Events

Events are basically callbacks from GUI elements that allow us to write custom user actions. When using a GUI library, such as Windows Forms or Windows Presentation Foundation (WPF), events are part of the GUI classes. We can add custom behavior by adding a listener to these events. For example, if we want to handle the click event of a button in a login form, we can write a listener code for the Click event of that Login button.

Events in F# are first-class citizens, which means that they are exposed as a type IEvent<'T> that are composable using the Events module. Let's take a look at declaring events and using them, and then dive into using event processing in GUI programming.

Declaring events

Events are created using the F# Event<'T> class, which is a wrapper implementation around the .NET eventing system. It has the following two functions:

• Publish: This is used to expose the event
• Trigger: This triggers or raises the event with the arguments

The following piece of code...