IOS开发数据持久化篇文件存储(二)

前言:个人觉得开发人员最大的悲哀莫过于懂得使用却不明白其中的原理.在代码之前我觉得还是有必要简单阐述下相关的一些知识点. 因为文章或深或浅总有适合的人群.若有朋友发现了其中不正确的观点还望多多指出,不胜感激.

承接上篇博客我们来看看IOS开发中是如何将一个自定义的对象进行归档的
本篇博客将介绍以下几个方面的内容

1)普通的单个对象归档操作
2)拥有继承关系的对象归档
3)同时将多个对象进行归档

1.普通的单个对象归档操作

首先我们来看下最简单的单个对象归档操作
1.自定义一个跟小明一样有名的类(Person)

直接上代码 :

 Person.h

#import <Foundation/Foundation.h>

@interface Person : NSObject<NSCoding>

/**
 *  姓名
 */
@property (nonatomic, strong) NSString *name ;

/**
 *  地址
 */
@property (nonatomic, strong) NSString *address ;

/**
 *  年龄
 */
@property (nonatomic, assign) int age;


-(instancetype)initWithName:(NSString *)name address:(NSString *)address age:(int)age;//初始化方法

@end

Person.m

#import "Person.h"

@implementation Person

-(instancetype)initWithName:(NSString *)name address:(NSString *)address age:(int)age{
    if (self = [super init]) {
        self.name = name;
        self.address = address;
        self.age = age;
    }
    return self;
}

//告知编译器,我们需要归档当前对象的哪些属性
-(void)encodeWithCoder:(NSCoder *)aCoder{
    
    [aCoder encodeObject:self.name forKey:@"name"];
    [aCoder encodeObject:self.address forKey:@"address"];
    [aCoder encodeInt: self.age forKey:@"age"];
}

//告知编译器,解档时对应的属性
-(instancetype)initWithCoder:(NSCoder *)aDecoder{
    
    self.name = [aDecoder decodeObjectForKey:@"name"];
    self.address = [aDecoder decodeObjectForKey:@"address"];
    self.age = [aDecoder decodeIntForKey:@"age"];
    return self;
}

//重写description,方便调试查看对象属性信息
-(NSString *)description{
    return [NSString stringWithFormat:@"name : %@, address : %@,age : %d",self.name,self.address,self.age];
}

@end

控制器代码1:归档

-(void)personArchive{
    //创建及初始化对象
    Person *p = [[Person alloc] initWithName: @"jack" address:@"Mars" age:20];
    
    //定义归档路径
    NSString *fullPath = [self fullPathWithFileName:@"person.data"];
    
    //进行归档
    [NSKeyedArchiver archiveRootObject:p toFile:fullPath];
    
    NSLog(@"对象归档成功");
}

控制器代码2:解档

-(void)personUnarchive{
    //指定路径
    NSString *fullPath = [self fullPathWithFileName:@"person.data"];
    //解档操作
    Person *p = [NSKeyedUnarchiver unarchiveObjectWithFile:fullPath];
    //打印结果
    NSLog(@"%@",p);
    
}

注: fullPathWithFileName: 方法为便捷获取路径方法,代码如下

-(NSString *)fullPathWithFileName:(NSString *)fileName{

    NSString *documentDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)lastObject];
    //拼接完整路径并返回
    return [documentDir stringByAppendingPathComponent:fileName];

}

依次调用我们的归档和解档方法

 [self personArchive];//归档
 [self personUnarchive];//解档

结果如下:

至此我们已经实现了简单的单个对象的归档和解档操作,下面我们来看下继承关系下的对象的归档解档操作

2.拥有继承关系的对象归档和解档

定义一个Student类继承自Person类,代码如下

Student.h

#import "Person.h"

@interface Student : Person

/**
 *  学校名称
 */
@property (nonatomic, strong) NSString *schoolName;
//快速初始化方法
-(instancetype)initWithName:(NSString *)name address:(NSString *)address age:(int)age schoolName:(NSString *)schoolName;

