Question

I have a user control that will handle images on a form. But depending on what the source is (web cam or ID scan or other video source) the user control is different.

But they share some common features so I want to create a base class.

My other controls all have some interface items that I need. I would like to declare the interface at the base level though and just implement at the class level. But virtual and override seems to be the closest way to get what I want. Is there any to do it, force the new class to implement the interface assigned at the base class? Looking around it look like making the class abstract (which I don’t fully understand) might be a start. If it was just methods that might be alright, but I am also using properties. In that area I have hit a dead end in my searches for answers. Here is what I have so far. Am I on the right track? I just have not worked with abstract classes at all and only limited exposure to interfaces. From the research I think I have the method correct just not sure about the property.

  public interface RequiredAnswer
  {
    void LabelRequiredFieldEmpty();
    bool AnswerRequired{ get;}
  }


  public abstract partial class ExtImage : UserControl, RequiredAnswer
  {
    public virtual bool AnswerRequired
    {
      get
      {
         throw new NotImplementedException ("Answer Required");
      }
    }
    public abstract void LabelRequiredFieldEmpty ()
    {
        //checkBox_AgreementAcceptedText.ForeColor = Color.Red;
    }

So I would have a class

  public partial class ExtImageWebCam : ExtImage
  {
    public override bool AnswerRequired
    {
      get
      {
        return valueFromThisClassThatMeansAnAnswerIsRequired;
      }
    }

     public override void LabelRequiredFieldEmpty ()
     {
       // do something 
     }    
  }

Answer 1

First of all, interfaces should start with an I by convention, so your interface would be IRequiredAnswer.

Second, if you want to force the inherited classes to implement their own methods rather than inheriting them, just make them abstract in the base class:

public abstract class ExtImage : UserControl, IRequiredAnswer
{
    public abstract bool AnswerRequired  { get; }

    public abstract void LabelRequiredFieldEmpty ();
}

Your child classes would then have to implement the method and property.