Cocoa touch UIModalPresentationFormSheet白色角

我尝试使用背景为深色的UIModalPresentationFormSheet，但视图的各个角落总是有一点白色显示

你可以看到一幅画

我以前从未见过这种情况。您知道是什么导致了这种情况吗？

首先导入“QuartzCore/QuartzCore.h”，其中ViewController将显示为UIModalPresentationFormSheet，然后覆盖视图

- (void)viewWillAppear:(BOOL)animated 
{
    [super viewWillAppear:animated];
    self.view.superview.layer.cornerRadius = 10;
    self.view.superview.layer.borderColor = [UIColor darkGrayColor].CGColor;
    self.view.superview.layer.borderWidth = 1;
    self.view.superview.clipsToBounds = YES;
}

---

如果需要阴影，则不应剪裁到superview的边界

此解决方案将使阴影保持可见

self.view.superview.layer.cornerRadius = 7.f;
for (CALayer *layer in self.view.superview.layer.sublayers)
    if (layer != self.view.layer)
        layer.cornerRadius = 8.f;

specpoover*ctrl=[[specpoover alloc]initWithNibName:@“specpoover”bundle:nil]；
//创建导航控制器
UINavigationController*导航控制器=[[UINavigationController alloc]
initWithRootViewController:ctrl]；
[self.navigationController-pushViewController:ctrl-animated:YES]；
navController.modalPresentationStyle=UIModalPresentationFormSheet；
navController.modalTransitionStyle=UIModalTransitionStyleCross溶解；
navController.view.backgroundColor=[UIColor clearColor]；
//以模式显示导航控制器
[自我呈现ModalViewController:navController动画：是]；
navController.view.superview.frame=CGRectMake（200400400）；
//以下操作将删除拐角处的白色圆边。欢迎来到堆栈溢出！请解释你的代码片段是如何工作的，以及它是如何解决问题的。有人能解释一下发生了什么事吗？？？@Kunal，重新绘制角半径请参见我在这个相关问题中的答案：
    SpecPopover *ctrl = [[SpecPopover alloc] initWithNibName:@"SpecPopover" bundle:nil];

     // Create a Navigation controller
     UINavigationController *navController = [[UINavigationController alloc]
                                                         initWithRootViewController:ctrl];

     [self.navigationController pushViewController:ctrl animated:YES];
     navController.modalPresentationStyle = UIModalPresentationFormSheet;
     navController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
     navController.view.backgroundColor = [UIColor clearColor];        

     // show the navigation controller modally
     [self presentModalViewController:navController animated:YES];
      navController.view.superview.frame = CGRectMake (200,200,400,400);
     // Following removes the white round edges from the corner.       <<<<<<<<-------------   
     navController.view.superview.layer.cornerRadius = 8;
     navController.view.superview.layer.borderColor = [UIColor clearColor].CGColor;
     navController.view.superview.layer.borderWidth = 2;
     navController.view.superview.clipsToBounds = YES;
 [navController release];
        [ctrl release];