initialize_hook() initialize_hook()
Name
initialize_hook - obsolete Object method for initializing subpart data.
Synopsis
typedef void (*XtArgsProc)(Widget, ArgList, Cardinal *);
Widget w;
ArgList args;
Cardinal *num_args;
Inputs
w Specifies the newly created widget.
args Specifies the argument list that was passed to XtCreateWidget().
num_args Specifies the number of arguments in the argument list.
Availability
Obsolete in Release 4 and later.
Description
The initialize_hook() method is registered on the initialize_hook field of the Object, RectObj, or Core class part structure, and is called
by XtCreateWidget().
As of Release 4, the initialize_hook() method is obsolete because all of its arguments are now passed to the initialize() method. Its pur-
pose had been to allow the widget class to use the argument list to initialize fields that did not appear in the class resource list, by
calling XtSetSubvalues(), for example.
The initialize_hook() method is chained in superclass-to-subclass order and is called for compatibility with older widgets. It cannot be
inherited and new widgets should set their initialize_hook field to NULL. See XtCreateWidget(1) for details on when it is called. See
initialize(4) for more information on initializing subparts or other fields that do not appear in the class resource list.
See AlsoXtCreateWidget(1), XtSetSubvalues(1),
Core(3),
get_values_hook(4), set_values_hook(4), initialize(4).
Xt - Intrinsics Methods initialize_hook()
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get_values_hook() get_values_hook()
Name
get_values_hook - Object class method for obtaining values of resources that do not appear in the resource list.
Synopsis
typedef void (*XtArgsProc)(Widget, ArgList, Cardinal *);
Widget w;
ArgList args;
Cardinal *num_args;
Inputs
w Specifies the widget or object that is having its resources queried.
args Specifies the argument list that was passed to XtGetValues().
num_args Specifies the number of arguments in the argument list.
Description
The get_values_hook() method is registered on the get_values_hook field of the Object, RectObj, or Core class part structure, and is called
by XtGetValues() to give the widget a chance to supply the value of any resources that do not appear in the widget's resource list (by
calling XtGetSubvalues() on a subpart, for example) or to modify any of the returned values.
The get_values_hook() method is chained in superclass-to-subclass order, and cannot be inherited. Classes that do not need a
get_value_hook() method should specify NULL in the get_values_hook field of their class structure.
See XtGetValues(1) for more information on when this method is invoked.
Usage
If a widget or object has subparts with resources that do not appear in the resource list of the object itself, it can use the get_val-
ues_hook() method to call XtGetSubvalues() passing a pointer to the subpart, the subpart resource list, and the args and num_args argument
list. Using this technique, the application programmer will be able to query the value of subpart resources as if they were normal widget
resources.
Note that since the Object class was added in Release 4, it is often easier to use objects rather than subparts, because objects get more
automatic resource handling by the Intrinsics than subparts do. A get_values_hook() procedure is not limited to calling XtGetSubvalues();
it can call XtGetValues() on a widget or object, as shown in the examples below. When using objects rather than subparts, it is also pos-
sible to give the application programmer direct control over creating those objects. If the programmer keeps a pointer to the created
object, then she can directly set and query the resource values of the object, and no get_values_hook() is necessary in the parent.
The get_values_hook() method can also be used to modify the resource values in args that would otherwise be returned to the user. A widget
that displays a string, for example, might want to return a copy of that string to the programmer rather than the string itself, so that if
the programmer modifies the string, the widget will not be affected. Widgets that use the get_values_hook() method in this way should be
sure to document which resources are copied in this way and must be freed by the user. (None of the Intrinsics widgets nor the Xaw widgets
do this.)
Note that the get_values_hook() method is not obsolete as are the other hook methods, initialize_hook() and set_values_hook().
Example
The two procedures below are the get_values_hook() methods of the Xaw Dialog and Xaw Text widget classes. Note that both use XtGetValues()
to obtain resources of a child widget or object, which they "export" as one of their own resources.
The Dialog method checks the incoming argument list for a resource named XtNvalue, and only queries the child for that single resource.
The Text method simply passes the entire argument list in XtGetValues() calls to two different child objects. This method assumes that the
Text widget and its two children objects do not have any resources by the same name, so there is not potential for name conflicts. The
Text widget controls the types of its subobjects, so this is a reasonable assumption. Since all objects have an XtNdestroyCallback
resource, however, if you were to query the value of this resource for the Text widget, you would get the callback list for one of its
internal objects instead. (This is not a practical problem because the callback list is in an internal compiled form and should not be
queried anyway.)
static void
GetValuesHook(w, args, num_args)
Widget w;
ArgList args;
Cardinal * num_args;
{
Arg a[1];
String s;
DialogWidget src = (DialogWidget) w;
register int i;
for (i=0; i < *num_args; i++)
if (streq(args[i].name, XtNvalue)) {
XtSetArg(a[0], XtNstring, &s);
XtGetValues(src->dialog.valueW, a, 1);
*((char **) args[i].value) = s;
}
}
static void
GetValuesHook(w, args, num_args)
Widget w;
ArgList args;
Cardinal * num_args;
{
XtGetValues( ((TextWidget) w)->text.source, args, *num_args );
XtGetValues( ((TextWidget) w)->text.sink, args, *num_args );
}
See AlsoXtGetSubvalues(1), XtGetValues(1),
Core(3).
Xt - Intrinsics Methods get_values_hook()