Synchronizes the pop-up button’s displayed item with the currently selected menu item.
- macOS 10.0+
If no item is currently selected, this method synchronizes the pop-up buttons displayed item with the first menu item. If the pop-up button cell does not get its displayed item from a menu item, this method does nothing.
For pull-down menus, this method sets the displayed item to the title first menu item.
If the pop-up button’s menu does not contain any menu items, this method sets the pop-up button’s displayed item to
nil, resulting in nothing being displayed in the control.