Type casting question

Question

foreach(PlayerBase p in Members)
{
    p.Render();
}

The Members list contains members of type FieldPlayer or GoalKeeper. FieldPlayer and GoalKeeper inherit from PlayerBase. When I call p.Render(), I need the appropriate Render call to be called for FieldPlayer or GoalKeeper. How do I do that?

Thanks

Answer 1

You make the PlayerBase.Render method virtual. See this question for more information.

Answer 2

You're talking about Polymorphism. The proper implementation of Render is automatically called. Make sure the Render method in your PlayerBase class is defined as either abstract or virtual.

Answer 3

If FieldPlayer and GoalKeeper override the Render method, then this will happen automatically.

public abstract class PlayerBase
{
    public virtual void Render();
}

public class FieldPlayer : PlayerBase
{
    public override void Render() {...}
}

Answer 4

If PlayerBase is an interface

public inteface IPlayerBase 
{
   void Render();
}

public class FieldPlayer : IPlayerBase
{
   public void Render()
   {
      MessageBox.Show("FieldPlayer.Render");
   }
}

public class GoalKeeper : IPlayerBase
{
   public void Render()
   {
      MessageBox.Show("GoalKeeper.Render");
   }
}

If PlayerBase is an abstract class

public abstract class PlayerBase 
{
   public abstract void Render();
}

public class FieldPlayer : PlayerBase
{
   public override void Render()
   {
      MessageBox.Show("FieldPlayer.Render");
   }
}

public class GoalKeeper : PlayerBase
{
   public override void Render()
   {
      MessageBox.Show("GoalKeeper.Render");
   }
}

If PlayerBase is an class with a virtual function

public class PlayerBase 
{
   public virtual void Render()
   {
      MessageBox.Show("PlayerBase.Render");
   }
}

public class FieldPlayer : PlayerBase
{
   public override void Render()
   {
      MessageBox.Show("FieldPlayer.Render");
   }
}

public class GoalKeeper : PlayerBase
{
   public override void Render()
   {
      MessageBox.Show("GoalKeeper.Render");
   }
}

For all three instances, the derived type's Render function will be called.

Answer 5

If Render is a virtual member, then the method called will be that on the most derived type of the object at runtime.

Answer 6

You should declare Render on PlayerBase to be either virtual (if you have a default implementation) or abstract. Then, you override the method in the child classes with the desired behavior.

Answer 7

You can mark Render as abstract and then every derived class must implement it.

See this for more information: http://msdn.microsoft.com/en-us/library/ms173152%28v=vs.80%29.aspx

Answer 8

abstract class PlayerBase
{
    public abstract void Render();
}

Any class that inherits PlayerBase will be required to implement the Render function. If you have common functionality for Render, you can instead:

abstract class PlayerBase
{
    public virtual void Render() {
        // add common functionality
    }
}

Then in your sub-class, say FieldKeeper:

class FieldKeeper : PlayerBase    {
    public override void Render() {
        // add additional functionality
        base.Render();
    }
}