XtCreateWidget(3Xt) X Version 11 (Release 3) XtCreateWidget(3Xt)
NAME
XtCreateWidget, XtCreateManagedWidget, 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 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.
num_args Specifies the number of arguments in the argument
list.
parent Specifies the parent widget.
w Specifies the widget.
widget_class
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.
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XtCreateWidget(3Xt) X Version 11 (Release 3) XtCreateWidget(3Xt)
⊕ 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 superclasses.
⊕ 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.
⊕ 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 11.1.
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 immediately.
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XtCreateWidget(3Xt) X Version 11 (Release 3) XtCreateWidget(3Xt)
⊕ 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 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:
⊕ 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).
⊕ 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 window). The server recursively destroys
all descendant windows.
⊕ Recursively descends the tree and deallocates all pop-
up widgets, constraint records, callback lists and, if
the widget is a subclass of compositeWidgetClass,
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XtCreateWidget(3Xt) X Version 11 (Release 3) XtCreateWidget(3Xt)
children.
SEE ALSO
XtAppCreateShell(3Xt), XtCreatePopupShell(3Xt)
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface
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