A notification is a signal from the operating system that an event has occurred. When an application is registered for a specific event notification, the system generates a notification when that event occurs. The H/PC shell uses notifications to communicate with the user and with other Windows CE-based applications. The notification functions and structures are grouped into a notification API that is particularly useful for applications that run on a mobile device.
Windows CE generates two types of notifications, user and application. A user notification alerts the user about a timer event. For example, the system might display a dialog box and play a sound before a scheduled appointment. The notification alerts the user so that he or she can perform some action. User notifications are always associated with an application, but the application is not started until the user takes some action.
An application notification starts an application when either a timer event or a system event occurs. When the system starts an application as a result of a notification, the system specifies a command-line parameter that identifies the event that has occurred.
User notifications and application notifications have several differences. User notifications alert the user, are generated only by timer events, and are executed entirely by the operating system. The application is started only when the user responds to the notification. In contrast, application notifications may or may not involve the user, can be generated by timer or system events, and always involve the system starting an application.
The two types of events used in notifications are timer events and system events. A timer event indicates that a specified time has arrived. A system event is a system occurrence, such as establishing a network connection or changing a device. A timer event would typically be used for a calendar or a to-do-list application.