present 一个透明的viewController

PieChartViewController *pieChartVC = [[PieChartViewControlleralloc] init];

        pieChartVC.modalTransitionStyle =UIModalTransitionStyleFlipHorizontal;;

        

        //根视图操作，实现present一个透明Controller

//注意要在根视图上进行操作

//modalPresentationStyle 设置为 UIModalPresentationCurrentContext

        UIViewController* controller =self.view.window.rootViewController;

        controller.modalPresentationStyle =UIModalPresentationCurrentContext;

        [controller presentViewController:pieChartVCanimated:YEScompletion:nil];