Raising and handling events

Methods are often described as actions that an object can perform, either on itself or on related objects. For example, List<T> can add an item to itself or clear itself, and File can create or delete a file in the filesystem.

Events are often described as actions that happen to an object. For example, in a user interface, Button has a Click event, a click being something that happens to a button, and FileSystemWatcher listens to the filesystem for change notifications and raises events like Created and Deleted that are triggered when a directory or file changes.

Another way of thinking of events is that they provide a way of exchanging messages between two objects.

Events are built on delegates, so let's start by having a look at what delegates are and how they work.

Calling methods using delegates

You have already seen the most common way to call or execute a method: use the . operator to access the method using its name...