XtCreateWidget(Xt) X Version 11 (Release 5) XtCreateWidget(Xt)
6 January 1993
Name
XtCreateWidget - 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 XtCreateManagedWidget(name, widget_class, parent, args, num_args)
String name;
WidgetClass widget_class;
Widget parent;
ArgList args;
Cardinal num_args;
void XtDestroyWidget(w)
Widget w;
Arguments
args Specifies the argument list to override the resource defaults.
name Specifies the resource name for the created widget, 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.
numargs Specifies the number of arguments in the argument list.
parent Specifies the parent widget.
w Specifies the widget.
widgetclass
Specifies the widget class pointer for the created widget.
Description
The XtCreateWidget function performs much of the boilerplate operations
of widget creation:
+ 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.
+ Allocates memory for the widget instance.
+ 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 constraints field.
+ Initializes the core nonresource data fields (for example, parent and
visible).
+ Initializes the resource fields (for example, background_pixel) by
using the resource lists specified for this class and all superc-
lasses.
+ If the parent is a subclass of constraintWidgetClass, it initializes
the resource fields of the constraints record by using the constraint
resource list specified for the parent's class and all superclasses up
to constraintWidgetClass.
+ Calls the initialize procedures for the widget by starting at the Core
initialize procedure on down to the widget's initialize procedure.
+ 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 of X
Toolkit Intrinsics - C Language Interface.
+ If the parent is a subclass of constraintWidgetClass, it calls the
constraint initialize procedures, starting 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 11.2
of X Toolkit Intrinsics - C Language Interface.
The XtCreateManagedWidget function is a convenience routine 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, including from an application callback routine of the
widget being destroyed. This requires a two-phase destroy process in
order to avoid dangling references to destroyed widgets.
In phase one, XtDestroyWidget performs the following:
+ If the being_destroyed field of the widget is True, it returns immedi-
ately.
+ Recursively descends the widget tree and sets the being_destroyed
field to True for the widget and all children.
+ 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 (including all procedures registered
with the event and translation managers), that is, when the current invo-
cation 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:
+ Calls the destroy callback procedures registered on the widget (and
all descendants) in post-order (it calls children callbacks before
parent callbacks).
+ If the widget's parent is a subclass of compositeWidgetClass 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 of X Toolkit Intrinsics - C Language Interface).
+ 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.
+ 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 procedure declared
in the Core class record.
+ Calls XDestroyWindow if the widget is realized (that is, has an X win-
dow). The server recursively destroys all descendant windows.
+ Recursively descends the tree and deallocates all pop-up widgets, con-
straint records, callback lists and, if the widget is a subclass of
compositeWidgetClass, children.
See also
XtAppCreateShell(Xt) and XtCreatePopupShell(Xt).
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface