Types of Events
Will Events
Event handlers called before the operation starts offer you the opportunity to examine or modify the operation parameters, and then either cancel the operation or allow it to complete. These event handler routines usually have names of the form WillEvent.
Complete Events
Event handlers called after an operation completes can notify your application that an operation has concluded. Such an event handler is also notified when a Will event handler cancels a pending operation. These event handler routines usually have names of the form EventComplete.
Will and Complete events are typically used in pairs.
Other Events
The other event handlers—that is, events whose names are not of the form WillEvent or EventComplete—are called only after an operation completes.