无法访问的上报字段

Question

How can I access a field in a UpCasted Object? I cannot use Console.WriteLine in order to print SuperPower property of a Guy object

namespace Test
{
    class Guy
    {
        public int Power { get; set; }
    }

    class BigGuy : Guy
    {
        public int SuperPower { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Guy guy = new Guy();
            BigGuy bigGuy = new BigGuy();
            bigGuy.SuperPower = 4;
            guy = bigGuy;
            Console.WriteLine(guy.SuperPower); // Visual studio doesn't accept this line.
        }
    }
}

When i debug I get an error:

'Guy' does not contain a definition for 'SuperPower' 

Why can't I access guy.SuperPower field?

Answer 1

在访问BigGuy类的字段之前，您必须将guy投给BigGuy ：

Console.WriteLine(((BigGuy)guy).SuperPower);

Answer 2

Because the type of the variable is Guy . Which means you only have access to properties declared on the Guy type.

Imagine if you had a second subclass:

class FastGuy : Guy
{
    public int SpeedPower { get; set; }
}

guy = bigGuy;
guy = new FastGuy();

The properties you would be able to access would change depending on what value you're assigning. That would mean it wouldn't be able to do type checking at compile time.

Typically, the point of declaring a type as some less specific type is so that you can act on the object as though it were that type, even though the concrete type may be a subclass.