去掉presentmodalviewcontroller背景色

for (UIView *view in registViewController.view.superview.subviews) {
        if ([view isKindOfClass:[UIImageView class]]) {
            [view removeFromSuperview];
        }

    }

或者

UIViewController * controller1 = [[UIViewController alloc] init];

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

controller.modalPresentationStyle = UIModalPresentationCurrentContext;

[controller presentModalViewController: controller1 animated:YES];