Event Hanlder

EventHanlderTest.cs

class C
{
    public event EventHandler<EventArgs> ItemDiscarded;

    public void Add(int value)
    {
        OnItemDiscarded(value);//trigger event handler
    }

    void OnItemDiscarded(int value)
    {
        if (ItemDiscarded != null)
        {
            var arg = new ItemDiscardedEventArgs(value);
            ItemDiscarded(this, arg);
        }
    }
}

public class ItemDiscardedEventArgs : EventArgs
{
   public int ItemDiscarded {get; set;}

   public ItemDiscardedEventArgs(int item)
   {
     ItemDiscarded  = item;
   }
}

static void Main()
{
     C c = new C();
     c.ItemDiscarded += OnItemDiscarded; ;
     c.Add(5);
}

private void OnItemDiscarded(object sender, EventArgs e)
{
    var a = e as ItemDiscardedEventArgs;
    var value = a.ItemDiscarded;
}
//Covariance = <out T> returns output   (Manager -> Employe -> Person) ex: FindAll() or FindById
//Contravariance = <in T> input   (Manager -> Employe -> Person) ex:Create(),Save(),Commit();