The CupertinoTabBar.currentIndex is only used to initialize a CupertinoTabController when no controller is provided. Subsequently providing a different CupertinoTabBar.currentIndex does not affect the scaffold or the tab bar's active tab index. To programmatically change the active tab index, use a CupertinoTabController.
If CupertinoTabBar.onTap is provided, it will still be called.
CupertinoTabScaffold automatically also listen to the
onTap to change the controller's
and change the actively displayed tab in CupertinoTabScaffold's own
main content area.
If translucent, the main content may slide behind it. Otherwise, the main content's bottom margin will be offset by its height.
final CupertinoTabBar tabBar;