C#

Collin Jasnoch wrote:

not virtual. That is for overloading

public void Walk()
{
  // Do walking stuff
  WalkInternal();
}

protected abstract void WalkInternal();

public abstract class Animal
{
  public void Walk()
  {
    Console.WriteLine("Starting the legs off now...");
    OnWalk();
  }

  protected abstract void OnWalk();
}

Member 8209737 wrote:

can someone give me some pointer as to go about this ?

Member 8209737 wrote:

can someone give me some pointer as to go about this ?

class SomeAnimalClass
{
    public event EventHandler IsWalkin;

    protected virtual void OnWalk()
    {
        Console.WriteLine("Doing walking stuff for " + this.GetType().Name);

        EventHandler isWalkin = IsWalkin;
        if (isWalkin != null)
        {
            isWalkin(this, EventArgs.Empty);
        }
        else
            throw new NotImplementedException("DoWalk isn't implemented in " + this.GetType().Name);
    }

    public void StartWalkin()
    {
        // point in code that's calling the custom Walk-method;
        OnWalk();
    }
}
class Cat: SomeAnimalClass { }
class Dawg: SomeAnimalClass { }

class Program
{
    static void Main(string[] args)
    {
        SomeAnimalClass animal = new Cat();
        animal.IsWalkin += (o, s) => 
            Console.WriteLine("specific walking stuff for this animal of type " + animal.GetType().Name);
        animal.StartWalkin();

        SomeAnimalClass otherAnimal = new Dawg();
        try
        {
            otherAnimal.StartWalkin();
        }
        catch (NotImplementedException nie)
        {
            Console.WriteLine(nie.Message);
        }
        Console.ReadKey();
    }
}

Doing walking stuff for Cat
specific walking stuff for this animal of type Cat
Doing walking stuff for Dawg
DoWalk isn't implemented in Dawg

Bastard Programmer from Hell

1. You want polymorphic behaviour, but the base class doesn't know what that might be. This is what abstract methods are for.
2. You want to allow subclasses to provide behaviour, but the base class has some idea what it a sensible default. For this you should use a virtual method, even if the default action is nothing.
   

   public virtual void Walk(){}

3. You know what the basic template for behaviour is, but you want subclasses to be able to customise parts of it, or you are missing information. I tend to do this with the 'MethodName'/'MethodNameInner' approach, where MethodNameInner is usually protected abstract, but if there is a reasonable default (often empty), it can be protected virtual instead.
   

   public void Walk(){
    Leg legToMove = LegToWalkWith;
    legToMove.MoveForward();
   }
   
   protected abstract Leg LegToWalkWith { get; }

   
   
   or more realistically (pseudocode as I can't remember exactly how this works right now):
   
   

   public void ReadConfig(string configFile){
    XmlDocument xmlDoc = GetXmlDocument(configFile); // don't worry about this
    XmlElement elem = xmlDoc.GetElement(ConfigNodeXpath);
    foreach(XmlNode node in elem.ChildNodes){
     XmlElement subelem = node as XmlElement;
     if(subelem == null) continue;
     // ... etc, e.g. set property by reflection
    }
   }
   
   protected abstract string ConfigNodeXpath { get; }