XtCreateWidget(3)
NAME
XtCreateWidget, XtVaCreateWidget, XtCreateManagedWidget, XtVaCreateManagedWidget, XtDestroyWidget - create and destroy 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 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.
... 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.
· 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.
· 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, children.
SEE ALSO
XtAppCreateShell(3), XtCreatePopupShell(3) X Toolkit Intrinsics - C Language Interface Xlib - C Language X Interface
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