Question

In my class I want to declare an event that other classes can subscribe to. What is the correct way to declare the event?

This doesn’t work:

public event CollectMapsReportingComplete;

Answer 1

You forgot to mention the type. For really simple events, EventHandler might be enough:

public event EventHandler CollectMapsReportingComplete;

Sometimes you will want to declare your own delegate type to be used for your events, allowing you to use a custom type for the EventArgs parameter (see Adam Robinson’s comment):

public delegate void CollectEventHandler(object source, MapEventArgs args);

public class MapEventArgs : EventArgs
{
    public IEnumerable<Map> Maps { get; set; }
}

You can also use the generic EventHandler type instead of declaring your own types:

public event EventHandler<MapEventArgs> CollectMapsReportingComplete;