• (instancetype)initWithPresentedViewController:(UIViewController *)presentedViewController presentingViewController:(nullable UIViewController *)presentingViewController

UIViewController *controller = [[UIViewController alloc] init];
UIPopoverPresentationController *popController = [controller popoverPresentationController];
// 出现在UIBarButtonItem上面的
popController.delegate = self;
popController.barButtonItem = self.barItem;

// 出现在view上面的
UIPopoverPresentationController *popController = [controller popoverPresentationController];
popController.sourceView = self.button;
popController.sourceRect = self.button.bounds;
popController.delegate = self;
[self presentViewController:controller animated:YES completion:nil];