如何从包含父对象的列表中调用派生类的方法？

Question

I am making a game that has an inventory system. The inventory system can contain any WorldObject . There are a number of derived classes from WorldObject that will be held within the inventory.

public class WorldObject
{
    public virtual void SomeMethod();
}

public class Weapon : WorldObject
{
    public override void SomeMethod();
}

public class Tool: WorldObject
{
    public override void SomeMethod();
}

and the inventory:

public class Inventory
{
    public List<WorldObject> ObjectList;

    public Inventory()
    {
        ObjectList = new List<WorldObject>();
    }

    public void AddToInventory(WorldObject object)
    {
        ObjectList.Add(object);
    }

    public void Foo(int itemIndex)
    {
        Weapon weaponObject = ObjectList[itemIndex] as Weapon;
        if(weaponObject != null)
        {
            weaponObject.SomeMethod();
        }
        else
        {
            Tool toolObject = ObjectList[itemIndex] as Tool;
            if(toolObject != null)
            {
                toolObject.SomeMethod();
            }
        }
    }
}

So, is there a better way to call the child methods on each of my items? This seems like a lot of headache as my game gets larger. Having 10+ different ways to do the same thing seems wrong.

Answer 1

Well, that's why SomeMethod is virtual, you know? So simply:

WorldObject obj = ObjectList[itemIndex];
obj.SomeMethod();

will do what you want — call the override of SomeMethod in the correct ancestor.

You can read the basics on Wikipedia, for example.

Answer 2

It's enough to call this method in this way:

ObjectList[itemIndex].SomeMethod();

And correct your WorldObject class to

public class WorldObject
{
    public virtual void SomeMethod() {}
}

or

public abstract class WorldObject
{
    public abstract void SomeMethod();
}

Answer 3

Since SomeMethod is virtual, just call it on the object you get from ObjectList[itemIndex] . C# will call the base (no-op) method if the object is just a WorldObject , or the appropriate override of it if the object is one of the derived classes. Read about polymorphism on MSDN.