注意，实现NSCoding协议不能使用extension，因为指定构造器不能声明在extension中

#import <Foundation/Foundation.h>
//实现NSCoding协议
@interface RTAutoArchive : NSObject<NSCoding>

@end

#import "RTAutoArchive.h"
#import <objc/runtime.h>

@implementation RTAutoArchive

- (void)encodeWithCoder:(NSCoder *)encoder
{
    unsigned int count = 0;
    //实例变量的列表
    Ivar *ivars = class_copyIvarList([self class], &count);
    for (int i = 0; i < count; i ++) {
        //取出i位置对应的实例变量
        Ivar ivar = ivars[i];
        //查看实例变量的名字
        const char *name = ivar_getName(ivar);
        //转化为NSString
        NSString *nameStr = [NSString stringWithCString:name encoding:NSUTF8StringEncoding];
        //利用KVC取出属性对应的值
        id value = [self valueForKey:nameStr];
        //归档
        [encoder encodeObject:value forKey:nameStr];
    }
    //释放
    free(ivars);
    
}

- (id)initWithCoder:(NSCoder *)decoder
{
    if (self = [super init]) {
        unsigned int count = 0;
        Ivar *ivars = class_copyIvarList([self class], &count);
        for (int i = 0; i < count; i ++) {
            Ivar ivar = ivars[i];
            const char *name = ivar_getName(ivar);
            NSString *key = [NSString stringWithCString:name encoding:NSUTF8StringEncoding];
            id value = [decoder decodeObjectForKey:key];
            //设值
            [self setValue:value forKey:key];
        }
        
        free(ivars);
    }
    return self;
}

@end