C# How to trigger an event when a static Arraylist count is changed?

Question

I have a static array list in class called cart, is there a way to implement event listener to be used by other classes? I am new to c# tried to understand PropertyChangedEventHandler with no success. The arraylist and property are initialized as below:

private static ArrayList cartList = new ArrayList();

    public static ArrayList CartList
    {
        get { return cartList; }
        set
        {
            cartList = value;
        }
    }

Edit:

Altered @KMC code to work with List by hiding base methods:

public class ListOfProducts : List<Product>
{

    public void Add(Product obj)
    {
        base.Add(obj);
        this.OnChange();
    }

    public void UpdateLast(Product obj)
    {
        base[base.Count - 1] = obj;
        this.OnChange();
    }
    public void Remove(Product obj)
    {
        base.Remove(obj);
        this.OnChange();
    }

    public void Clear()
    {
        base.Clear();
        this.OnChange();
    }

    public event EventHandler Change;

    protected void OnChange()
    {
        if (this.Change != null)
        {
            this.Change(this, new EventArgs() { });
        }
    }
}

Answer 1

You can't get notified when count of elements in ArrayList changes nor when any element changes.

ArrayList and most other standard collections in .Net Framework like List<T> , Dictionary and arrays (except specialized classes like ObservableCollection in WPF) do not provide notification on items added/removed. You can easily check that by looking at MSDN entry for corresponding class and see if it implements INotifyCollectionChanged and/or INotifyPropertyChanged . Ie ArrayList only implements IList, ICollection, IEnumerable, ICloneable and no notification interfaces.

If you need notification of such change you should create your own class with such notification or use ObservableCollection .

Side note: please consider using List<T> instead of non-generic ArrayList - ArrayList vs List<> in C# .

Answer 2

the ArrayList type is extensible. you can override the add and remove methods and fire some events.

for ex)

public class NewArrayList : ArrayList 
{
    public event EventHandler Change; 

    public override int Add(object value)
    { 
       var result = base.Add(value);
        this.OnChange();
        return result;
    }

    public override void Remove(object obj)
    {
        base.Remove(obj);
        this.OnChange();
    }

    protected void OnChange()
    {
        if (this.Change != null)
        {
            this.Change(this, new EventArgs() { });
        }
    }
}
public static class program
{ 
    static void Main(string[] args)
    {

        var list = new NewArrayList();
        list.Change += delegate (object sender, EventArgs arg) {
            Console.WriteLine("collect changed {0}", list.Count);
        };

        list.Add(1);
        list.Add(2);
        list.Remove(2);

    }  

}

since the ArrayList needs to send some type of message (event) and I'm not sure who will be receiving it, I'll leave it up to you.