数据存储-归档解档

1.介绍

一种可以把任意对象直接保存到文件的方式。
归档：把对象保存到文件中。
解档：从文件中读取对象。

2.注意：

归档会先清空文件，然后重新写入。

3.归档对象的写法

1.对象要实现 NSCoding 协议

@interface Student : NSObject

@property(nonatomic,copy)NSString *name;

@property(nonatomic,assign) CGFloat score;

@property(nonatomic,assign) BOOL sex;

@end

//1.基类写法
/**
 *  告诉系统需要归档的属性
 *
 *  @param aCoder 解析器
 */
- (void)encodeWithCoder:(NSCoder *)aCoder{
    [aCoder encodeObject:self.name forKey:@"name"];
    [aCoder encodeFloat:self.score forKey:@"score"];
    [aCoder encodeBool:self.sex forKey:@"sex"];
}

/**
 *  告诉系统解档出来的数据都需要怎么赋值
 *
 *  @param aDecoder 解析器
 *
 *  @return 对象
 */
- (instancetype)initWithCoder:(NSCoder *)aDecoder{
    if (self = [super init]) {
        self.name = [aDecoder decodeObjectForKey:@"name"];
        self.score = [aDecoder decodeFloatForKey:@"score"];
        self.sex = [aDecoder decodeBoolForKey:@"sex"];
    }
    return self;
}


//1.子类写法
- (void)encodeWithCoder:(NSCoder *)aCoder{
    //一定要调用一下父类的方法
    [super encodeWithCoder: aCoder];
    [aCoder encodeObject:self.name forKey:@"name"];
    [aCoder encodeFloat:self.score forKey:@"score"];
    [aCoder encodeBool:self.sex forKey:@"sex"];
}

- (instancetype)initWithCoder:(NSCoder *)aDecoder{
    //一定要调用一下父类的方法
    if (self = [super initWithCoder: aDecoder]) {
        self.name = [aDecoder decodeObjectForKey:@"name"];
        self.score = [aDecoder decodeFloatForKey:@"score"];
        self.sex = [aDecoder decodeBoolForKey:@"sex"];
    }
    return self;
}

4.归档 -- NSKeyedArchiver

//归档一个对象
- (void)save{
    //1.准备对象
    Student *stu = [[Student alloc] init];
    stu.name = @"zhangsan";
    stu.score = 90;
    stu.sex = YES;
    //2.要存储的文件路径
    NSString *filePath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    filePath = [filePath stringByAppendingPathComponent:@"student.data"];
    //3.归档
    [NSKeyedArchiver archiveRootObject:stu toFile:filePath];
}

//归档一组对象
- (void)save{
    //1.准备对象
    Student *stu = [[Student alloc] initWithName:@"zhangsan" withScore:90 withSex:YES];
    
    Student *stu1 = [[Student alloc] initWithName:@"lisi" withScore:90 withSex:YES];
    
    NSArray *arr = @[stu,stu1];
    //2.要存储的文件路径
    NSString *filePath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    filePath = [filePath stringByAppendingPathComponent:@"student.data"];
    //3.归档
    [NSKeyedArchiver archiveRootObject:arr toFile:filePath];
}

5.解档 -- NSKeyedUnarchiver

//解析单一对象
- (void)getData{
    //1.要存储的文件路径
    NSString *filePath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    filePath = [filePath stringByAppendingPathComponent:@"student.data"];
    //2.解档
    Student *stu = [NSKeyedUnarchiver unarchiveObjectWithFile:filePath];
}

//解档一组对象
- (void)getData{
    //2.要存储的文件路径
    NSString *filePath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    filePath = [filePath stringByAppendingPathComponent:@"student.data"];
    //3.解档
    NSArray *stus = [NSKeyedUnarchiver unarchiveObjectWithFile:filePath];
    NSLog(@"%@",stus);
}