XtAddGrab

Section: XT FUNCTIONS (3)
Updated: libXt 1.1.5
Index Return to Main Contents

NAME

XtAddGrab, XtRemoveGrab - redirect user input to a modal widget

SYNTAX

: void XtAddGrab(Widget w, Boolean exclusive, Boolean spring_loaded);
: void XtRemoveGrab(Widget w);

ARGUMENTS

exclusive: Specifies whether user events should be dispatched exclusively to this widget or also to previous widgets in the cascade.
spring_loaded: Specifies whether this widget was popped up because the user pressed a pointer button.
w: Specifies the widget to add to or remove from the modal cascade.

DESCRIPTION

The XtAddGrab function appends the widget (and associated parameters) to the modal cascade and checks that exclusive is True if spring_loaded is True. If these are not True, XtAddGrab generates an error.

The modal cascade is used by XtDispatchEvent when it tries to dispatch a user event. When at least one modal widget is in the widget cascade, XtDispatchEvent first determines if the event should be delivered. It starts at the most recent cascade entry and follows the cascade up to and including the most recent cascade entry added with the exclusive parameter True.

This subset of the modal cascade along with all descendants of these widgets comprise the active subset. User events that occur outside the widgets in this subset are ignored or remapped. Modal menus with submenus generally add a submenu widget to the cascade with exclusive False. Modal dialog boxes that need to restrict user input to the most deeply nested dialog box add a subdialog widget to the cascade with exclusive True. User events that occur within the active subset are delivered to the appropriate widget, which is usually a child or further descendant of the modal widget.

Regardless of where on the screen they occur, remap events are always delivered to the most recent widget in the active subset of the cascade that has spring_loaded True, if any such widget exists.

The XtRemoveGrab function removes widgets from the modal cascade starting at the most recent widget up to and including the specified widget. It issues an error if the specified widget is not on the modal cascade.