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:];

     //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: 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: schoolName:@"schoolName0"];
     Student *s1 = [[Student alloc]initWithName:@"name1" address:@"address1" age: 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