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Abstract base class ..... in C#?


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#1 Alpha_ProgDes   Crossbones+   -  Reputation: 4692

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Posted 10 September 2013 - 04:37 PM

I must be getting my languages confused...
 
Here's what I want to do in C#
 

//create an interface
public interface IAdd
{
   public int moveXUnits(int XUnits);
}

//create an abstract base class that inherits the interface
public abstract class Movement : IAdd
{
   private int startUnit;

   public Movement()
   {
      startUnit = 0;
   }

   public Movement(int initializeUnit)
   {
      startUnit = initializeUnit;
   }

   public int moveXUnits(int XUnits)
   {
      startUnit += XUnits;
      return startUnit;
   }
}
 
//finally create some concrete classes that inherits from the abstract base class
public class Walk : Movement
{
   base(1);
   public void Step()
   {
      moveXUnits(2);
   }
}

public class Skip : Movement
{
   base(2);
   public void Step()
   {
      moveXUnits(3);
   }
}

public class Run:Movement
{
   base(3);
   public void Step()
   {
      moveXUnits(5);
   }
}

 
So my first question is: what is the analogous keyword for base in C#. Because 'base' is giving me an error.
Second question is: is this right? I have a feeling that it isn't.


Edited by Alpha_ProgDes, 10 September 2013 - 04:39 PM.

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#2 SiCrane   Moderators   -  Reputation: 9670

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Posted 10 September 2013 - 04:53 PM

What are those base() calls meant to do? Call the base class constructor? In that case you need to make the calls as part of the derived class constructors. Ex:
Walk() : base(1) {}


#3 Alpha_ProgDes   Crossbones+   -  Reputation: 4692

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Posted 10 September 2013 - 05:04 PM

What are those base() calls meant to do? Call the base class constructor? In that case you need to make the calls as part of the derived class constructors. Ex:

Walk() : base(1) {}

 

You're exactly right. On both points.

 

Though it's a simple example, any other improvements would be much appreciated.


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#4 unbird   Crossbones+   -  Reputation: 6016

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Posted 10 September 2013 - 05:08 PM

I think you want Step to be in the abstract too, and then override in the derived ones, e.g.
 

public abstract class Movement : IAdd
{
   private int startUnit;

   public Movement()
   {
       startUnit = 0;
   }

   public Movement(int initializeUnit)
   {
      startUnit = initializeUnit;
   }

   public int moveXUnits(int XUnits)
   {
      startUnit += XUnits;
      return startUnit;
   }
    public abstract void Step();
}

public class Walk : Movement
{
    public Walk() : base(1) { }
    public override void Step()
    {
       moveXUnits(2);
    }
}
// etc.
And I wonder if you actually need the interface here.

#5 Alpha_ProgDes   Crossbones+   -  Reputation: 4692

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Posted 10 September 2013 - 06:11 PM

Improved code.... (I think)
   public interface IAdd
    {
        int moveXUnits(int XUnits);
    }

    public abstract class Movement : IAdd
    {
        private int startUnit;
        private int stepUnits;
        private int totalSteps;

        public Movement()
        {
            startUnit = 0;
            stepUnits = 1;
            totalSteps = 0;
        }

        public Movement(int initializeUnit, int initializeStep)
        {
            startUnit = initializeUnit;
            stepUnits = initializeStep;
            totalSteps = startUnit;
        }

        public int moveXUnits(int XUnits)
        {
            stepUnits = XUnits;
            totalSteps += stepUnits;
            return totalSteps;
        }

        private int autoMoveXUnits()
        {
            totalSteps += stepUnits;
            return totalSteps;
        }

        public virtual void Step(int XUnits)
        {
            moveXUnits(XUnits);
        }

        public virtual void Step()
        {
            autoMoveXUnits();
        }

        public virtual void displaySteps()
        {
            Console.WriteLine("I have moved " + totalSteps.ToString() + " units.");
        }
    }

    public class Walk : Movement
    {
        public Walk() : base(1,2){}
    }

    public class Skip : Movement
    {
        public Skip() : base(2,3){}
    }

    public class Run : Movement
    {
        public Run() : base(3,5){}
    }

Edited by Alpha_ProgDes, 10 September 2013 - 06:14 PM.