@end

Student.m

#import "Student.h"

@implementation Student

-(instancetype)initWithName:(NSString *)name address:(NSString *)address age:(int)age schoolName:(NSString *)schoolName{
    if (self = [super initWithName:name address:address age:age]) {
        self.schoolName =schoolName;
    }
    return self;
}


-(void)encodeWithCoder:(NSCoder *)aCoder{
    
    [super encodeWithCoder:aCoder];
    
    [aCoder encodeObject:self.schoolName forKey:@"schoolName"];
}

-(instancetype)initWithCoder:(NSCoder *)aDecoder
{
    self = [super initWithCoder:aDecoder];
    self.schoolName = [aDecoder decodeObjectForKey:@"schoolName"];
    return self;
}

//重写description,方便调试查看属性信息
-(NSString *)description{
    
    //先拿到父类拥有的属性描述
    NSString *str = [super description];
    //添加子类特有的描述,返回
    return [str stringByAppendingString:[NSString  stringWithFormat:@",schoolName : %@",self.schoolName]];
}
@end

控制器方法1:归档

-(void)studentArchive{
    //声明一个子类对象
    Student *stu = [[Student alloc] initWithName:@"小明" address:@"走廊" age:10 schoolName:@"剑桥大学"];
    //定义路径
    NSString *fullpath = [self fullPathWithFileName:@"stu.data"];
    //归档操作
    [NSKeyedArchiver archiveRootObject:stu toFile:fullpath];
    
    NSLog(@"归档成功");
}

控制器方法2:解档

-(void)studentUnarchive{
    
    NSString *fullpath = [self fullPathWithFileName:@"stu.data"];//指定路径
    Student *stu = [NSKeyedUnarchiver unarchiveObjectWithFile:fullpath];//解档
    NSLog(@"%@",stu);//打印信息
}

依次调用上述两个方法,运行结果如下

3.同时将多个对象归档

演示代码如下:

1.归档

-(void)multipleArchive{
    //创建并初始化两个对象
    Student *s0 = [[Student alloc]initWithName:@"name0" address:@"address0" age:10 schoolName:@"schoolName0"];
    Student *s1 = [[Student alloc]initWithName:@"name1" address:@"address1" age:20 schoolName:@"schoolName1"];
   
    //创建一个NSMutableData对象
    NSMutableData *data = [NSMutableData data];
    NSKeyedArchiver *archive = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];//关联
    
    [archive encodeObject:s0 forKey:@"student0"];
    [archive encodeObject:s1 forKey:@"student1"];
    
    [archive finishEncoding];
    //指定路径
    NSString *fullpath = [self fullPathWithFileName:@"multiple.data"];
    //到这一步数据已缓存到data中,将其写入文件
    [data writeToFile:fullpath atomically:YES];
    
    NSLog(@"多对象归档成功");

}

02.解档:

-(void)multipleUnArchive{
    
    NSString *fullpath = [self fullPathWithFileName:@"multiple.data"];//指定路径
    NSData *data = [NSData dataWithContentsOfFile:fullpath];//将数据解析成NSData对象
    NSKeyedUnarchiver *unArchive = [[NSKeyedUnarchiver alloc]initForReadingWithData:data];//关联
    Student *stu0 = [unArchive decodeObjectForKey:@"student0"];
    Student *stu1 = [unArchive decodeObjectForKey:@"student1"];
    [unArchive finishDecoding];
    NSLog(@"%@",stu0);
    NSLog(@"%@",stu1);

}

运行结果如下图:

4.分析与简单总结

1.将一个对象归档的前提:

遵守NSCoding协议
实现两个方法:
encodeWithCoder://指定需要归档的属性
initWithCoder://指定需要解档的属性

2.继承关系的对象归档注意:

在实现上述两个方法的时候记得调用其父类的方法
eg:
[super encodeWithCoder:aCoder];
self = [super initWithCoder:aDecoder];

3.多对象归档依赖于:NSData对象