IOS之NSCoing协议实现

近期学习NSCoding协议，发现很多小的问题，特把自己学习写的代码放到这里，供一起学习的参考一下，很简单，大神请绕过。

1. 首先定义了一Person类，对其实现NSCoding协议

 **** .h文件 ****
 #import 

 @interface Person : NSObject
 @property(nonatomic,strong) NSString * name;
 @property(nonatomic,strong) NSString * gender;
 @property(nonatomic,strong) NSString * address;
 @property(nonatomic) NSUInteger age;
 -(instancetype)initWithName:(NSString*)name gender:(NSString*)gender address:(NSString*)adderss age:(NSUInteger)age;
 +(instancetype)  FactoryWithName:(NSString*)name gender:(NSString*)gender address:(NSString*)adderss age:(NSUInteger)age;
 -(void)function;

**** .m文件 ****
#import "Person.h"
@implementation Person
-(instancetype)initWithName:(NSString *)name gender:(NSString *)gender address:(NSString *)adderss age:(NSUInteger)age{
    if (self = [super init]) {
        _name = name;
        _gender = gender;
        _address = adderss;
        _age = age;
    }
    return self;

}
+(instancetype)FactoryWithName:(NSString *)name gender:(NSString *)gender address:(NSString *)adderss age:(NSUInteger)age{
    return [[self alloc]initWithName:name gender:gender address:adderss age:age];
}
 -(void)function{
    NSLog(@"我是一个人");

}
 //为了打印对象信息方便，从写了description方法
-(NSString*)description{
    return [NSString stringWithFormat:@"name:%@  gender:%@  age:%lu address:%@",self.name,self.gender,(unsigned long)self.age,self.address];

}
//这里对NSCoding协议进行实现，由于返回一个对象，就需要创建一个对象并返回，
//这里使用［self class］获取类，而不是直接使用Person类进行创建，是为了它的
//子类实现协议时候，调用父类的方法，返回的是子类的对象而不是父类的对象。如果
//子类没有增加实例变量还好，如多增加，由于返回的是父类对象，由于不存在子类
//添加的属性，调用不存在或者为不存在的属性赋值会出错。下面子类再次说明本问题。
  
-(instancetype)copyWithZone:(NSZone *)zone{
        return [[[self class] allocWithZone:zone] initWithName:［_name copy］ gender:［_gender copy］ address:［_address copy］ age:_age];

}
@end

2.继承自Person类创建Student类

**** .h文件  ****
#import "Person.h"
@interface Student : Person
@property(nonatomic) NSUInteger score;
-(instancetype)initWithName:(NSString *)name gender:(NSString *)gender address:(NSString *)adderss age:(NSUInteger)age score:(NSUInteger)score;
+(instancetype)factoryWithName:(NSString *)name gender:(NSString *)gender address:(NSString *)adderss age:(NSUInteger)age score:(NSUInteger)score;

@end

**** .m文件 ****
#import "Student.h"

@implementation Student
-(instancetype)initWithName:(NSString *)name gender:(NSString *)gender address:(NSString *)adderss age:(NSUInteger)age score:(NSUInteger)score{
    if (self = [super initWithName:name gender:gender address:adderss age:age]) {
        _score = score;
    }
    return self;
}
+(instancetype)factoryWithName:(NSString *)name gender:(NSString *)gender address:(NSString *)adderss age:(NSUInteger)age score:(NSUInteger)score{
    return [[self alloc]initWithName:name gender:gender address:adderss age:age score:score];
    
}
-(void)function{
    NSLog(@"我是一名学生，我考了%lu",(unsigned long)self.score);
}
//这时候实现NSCoding协议可以继承父类的协议方法，也可以像父类那样重新
//写。如多继承父类的，如[super copyWithZone:zone],由于父类的方法使用的
//是［self class］，这样［self class］结果便是Student类，[super copyWithZone:zone]
//结果便是Student的对象。
-(instancetype)copyWithZone:(NSZone *)zone{
    Student* student = [super copyWithZone:zone];
    student.score = _score;
    return student;
}
-(NSString*)description{
    return [[super description] stringByAppendingString:[NSString stringWithFormat:@"  score:%lu",(unsigned long)_score]];
}
@end

3.我们创建一个School类，里面有自定义Student类，然后遵循NSCoding协议

**** .h文件  ****
#import 
#import "Student.h"
@interface School : NSObject
@property(nonatomic,strong) Student * student;
@property(nonatomic,strong) NSString * address;
-(instancetype)initWithAddress:(NSString*)address student:(Student*)student;
+(instancetype)factoryWithAddress:(NSString*)address  student:(Student*)student;
@end

**** .m文件  ****
#import "School.h"
@implementation School
-(instancetype)initWithAddress:(NSString *)address student:(Student *)student{
    if (self = [super init]) {
        _address = address;
        _student = student;
    }
    return self;
}
+(instancetype)factoryWithAddress:(NSString *)address  student:(Student *)student{
    return [[self alloc]initWithAddress:address student:student];
}
//这个时候由于我们的学生已经实现了本NSCoping协议，可以直接使用copy协议，
//深复制出一样的一个对象，原来对象修改，不影响复制出来的对象
-(instancetype)copyWithZone:(NSZone *)zone{
    return [[[self class] allocWithZone:zone]initWithAddress:[_address copy]  student:[_student copy]];
    
}
-(NSString*)description{
    NSString* teacher = _teacher.description;
    NSString* student = _student.description;
    return [NSString stringWithFormat:@"\naddress:%@\nteacher:%@\nstudent:%@",_address,teacher,student];
}
@end

代码实例很简单，逻辑也是很简单的，需要注意 的地方在代码里都有注释，还有NSMutableCoping协议没有说，这个协议适合用在数组，字典等集合类型，看复制出来的对象是否可以变化。

-主要注意点

1. [self class]代替直接写类
2. [[[self class] allocWithZone:zone]initWithAddress:[_address copy] student:[_student copy]]
   在协议里复制属性时候，使用本身的copy方法，不然会出现，复制出来的实例变量会跟随复制前对象的实例变量改变而改变。就是说一定要深复制属性，不是只复制实例变量的指针。

如果有错误的地方请指正，互相学习进步