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#6 unbird   Crossbones+   -  Reputation: 6016

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Posted 10 September 2013 - 06:29 PM

Sure, but why polymorphism at all then ? If you can change behavior with different init values alone, no need for derived classes wink.png

#7 Starnick   Members   -  Reputation: 1254

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Posted 10 September 2013 - 06:34 PM

The IAdd interface to me is kind of weird, you're modeling a behavior (imo a good thing when it comes to interfaces), but it feels like two of the same behaviors...one as an abstract class and the other as an interface (Step vs moveXUnit), which basically are two differently named ways of doing the same exact thing. To me, if you want to define behaviors like "Move along X axis", "Move along y axis", "Move along x/y", those would be individual interfaces that something like Movement would implement. In that case, what would "Step" mean? Just feels redundant and muddying behavior.

 

Simple example granted, but defining behaviors like that in this way is kind of restricting in my opinion too. You may be able to skip, run, and hop, but that's the manner of how you do it (e.g. speed and other influences like hopping up and down), those behaviors don't need to care where you're moving. So Movement to me sounds like it should model how you're moving, and it gets used by, or itself operates on another object (interface) that models where you're moving.


Edited by Starnick, 10 September 2013 - 06:36 PM.


#8 Alpha_ProgDes   Crossbones+   -  Reputation: 4692

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Posted 10 September 2013 - 06:43 PM

Please see my other thread to see why I did all this in the first place.


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#9 Slowvomit   Members   -  Reputation: 128

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Posted 13 September 2013 - 06:06 PM

I understand that its a arbitrary example to learn the strategy pattern. But it is not aptly applied. The strategy pattern is a way to encapsulate algorithms and make them easily interchangeable. You would never use a design pattern for something as trivial as movement speed and animation change.
Movement can however be aptly applied to a strategy pattern example using your movement types:
public class Program
{
    public static void Main()
    {
        //game initialize phase:
        //constructing the objects in our game
        GameObject[] movingObjects = new GameObject[10]; 
        for(int i = 0; i < movingObjects.Length; i++)
        {
            movingObjects[i] = new movingObject();
            movingObjects[i].SetMoveStrategy(new BasicMovement());
        }
        //set object 1 to use astar
        movingObjets[1].SetMoveStrategy(new AStarMovement);
 
        //game update phase:
        //showcasing polymorphysism
        //we don't care which movement algorithm is selected for the game objects we simply want them all to move.
        for(int i = 0; i < movingObjects.Length; i++)
        {
             movingObject.Move(MovementType.Walk);
        }
    }
}
 
public class GameObject //context of strategy pattern
{ 
    private MovementStrategy movementStrategy;
 
    public void SetMoveStrategy(MovementStrategy movementStrategy)
    {
         this.movementStrategy = movementStrategy;
    }
 
    public void Move(MovementType movementType)
    {
         movementStrategy.Move(movementType);
    }
}
 
public enum MovementType
{
    Skip,
    Walk,
    Run
}
 
public abstract class MovementStrategy //interface of strategy pattern
{
    public abstract void Move();
}
 
public class BasicMovement : MovementStrategy //concrete strategy
{
    public override void Move(MovementType movementType)
    {
        //Basic Movement algorithm here, differentiate by movement type.
    }
}
 
public class BreadCrumbMovement : MovementStrategy //concrete strategy
{
    public override void Move(MovementType movementType)
    {
         //Bread Crumb algorithm here, differentiate by movement type.
    }
}
 
public class AStarMovement : MovementStrategy //concrete strategy
{
    public override void Move(MovementType movementType)
    {
         //A Star algorithm here, differentiate by movement type.
    }
}
 
The base keyword is not used at all to demonstrate the strategy pattern. It is used for "inheriting" constructor arguments passed to the base class or to reference it implicitly.

Edited by Slowvomit, 13 September 2013 - 07:29 PM.





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