NSArray、NSDictionary等
    [NSKeyedArchiver archiveRootObject:@"sjz" toFile:filePath];
    
    //反归档
    NSString * str = [NSKeyedUnarchiver unarchiveObjectWithFile:filePath];

这种方式在写入、读出数据之前对数据惊醒序列化、反序列化操作，可以对基本类型数据进行归档。但是这样只能把一个对象归档进一个文件中。

二、多个数据的归档

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当有多个数据的时候，我们就需要NSData的帮助了。

NSData封装了字典数据的缓存类，提供了数据文件的方法:

+ (instancetype)dataWithContentsOfFile:(NSString *)path

+ (instancetype)dataWithContentsOfFile:(NSString *)path  options:(NSDataReadingOptions)mask error:(NSError * _Nullable *)errorPtr

- (instancetype)initWithContentsOfFile:(NSString *)path

- (instancetype)initWithContentsOfFile:(NSString *)path options:(NSDataReadingOptions)mask error:(NSError * _Nullable *)errorPtr

上面四个方法用于从文件中读取数据创建NSData对象

- (BOOL)writeToFile:(NSString *)path atomically:(BOOL)atomically

- (BOOL)writeToFile:(NSString *)path options:(NSDataWritingOptions)mask error:(NSError * _Nullable *)errorPtr

这两个方法用于将NSData里的数据写的文件中去

//文件路径
    NSString * path = NSHomeDirectory();
    NSString * filePath = [path stringByAppendingPathComponent:@"sjz.txt"];
    
    NSString * str = @"小明";
    NSString * age = @"10";
    NSArray * arr = [NSArray arrayWithObjects:@"123", @"456", @"789", nil];
    NSInteger integer = 10;
    
    //归档
    NSMutableData * data = [[NSMutableData alloc] init];
    NSKeyedArchiver * archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
    [archiver encodeObject:str forKey:@"name"];
    [archiver encodeObject:age forKey:@"age"];
    [archiver encodeObject:arr forKey:@"arr"];
    [archiver encodeInteger:integer forKey:@"integer"];
    [archiver finishEncoding];
    [data writeToFile:filePath atomically:YES];
    
    //反归档
    NSMutableData * unData = [[NSMutableData alloc] initWithContentsOfFile:filePath];
    NSKeyedUnarchiver * unArchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:unData];
    NSString * name = [unArchiver decodeObjectForKey:@"name"];
    NSString * ageStr = [unArchiver decodeObjectForKey:@"age"];
    NSArray  * array = [unArchiver decodeObjectForKey:@"arr"];
    NSInteger intt = [unArchiver decodeIntegerForKey:@"integer"];
    [unArchiver finishDecoding];
    
    NSLog(@"name = %@, age = %@", name, ageStr);
    NSLog(@"%@", array);
    NSLog(@"%ld", intt);

归档时，我们先将所需的数据归档到NSData中，再将NSData数据写到文件中。

反归档时，我们先从文件中读取数据到NSData中，再根据键值烦归档

第三、自定义对象的归档

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上边说的是基本对象的归档，但是我们自己定义的实例对象怎么归档呢？

但我们按Home键将程序后台运行时，很多情况下我们要将数据保存，当程序恢复时，数据重新加载，那么归档是一个好的选择。

我们自定义的类想要实现归档与反归档，必须实现NSCoding协议，并实现协议中的两个方法：- (void)encodeWithCoder:(NSCoder *)aCoder 和 - (instancetype)initWithCoder:(NSCoder *)aDecoder

自定义类：

#import <Foundation/Foundation.h>

@interface JZModel : NSObject <NSCoding>

@property (nonatomic, strong) NSString * name;
@property (nonatomic, assign) NSInteger age;
@property (nonatomic, strong) NSString * address;

@end

#import "JZModel.h"

@implementation JZModel

//必须实现，归档
- (void)encodeWithCoder:(NSCoder *)aCoder
{
    [aCoder encodeObject:_name forKey:@"name"];
    [aCoder encodeInteger:_age forKey:@"age"];
    [aCoder encodeObject:_address forKey:@"address"];
}

//必须实现，反归档
- (instancetype)initWithCoder:(NSCoder *)aDecoder
{
    self = [super init];
    if(self){
        _name = [aDecoder decodeObjectForKey:@"name"];
        _age = [aDecoder decodeIntegerForKey:@"age"];
        _address = [aDecoder decodeObjectForKey:@"address"];
    }
    
    return self;
}


- (NSString *)description
{
    return [NSString stringWithFormat:@"姓名：%@，年龄：%ld，地址：%@", self.name, self.age, self.address];
}

@end

实现归档与反归档的代码：

NSString * homePath = NSHomeDirectory();
    NSString * filePath = [homePath stringByAppendingPathComponent:@"sjz.plist"];
    
    JZModel * model = [[JZModel alloc] init];
    model.name = @"jz";
    model.age = 20;
    model.address = @"河北大街";
    
    //归档
    NSMutableData * data = [[NSMutableData alloc] init];
    NSKeyedArchiver * archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
    [archiver encodeObject:model forKey:@"model"];
    [archiver finishEncoding];
    [data writeToFile:filePath atomically:YES];
    
    
    //反归档
    NSMutableData * data1 = [[NSMutableData alloc] initWithContentsOfFile:filePath];
    NSKeyedUnarchiver * unArchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data1];
    JZModel * model1 = [unArchiver decodeObjectForKey:@"model"];
    [unArchiver finishDecoding];
    
    NSLog(@"%@", model1);

输出结果：