XtAddEventHandler(3Xt)

     NAME
          XtAddEventHandler, XtAddRawEventHandler,
          XtRemoveEventHandler, XtRemoveRawEventHandler,
          XtInsertEventHandler, XtInsertRawEventHandler - add and
          remove event handlers

     SYNTAX
          void XtAddEventHandler(w, event_mask, nonmaskable, proc,
          client_data)
                Widget w;
                EventMask event_mask;
                Boolean nonmaskable;
                XtEventHandler proc;
                XtPointer client_data;

          void XtAddRawEventHandler(w, event_mask, nonmaskable, proc,
          client_data)
                Widget w;
                EventMask event_mask;
                Boolean nonmaskable;
                XtEventHandler proc;
                XtPointer client_data;

          void XtRemoveEventHandler(w, event_mask, nonmaskable, proc,
          client_data)
                Widget w;
                EventMask event_mask;
                Boolean nonmaskable;
                XtEventHandler proc;
                XtPointer client_data;

          void XtRemoveRawEventHandler(w, event_mask, nonmaskable,
          proc, client_data)
                Widget w;
                EventMask event_mask;
                Boolean nonmaskable;
                XtEventHandler proc;
                XtPointer client_data;

          void XtInsertEventHandler(w, event_mask, nonmaskable, proc,
          client_data, position)
                Widget w;
                EventMask event_mask;
                Boolean nonmaskable;
                XtEventHandler proc;
                XtPointer client_data;
                XtListPosition position;

          void XtInsertRawEventHandler(w, event_mask, nonmaskable,
          proc, client_data, position)
                Widget w;
                EventMask event_mask;
                Boolean nonmaskable;
                XtEventHandler proc;
                XtPointer client_data;
                XtListPosition position;

          typedef enum { XtListHead, XtListTail } XtListPosition;

     ARGUMENTS
          client_data
                    Specifies additional data to be passed to the
                    client's event handler.

          event_mask
                    Specifies the event mask for which to call or
                    unregister this procedure.

          nonmaskable
                    Specifies a Boolean value that indicates whether
                    this procedure should be called or removed on the
                    nonmaskable events (GraphicsExpose, NoExpose,
                    SelectionClear, SelectionRequest, SelectionNotify,
                    ClientMessage, and MappingNotify).

          proc      Specifies the procedure that is to be added or
                    removed.

          w         Specifies the widget for which this event handler
                    is being registered.

          position  Specifies when the event handler is to be called
                    relative to other previously registered handlers.

     DESCRIPTION
          The XtAddEventHandler function registers a procedure with
          the dispatch mechanism that is to be called when an event
          that matches the mask occurs on the specified widget.  If
          the procedure is already registered with the same
          client_data, the specified mask is ORed into the existing
          mask.  If the widget is realized, XtAddEventHandler calls
          XSelectInput, if necessary.

          The XtAddRawEventHandler function is similar to
          XtAddEventHandler except that it does not affect the
          widget's mask and never causes an XSelectInput for its
          events.  Note that the widget might already have those mask
          bits set because of other nonraw event handlers registered
          on it.

          The XtRemoveRawEventHandler function stops the specified
          procedure from receiving the specified events.  Because the
          procedure is a raw event handler, this does not affect the
          widget's mask and never causes a call on XSelectInput.
          XtInsertEventHandler is identical to XtAddEventHandler with
          the additional position argument. if position is XtListHead,
          the event handler is registered to that it will be called
          before any event handlers that were previously registered
          for the same widget.  If position is XtListTail, the event
          handler is registered to be called after any previously
          registered event handlers. If the procedure is already
          registered with the same client_data value, the specified
          mask augments the existing mask and the procedure is
          repositioned in the list.

          XtInsertRawEventHandler is similar to XtInsertEventHandler
          except that it does not modify the widget's event mask and
          never causes an XSelectInput for the specified events. If
          the procedure is already registered with the same
          client_data value, the specified mask augments the existing
          mask and the procedure is repositioned in the list.

     SEE ALSO
          XtAppNextEvent(3Xt), XtBuildEventMask(3Xt)
          X Toolkit Intrinsics - C Language Interface
          Xlib - C Language X Interface