//解档
- (id)initWithCoder:(NSCoder *)decoder
  {
if (self = [super init]) {
    unsigned int count = 0;
    //获取类中所有成员变量名
    Ivar *ivar = class_copyIvarList([MyModel class], &count);
      for (int i = 0; i<count; i++) {
          Ivar iva = ivar[i];
          const char *name = ivar_getName(iva);
          NSString *strName = [NSString stringWithUTF8String:name];
          //进行解档取值
          id value = [decoder decodeObjectForKey:strName];
          //利用KVC对属性赋值
          [self setValue:value forKey:strName];
      }
      free(ivar);
  }
  return self;
  }
//归档
- (void)encodeWithCoder:(NSCoder *)encoder
{
    unsigned int count;
    Ivar *ivar = class_copyIvarList([MyModel class], &count);
    for (int i=0; i<count; i++) {
        Ivar iv = ivar[i];
        const char *name = ivar_getName(iv);
        NSString *strName = [NSString stringWithUTF8String:name];
        //利用KVC取值
        id value = [self valueForKey:strName];
        [encoder encodeObject:value forKey:strName];
    }
    free(ivar);
}