[C#] How can I associate an event handler with a 'group method'?

Question

I am trying to trigger a process when a RemoveAt(i) method is performed on an ArrayList I have defined. Can this be done? How?

Thanks,

Asaf.

Answer 1

What about using ObservableCollection instead an ArrayList? It shipped with WPF but I believe you can use it without problems if you're using .net 3.5. ObservableCollection implements INotifyCollectionChanged, so you can have access to the CollectionChanged event.

Edit: You can also create your own collection, implementing ICollection and IEnumerable, adding an ArrayList as a field and raising events around your own Add and Remove methods. Check out the solution provided by this guy.

Here's a snippet on how you can achieve what you want:

public class MyArrayList : IList, ICollection, IEnumerable, ICloneable
{
    private ArrayList arrayList = new ArrayList();

    public event System.EventHandler RemovedItem;

    public void RemoveAt(int index)
    {
     this.arrayList.RemoveAt(item);
     if (RemovedItem != null) {
      RemovedItem(this, new EventArgs());
     }
    }

    // implement required interface members...
}

Answer 2

You would need to subclass array list and override the method in order for this to work. In .Net 3.5 there is an "ObservableCollection" class which implements a CollectionChanged event which you could use if you aren't constrained to using ArrayList. ObservableCollection also implements ICollection and IEnumerable so you should be able to swap it out for ArrayList.