Question

Example code:

  public class ElementList
  {
        // some code...

        public ElementList (Element owner)
        {
              // some code...
        }

        public void Add (Element e)
        {
              if (e == owner) // cannot add child which will be self-parent
              {
                    throw new SomeException (); // main problem here
              }

              childList.Add (e);
        }
  }

Now what kind of exception I should throw? And if you suggest custom exception, please tell me a good name for it.

Answer 1

In short: ArgumentException will do the trick. However, it is not a good practice to throw exceptions that you may easily managed in your code.

I would suggest to rewrite your code like:

public void Add (Element e)
        {
              if (e != owner)
              {
                  // Not the owner, do your operation
                   childList.Add (e);
              }
              else {
                    // Log error message or display warning to user
                 }              
        }

However, if you would like to proceed with exception scenario, then the code will probably look like:

if (e == owner) // cannot add child which will be self-parent
{
    throw new ArgumentException("Can not add child which will be self-parent");
}

Edit: As a reference you may of course use the MSDN article for detailed understanding.