如何区分亚型？

Question

Assume we have a collection of vehicles. The vehicles may be a bicycle, motorbike or car.

Now every car in this collection should have its windows cleaned.

There is a WindowCleaner that receives this collection of vehicles. How can he tell which vehicle needs its windows cleaned? I see that if I differentiate between the vehicle subtypes in the WindowCleaner I will violate the open-closed principle.

How else could one do this? Introduce an abstract bool property NeedsWindowsCleaned and then cast to the subtype? This looks to me like type introspection in disguise.

Answer 1

using System;
using System.Collections.Generic;

namespace Dirty
{
    class Program
    {
        static void Main()
        {
            var vehicles = new List<Vehicle>();

            var bike = new Bicycle();
            var motorbike = new Motorbike();
            var car = new Car();

            vehicles.Add(bike);
            vehicles.Add(motorbike);
            vehicles.Add(car);

            foreach (var v in vehicles)
            {
                if (v.CleanWindows())
                {
                    Console.WriteLine("{0}", v);
                }
            }

            Console.ReadKey();
        }
    }

    class Vehicle
    {
        public virtual bool CleanWindows()
        {
            return false;
        }
    }

    class Bicycle : Vehicle
    {

    }

    class Motorbike : Vehicle
    {

    }

    class Car : Vehicle
    {
        public override bool CleanWindows()
        {
            return true;
        }
    }
}

I think this might do what you are after - all the classes inherit from "Vehicle" & can optionally override the virtual "CleanWindows" method ... if they don't they get the default "false"

I hope I haven't misunderstood - I am new to all this :)