XtEventHandler()XtEventHandler()NameXtEventHandler - interface definition for event handler procedure.
Synopsis
typedef void (*XtEventHandler)(Widget, XtPointer, XEvent *, Boolean *);
Widget w;
XtPointer client_data;
XEvent *event;
Boolean *continue_to_dispatch_return
Inputs
w Specifies the widget for which the handler was registered.
client_data
Specifies data registered with this event handler.
event Specifies the event that triggered this call.
Outputs
continue_to_dispatch_return
Returns a Boolean indicating whether to call the remaining
event handlers that are registered for the current event.
Description
An XtEventHandler is registered with XtAddEventHandler(), XtAddRawEven‐
tHandler(), XtInsertEventHandler(), or XtInsertRawEventHandler(). It
is called when one of the events that it was registered to handle
occurs on the widget it was registered for.
An XtEventHandler should do whatever processing is necessary for the
widget or application to handle the event event that occurred on widget
w. The client_data argument can be arbitrary data registered with the
event handler procedure. It is cast to an XtPointer when registered
and should be cast back to the appropriate type within the event han‐
dler.
The continue_to_dispatch_return is the address of a Boolean variable
which is intialized to True by the Intrinsics before the event handler
is called. If a handler sets this variable to False, then no more han‐
dlers will be dispatched for the event. Doing this may lead to porta‐
bility problems because implementations of the Intrinsics are allowed
to add event handlers for any widget at any time. If you prevent these
potential "invisible" event handlers from receiving events, the Intrin‐
sics are not guaranteed to behave as expected.
Usage
Most widgets and applications do not need to use event handlers explic‐
itly. Instead they can use translation tables and action procedures.
Example
The procedure below is an event handler from the xmag client. It is a
special handler that follows the location of the mouse while it is
dragged with the button down and a pointer grab is in effect. When
the button is released, it magnifies a new area of the screen, releases
the pointer grab, and calls XtRemoveEventHandler() on itself.
/*
* ResizeEH()-- Event Handler for resize of selection box.
*/
static void
ResizeEH(w, closure, event, continue_to_dispatch) /* ARGSUSED */
Widget w; XtPointer closure; XEvent *event; Boolean *continue_to_dispatch;
{
hlPtr data = (hlPtr)closure;
switch (event->type) {
case MotionNotify:
data->x = event->xmotion.x_root;
data->y = event->xmotion.y_root;
break;
case ButtonRelease:
GetImageAndAttributes(FindWindow(event->xmotion.x_root,
event->xmotion.y_root),
min(data->homeX,event->xbutton.x_root),
min(data->homeY,event->xbutton.y_root),
abs(data->homeX - event->xbutton.x_root),
abs(data->homeY - event->xbutton.y_root),
data);
if (data->newScale)
PopupNewScale(data);
else
SWSetImage(data->scaleInstance, data->image);
XtUngrabPointer(w, CurrentTime);
XtRemoveEventHandler(w, PointerMotionMask ButtonReleaseMask,
True, ResizeEH, (XtPointer)data);
data->selectMode = done;
break;
}
}
This event handler is registered with the following code, invoked when
the user presses mouse button 2.
XtAddEventHandler(w, PointerMotionMask ButtonReleaseMask,
True, ResizeEH, (XtPointer)data);
See AlsoXtAddEventHandler(1), XtAddRawEventHandler(1), XtAppAddActions(1),
XtRemoveEventHandler(1), XtRemoveRawEventHandler(1).
Xt - Event Handling XtEventHandler()
