What is the syntax to declare an event in C#?

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; 

Answer 2

You need to specify the delegate type the event:

public event Action CollectMapsReportingComplete; 

Here I have used System.Action but you can use any delegate type you wish (even a custom delegate). An instance of the delegate type you specify will be used as the backing field for the event.