XtAppNextEvent(Xt)

Syntax

void XtAppNextEvent (app_context, event_return)
XtAppContext app_context;
XEvent event_return;

Boolean XtAppPeekEvent (app_context, event_return)
XtAppContext  app_context;
XEvent event_return;

XtInputMask XtAppPending (app_context)
XtAppContext app_context;

void XtAppProcessEvent (app_context, mask)
XtAppContext  app_context;
XtInputMask  mask;

Boolean XtDispatchEvent (event)
XEvent  event;

void XtAppMainLoop (app_context)
XtAppContext  app_context;

Arguments

app_context

Specifies the application context that identifies the application.

event

Specifies a pointer to the event structure that is to be dispatched to the appropriate event handler.

event_return

Returns the event information to the specified event structure.

mask

Specifies what types of events to process. The mask is the bitwise inclusive OR of any combination of XtIMXEvent, XtIMTimer, and XtIMAlternateInput. As a convenience, the XtToolkit defines the symbolic name XtIMAll to be the bitwise inclusive OR of all event types.

Description

If there is an event in the queue, XtAppPeekEvent fills in the event and returns a nonzero value. If no X input is on the queue, XtAppPeekEvent flushes the output buffer and blocks until input is available (possibly calling some timeout callbacks in the process). If the input is an event, XtAppPeekEvent fills in the event and returns a nonzero value. Otherwise, the input is for an alternate input source, and XtAppPeekEvent returns zero.

The XtAppPending function returns a nonzero value if there are events pending from the X server, timer pending, or other input sources pending. The value returned is a bit mask that is the OR of XtIMXEvent, XtIMTimer, and XtIMAlternateInput (see XtAppProcessEvent). If there are no events pending, XtAppPending flushes the output buffer and returns zero.

The XtAppProcessEvent function processes one timer, alternate input, or X event. If there is nothing of the appropriate type to process, XtAppProcessEvent blocks until there is. If there is more than one type of thing available to process, it is undefined which will get processed. Usually, this procedure is not called by client applications (see XtAppMainLoop). XtAppProcessEvent processes timer events by calling any appropriate timer callbacks, alternate input by calling any appropriate alternate input callbacks, and X events by calling XtDispatchEvent.

When an X event is received, it is passed to XtDispatchEvent, which calls the appropriate event handlers and passes them the widget, the event, and client-specific data registered with each procedure. If there are no handlers for that event registered, the event is ignored and the dispatcher simply returns. The order in which the handlers are called is undefined.

The XtDispatchEvent function sends those events to the event handler functions that have been previously registered with the dispatch routine. XtDispatchEvent returns True if it dispatched the event to some handler and False if it found no handler to dispatch the event to. The most common use of XtDispatchEvent is to dispatch events acquired with the XtAppNextEvent procedure. However, it also can be used to dispatch user-constructed events. XtDispatchEvent also is responsible for implementing the grab semantics for XtAddGrab.

The XtAppMainLoop function first reads the next incoming X event by calling XtAppNextEvent and then it dispatches the event to the appropriate registered procedure by calling XtDispatchEvent. This constitutes the main loop of XtToolkit applications, and, as such, it does not return.
Applications are expected to exit in response to some user action. There is nothing special about XtAppMainLoop; it is simply an infinite loop that calls XtAppNextEvent and then XtDispatchEvent.

Applications can provide their own version of this loop, which tests some global termination flag or tests that the number of top-level widgets is larger than zero before circling back to the call to XtAppNextEvent

See also