#381 – Implementing an Event that Returns Some Data

When you implement an event, you can define your own delegate type, or you can use the existing EventHandler or EventHandler<TEventArgs> types.

If you want your event to return some data, you should:

• Create a new class that inherits from EventArgs for the event’s data
• Use the EventHandler<TEventArgs> delegate type

Start by defining new EventArgs-based class that will store the event’s data.

    public class BarkedEventArgs : EventArgs
    {
        public string BarkSound { get; protected set; }
        public BarkedEventArgs(string barkSound)
        {
            BarkSound = barkSound;
        }
    }

Then, in your class, declare the event and a helper method to raise the event.

        // Declare the event
        public event EventHandler<BarkedEventArgs> Barked;

        // Helper method that raises the event
        protected virtual void OnBarked(string sound)
        {
            if (Barked != null)
                Barked(this, new BarkedEventArgs(sound));
        }

Finally, raise the event whenever a Dog barks.

        public void Bark(string barkSound)
        {
            Console.WriteLine(barkSound);

            OnBarked(barkSound);
        }