Volume 6A: Motif Programming Manual

RowColumn widget. In such cases, you may want to use XmNisHomogeneous and XmNentryClass. Unless

there is some way for a user to to dynamically create widgets while an application is running, these resources are not

particularly useful.

9.5.3 Callbacks

The RowColumn does not provide any specific callback routines that react to user input. While there are no callbacks

for FocusIn and FocusOut events, the widget does have XmNmapCallback and XmNunmapCallback

callback resources. These callbacks are invoked when the window for the RowColumn is mapped and unmapped. The

callbacks are similar to those for the BulletinBoard, but since the RowColumn is not designed specifically to be a

child of a DialogShell, the routines are invoked regardless of whether the parent of the RowColumn is a DialogShell.

The XmNentryCallback is the only other callback that is associated specifically with the RowColumn widget.

This callback resource makes it possible to install a single callback function that acts as the activation callback for

each of the children of a RowColumn widget. The routine specified for the XmNentryCallback overrides the

XmNactivateCallback functions for any PushButton or CascadeButton children and the

XmNvalueChangedCallback functions for ToggleButtons. The XmNentryCallback is a convenience to the

programmer; if you use it, you don't have to install separate callbacks for each widget in the RowColumn.

XmNentryCallback functions must be installed before children are added to the RowColumn, so be sure you call

XtAddCallback() before you create any child widgets.

The callback procedure takes the standard form of an XtCallbackProc. The call_data parameter is an

XmRowColumnCallbackStruct, which is defined as follows:

typedef struct {

int reason;

XEvent *event;

Widget widget;

char *data;

char *callbackstruct;

} XmRowColumnCallbackStruct;

The reason field of this data structure is set to XmCR_ACTIVATE when the XmNentryCallback is invoked. The

event indicates the event that caused the notification. The entry callback function is called regardless of which

widget within the RowColumn was activated. Since an entry callback overrides any previously−set callback lists for

PushButtons, CascadeButtons, and ToggleButtons, the parameters that would have been passed to these callback

routines are provided in the RowColumn callback structure. The widget field specifies the child that was activated,

the widget−specific callback structure is placed in the callbackstruct field, and the client data that was set for

the widget is passed in the data field.

the source code shows the installation of an entry callback and demonstrates how the normal callback functions are

overridden. XtSetLanguageProc() is only available in X11R5; there is no corresponding function in X11R4.

/* entry_cb.c −− demonstrate how the XmNentryCallback resource works

* in RowColumn widgets. When a callback function is set for this

* resource, all the callbacks for the RowColumn's children are reset

* to point to this function. Their original functions are no longer

* called had they been set in favor of the entry−callback function.

*/

#include <Xm/PushBG.h>

#include <Xm/RowColumn.h>

char *strings[] = {

"One", "Two", "Three", "Four", "Five",

9 Manager Widgets 9.5.3 Callbacks

231

"Six", "Seven", "Eight", "Nine", "Ten",

};

void

called(widget, client_data, call_data)

Widget widget;

XtPointer client_data;

XtPointer call_data;

{

XmRowColumnCallbackStruct *cbs =

(XmRowColumnCallbackStruct *) call_data;

Widget pb = cbs−>widget;

printf ("%s: %d0, XtName (pb), cbs−>data);

}

static void

never_called(widget, client_data, call_data)

Widget widget;

XtPointer client_data;

XtPointer call_data;

{

puts ("This function is never called");

}

main(argc, argv)

int argc;

char *argv[];

{

Widget toplevel, parent, w;

XtAppContext app;

int i;

XtSetLanguageProc (NULL, NULL, NULL);

toplevel = XtVaAppInitialize (&app, "Demos",

NULL, 0, &argc, argv, NULL, NULL);

parent = XtVaCreateManagedWidget ("rowcolumn",

xmRowColumnWidgetClass, toplevel,

NULL);

XtAddCallback (parent, XmNentryCallback, called, NULL);

/* simply loop thru the strings creating a widget for each one */

for (i = 0; i < XtNumber (strings); i++) {

w = XtVaCreateManagedWidget (strings[i],

xmPushButtonGadgetClass, parent, NULL);

/* Call XtAddCallback() to install client_data only! */

XtAddCallback (w, XmNactivateCallback, never_called, i+1);

}

XtRealizeWidget (toplevel);

XtAppMainLoop (app);

}

The RowColumn is created and its XmNentryCallback is set to called(). This routine ignores the

client_data parameter, as none is provided. However, we do use the data field of the cbs because this is the

data that is specified in the call to XtAddCallback() for each of the children. We install the never_called()

routine for each PushButton and pass the position of the button in the RowColumn as the client_data. Even

though the entry callback overrides the activate callback, the client_data is preserved.

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232