e815. 监听当前选择的的菜单或菜单项

The currently selected menu or menu item in a JMenu or JPopupMenu is tracked by MenuSelectionManager. To receive notification of changes to the currently selected menu or menu item, a change listener must be registered with the MenuSelectionManager.

    // Create a change listener and register with the menu selection manager
    MenuSelectionManager.defaultManager().addChangeListener(
        new ChangeListener() {
            public void stateChanged(ChangeEvent evt) {
                // Get the selected menu or menu item
                MenuSelectionManager msm = (MenuSelectionManager)evt.getSource();
                MenuElement[] path = msm.getSelectedPath();
                // To interpret path, see
                // e813 获得当前选择的菜单或菜单项

                if (path.length == 0) {
                    // All menus are hidden
                }
            }
        }
    );

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