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8    Event Codes

Programming Basics

Exploring Palm OS®

The file EventCodes.h defines the Palm OS-generated events. This chapter documents that header file, and is organized as follows:

Event Codes Structures and Types
Event Codes Constants
Event Codes Events

For information on the structures that accompany most events, and the functions that can be used to manipulate the event queue, see Chapter 7, "Event." For conceptual information on events and the event queue, see Chapter 3, "Events and the Event Loop."

Event Codes Structures and Types ^TOP^

eventsEnum Typedef ^TOP^

Purpose

Defines a type that can be used to hold an event value.

Declared In

EventCodes.h

Prototype

typedef uint32_t eventsEnum

Comments

See "Event Codes Events" for the set of event values defined by Palm OS.

Event Codes Constants ^TOP^

Miscellaneous Event Codes Constants ^TOP^

Purpose

In addition to the enum that defines the events themselves, the EventCodes.h header file declares these constants.

Declared In

EventCodes.h

Constants

invalidEvent = 100
An invalid event value, used for error checking. This event is not normally posted to the event queue.
firstINetLibEvent = 0x1000
Base value for Internet Library events.
firstWebLibEvent = 0x1100
Base value for Web Library events.
firstUserEvent = 0x6000
Base value for events generated by third-party applications. All events generated by Palm OS have a value less than firstUserEvent. Third-party application event values should fall in the range:
firstUserEvent >= n >= lastUserEvent
lastUserEvent = 0x7FFF
The maximum value that should be used for an event generated by a third-party application. Third-party application event values should fall in the range:
firstUserEvent >= n >= lastUserEvent

Event Codes Events ^TOP^


NOTE: The events documented in this section represent general events of interest to most Palm OS programmers. Other events declared in EventCodes.h are generated by, or handled by, specific portions of the system and thus are only of interest to developers working with the corresponding operating system features. Those events are documented in other books in the Exploring Palm OS series, as listed under "Palm OS-Generated Events."

appStopEvent ^TOP^

Purpose

Request for the current application to terminate.

Prototype

There is no event-specific data associated with this event.

Comments

When the system wants to launch a different application than the one currently running, the event manager sends this event to request the current application to terminate. In response, an application has to exit its event loop, close any open files and forms, and exit.

If an application doesn't respond to this event by exiting, the system can't start the other application.

nilEvent ^TOP^

Purpose

Event that is sent by the Event Manager when there are no events in the event queue.

Prototype

There is no event-specific data associated with this event.

Comments

A nilEvent is useful for animation, polling, and similar situations.

The Event Manager sends this event when there are no events in the event queue. This can happen if the routine EvtGetEvent() is passed a time-out value (a value other than evtWaitForever). If EvtGetEvent() is unable to return an event in the specified time, it returns a nilEvent. Different Palm OS versions and different devices can send nilEvents under different circumstances, so you might receive a nilEvent even before the timeout has expired.

prgMakeCallback ^TOP^

Purpose

This event is for use by the operating system only. Applications should not post or act upon this event

prgUpdateDialog ^TOP^

Purpose

This event is for use by the operating system only. Applications should not post or act upon this event