IOS开发--数据持久化篇之文件存储(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

1 #import <Foundation/Foundation.h>
2
3 @interface Person : NSObject<NSCoding>
4
5 /**
6  *  姓名
7  */
8 @property (nonatomic, strong) NSString *name ;
9
10 /**
11  *  地址
12  */
13 @property (nonatomic, strong) NSString *address ;
14
15 /**
16  *  年龄
17  */
18 @property (nonatomic, assign) int age;
19
20
21 -(instancetype)initWithName:(NSString *)name address:(NSString *)address age:(int)age;//初始化方法
22
23 @end

 

Person.m

1 #import "Person.h"
2
3 @implementation Person
4
5 -(instancetype)initWithName:(NSString *)name address:(NSString *)address age:(int)age{
6     if (self = [super init]) {
7         self.name = name;
8         self.address = address;
9         self.age = age;
10     }
11     return self;
12 }
13
14 //告知编译器,我们需要归档当前对象的哪些属性
15 -(void)encodeWithCoder:(NSCoder *)aCoder{
16
17     [aCoder encodeObject:self.name forKey:@"name"];
18     [aCoder encodeObject:self.address forKey:@"address"];
19     [aCoder encodeInt: self.age forKey:@"age"];
20 }
21
22 //告知编译器,解档时对应的属性
23 -(instancetype)initWithCoder:(NSCoder *)aDecoder{
24
25     self.name = [aDecoder decodeObjectForKey:@"name"];
26     self.address = [aDecoder decodeObjectForKey:@"address"];
27     self.age = [aDecoder decodeIntForKey:@"age"];
28     return self;
29 }
30
31 //重写description,方便调试查看对象属性信息
32 -(NSString *)description{
33     return [NSString stringWithFormat:@"name : %@, address : %@,age : %d",self.name,self.address,self.age];
34 }
35
36 @end

 

控制器代码1:归档

1 -(void)personArchive{
2     //创建及初始化对象
3     Person *p = [[Person alloc] initWithName: @"jack" address:@"Mars" age:20];
4
5     //定义归档路径
6     NSString *fullPath = [self fullPathWithFileName:@"person.data"];
7
8     //进行归档
9     [NSKeyedArchiver archiveRootObject:p toFile:fullPath];
10
11     NSLog(@"对象归档成功");
12 }

 

控制器代码2:解档

1 -(void)personUnarchive{
2     //指定路径
3     NSString *fullPath = [self fullPathWithFileName:@"person.data"];
4     //解档操作
5     Person *p = [NSKeyedUnarchiver unarchiveObjectWithFile:fullPath];
6     //打印结果
7     NSLog(@"%@",p);
8
9 }

 

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

1 -(NSString *)fullPathWithFileName:(NSString *)fileName{
2
3     NSString *documentDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)lastObject];
4     //拼接完整路径并返回
5     return [documentDir stringByAppendingPathComponent:fileName];
6
7 }

 

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

1 #import "Person.h"
2
3 @interface Student : Person
4
5 /**
6  *  学校名称
7  */
8 @property (nonatomic, strong) NSString *schoolName;
9 //快速初始化方法
10 -(instancetype)initWithName:(NSString *)name address:(NSString *)address age:(int)age schoolName:(NSString *)schoolName;
11
12 @end

 

Student.m

1 #import "Student.h"
2
3 @implementation Student
4
5 -(instancetype)initWithName:(NSString *)name address:(NSString *)address age:(int)age schoolName:(NSString *)schoolName{
6     if (self = [super initWithName:name address:address age:age]) {
7         self.schoolName =schoolName;
8     }
9     return self;
10 }
11
12
13 -(void)encodeWithCoder:(NSCoder *)aCoder{
14
15     [super encodeWithCoder:aCoder];
16
17     [aCoder encodeObject:self.schoolName forKey:@"schoolName"];
18 }
19
20 -(instancetype)initWithCoder:(NSCoder *)aDecoder
21 {
22     self = [super initWithCoder:aDecoder];
23     self.schoolName = [aDecoder decodeObjectForKey:@"schoolName"];
24     return self;
25 }
26
27 //重写description,方便调试查看属性信息
28 -(NSString *)description{
29
30     //先拿到父类拥有的属性描述
31     NSString *str = [super description];
32     //添加子类特有的描述,返回
33     return [str stringByAppendingString:[NSString  stringWithFormat:@",schoolName : %@",self.schoolName]];
34 }
35 @end

 

控制器方法1:归档

1 -(void)studentArchive{
2     //声明一个子类对象
3     Student *stu = [[Student alloc] initWithName:@"小明" address:@"走廊" age:10 schoolName:@"剑桥大学"];
4     //定义路径
5     NSString *fullpath = [self fullPathWithFileName:@"stu.data"];
6     //归档操作
7     [NSKeyedArchiver archiveRootObject:stu toFile:fullpath];
8
9     NSLog(@"归档成功");
10 }

 

控制器方法2:解档

1 -(void)studentUnarchive{
2
3     NSString *fullpath = [self fullPathWithFileName:@"stu.data"];//指定路径
4     Student *stu = [NSKeyedUnarchiver unarchiveObjectWithFile:fullpath];//解档
5     NSLog(@"%@",stu);//打印信息
6 }

 

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

1 -(void)multipleArchive{
2     //创建并初始化两个对象
3     Student *s0 = [[Student alloc]initWithName:@"name0" address:@"address0" age:10 schoolName:@"schoolName0"];
4     Student *s1 = [[Student alloc]initWithName:@"name1" address:@"address1" age:20 schoolName:@"schoolName1"];
5
6     //创建一个NSMutableData对象
7     NSMutableData *data = [NSMutableData data];
8     NSKeyedArchiver *archive = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];//关联
9
10     [archive encodeObject:s0 forKey:@"student0"];
11     [archive encodeObject:s1 forKey:@"student1"];
12
13     [archive finishEncoding];
14     //指定路径
15     NSString *fullpath = [self fullPathWithFileName:@"multiple.data"];
16     //到这一步数据已缓存到data中,将其写入文件
17     [data writeToFile:fullpath atomically:YES];
18
19     NSLog(@"多对象归档成功");
20
21 }

 

02.解档:

1 -(void)multipleUnArchive{
2
3     NSString *fullpath = [self fullPathWithFileName:@"multiple.data"];//指定路径
4     NSData *data = [NSData dataWithContentsOfFile:fullpath];//将数据解析成NSData对象
5     NSKeyedUnarchiver *unArchive = [[NSKeyedUnarchiver alloc]initForReadingWithData:data];//关联
6     Student *stu0 = [unArchive decodeObjectForKey:@"student0"];
7     Student *stu1 = [unArchive decodeObjectForKey:@"student1"];
8     [unArchive finishDecoding];
9     NSLog(@"%@",stu0);
10     NSLog(@"%@",stu1);
11
12 }

 

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