tabBarController点击bar 传值

//没有导航
OrderViewController *orderVC = [self.tabBarController.viewControllers objectAtIndex:2];

//有导航的
UINavigationController *temp = (UINavigationController *)[super.tabBarController.viewControllers objectAtIndex:2];
OrderViewController *orderVC = (OrderViewController *)temp.topViewController;
orderVC.currentIndex = 1;//选中待付款按钮
 self.tabBarController.selectedIndex = 2;//跳转