something.m

- (void)encodeWithCoder:(NSCoder *)aCoder
{
    [super encodeWithCoder:aCoder];
    [aCoder encodeObject:_vValue forKey:@"vValue"];
}

- (id)initWithCoder:(NSCoder *)aDecoder
{
    self = [super initWithCoder:aDecoder];
    if (!self) return nil;
    
    _vValue = [[aDecoder decodeObjectForKey:@"vValue"] retain]; // don't retain in ARC
    if (/* !vValue || */ ![vValue isKindOfClass:[Whatever class]])
    {
        [self dealloc]; // not in ARC
        return nil;
    }
    return self;
}

Also helpful is my thoughtfully compiled NSCoding Tips, though it looks like you're trying to show conditional encoding (which is slightly more fun to do).