XtCreateWidget(3Xt)
NAME
XtCreateWidget, XtVaCreateWidget, XtCreateManagedWidget,
XtVaCreateManagedWidget, XtDestroyWidget - create and
destroy widgets
SYNTAX
Widget XtCreateWidget(name, widget_class, parent, args,
num_args)
String name;
WidgetClass widget_class;
Widget parent;
ArgList args;
Cardinal num_args;
Widget XtVaCreateWidget(name, widget_class, parent, ...)
String name;
WidgetClass widget_class;
Widget parent;
Widget XtCreateManagedWidget(name, widget_class, parent,
args, num_args)
String name;
WidgetClass widget_class;
Widget parent;
ArgList args;
Cardinal num_args;
Widget XtVaCreateManagedWidget(name, widget_class, parent,
...)
String name;
WidgetClass widget_class;
Widget parent;
void XtDestroyWidget(w)
Widget w;
ARGUMENTS
args Specifies the argument list to override the
resource defaults.
name Specifies the resource name for the created wid-
get, which is used for retrieving resources and,
for that reason, should not be the same as any
other widget that is a child of same parent.
num_args Specifies the number of arguments in the argu-
ment list.
parent Specifies the parent widget.
w Specifies the widget.
widget_class
Specifies the widget class pointer for the
created widget.
... Specifies the variable argument list to override
the resource defaults.
DESCRIPTION
The XtCreateWidget function performs much of the boiler-
plate operations of widget creation:
+o Checks to see if the class_initialize procedure has
been called for this class and for all superclasses
and, if not, calls those necessary in a superclass-
to-subclass order.
+o Allocates memory for the widget instance.
+o If the parent is a subclass of constraintWidgetClass,
it allocates memory for the parent's constraints and
stores the address of this memory into the con-
straints field.
+o Initializes the core nonresource data fields (for
example, parent and visible).
+o Initializes the resource fields (for example, back-
ground_pixel) by using the resource lists specified
for this class and all superclasses.
+o If the parent is a subclass of constraintWidgetClass,
it initializes the resource fields of the constraints
record by using the constraint resource list speci-
fied for the parent's class and all superclasses up
to constraintWidgetClass.
+o Calls the initialize procedures for the widget by
starting at the Core initialize procedure on down to
the widget's initialize procedure.
+o If the parent is a subclass of compositeWidgetClass,
it puts the widget into its parent's children list by
calling its parent's insert_child procedure. For
further information, see Section 3.5.
+o If the parent is a subclass of constraintWidgetClass,
it calls the constraint initialize procedures, start-
ing at constraintWidgetClass on down to the parent's
constraint initialize procedure.
Note that you can determine the number of arguments in an
argument list by using the XtNumber macro. For further
information, see Section 11.1.
The XtCreateManagedWidget function is a convenience rou-
tine that calls XtCreateWidget and XtManageChild.
The XtDestroyWidget function provides the only method of
destroying a widget, including widgets that need to
destroy themselves. It can be called at any time, includ-
ing from an application callback routine of the widget
being destroyed. This requires a two-phase destroy pro-
cess in order to avoid dangling references to destroyed
widgets.
In phase one, XtDestroyWidget performs the following:
+o If the being_destroyed field of the widget is True,
it returns immediately.
+o Recursively descends the widget tree and sets the
being_destroyed field to True for the widget and all
children.
+o Adds the widget to a list of widgets (the destroy
list) that should be destroyed when it is safe to do
so.
Entries on the destroy list satisfy the invariant that if
w2 occurs after w1 on the destroy list then w2 is not a
descendent of w1. (A descendant refers to both normal and
pop-up children.)
Phase two occurs when all procedures that should execute
as a result of the current event have been called (includ-
ing all procedures registered with the event and transla-
tion managers), that is, when the current invocation of
XtDispatchEvent is about to return or immediately if not
in XtDispatchEvent.
In phase two, XtDestroyWidget performs the following on
each entry in the destroy list:
+o Calls the destroy callback procedures registered on
the widget (and all descendants) in post-order (it
calls children callbacks before parent callbacks).
+o If the widget's parent is a subclass of compositeWid-
getClass and if the parent is not being destroyed, it
calls XtUnmanageChild on the widget and then calls
the widget's parent's delete_child procedure (see
Section 3.4).
+o If the widget's parent is a subclass of
constraintWidgetClass, it calls the constraint
destroy procedure for the parent, then the parent's
superclass, until finally it calls the constraint
destroy procedure for constraintWidgetClass.
+o Calls the destroy methods for the widget (and all
descendants) in post-order. For each such widget, it
calls the destroy procedure declared in the widget
class, then the destroy procedure declared in its
superclass, until finally it calls the destroy proce-
dure declared in the Core class record.
+o Calls XDestroyWindow if the widget is realized (that
is, has an X window). The server recursively
destroys all descendant windows.
+o Recursively descends the tree and deallocates all
pop-up widgets, constraint records, callback lists
and, if the widget is a subclass of
compositeWidgetClass, children.
SEE ALSO
XtAppCreateShell(3Xt) XtCreatePopupShell(3Xt)
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface