XtCreateWidget(3Xt) XT FUNCTIONS XtCreateWidget(3Xt)
NAME
XtCreateWidget, XtVaCreateWidget, XtCreateManagedWidget,
XtVaCreateManagedWidget, XtDestroyWidget - create and des-
troy widgets
SYNTAX
Widget XtCreateWidget(String name, WidgetClass widget_class,
Widget parent, ArgList args, Cardinal num_args);
Widget XtVaCreateWidget(String name, WidgetClass
widget_class, Widget parent, ...);
Widget XtCreateManagedWidget(String name, WidgetClass
widget_class, Widget parent, ArgList args, Cardinal
num_args);
Widget XtVaCreateManagedWidget(String name, WidgetClass
widget_class, Widget parent, ...);
void XtDestroyWidget(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 argument
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 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) XT FUNCTIONS 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 exam-
ple, 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 con-
straintWidgetClass.
+ 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 cal-
ling 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 con-
straint 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) XT FUNCTIONS 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 descen-
dent 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 composi-
teWidgetClass 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 Sec-
tion 3.4).
+ If the widget's parent is a subclass of con-
straintWidgetClass, 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 des-
cendants) 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) XT FUNCTIONS XtCreateWidget(3Xt)
children.
SEE ALSO
XtAppCreateShell(3Xt), XtCreatePopupShell(3Xt)
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface
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