我试图取代第一层与相机预览层，但它不显示任何模拟器与白色屏幕出现。

(void) setUpGreyLayer {
         
         // TODO : This layer will be replaced with camera preview layer
         self.firstLayer = [CALayer layer];
         self.firstLayer.frame = [UIScreen mainScreen].bounds;
         self.firstLayer.backgroundColor = [UIColor whiteColor].CGColor;
     
         //Adding the greyLayer on top of firstLayer
         self.greyLayer = [CALayer layer];
         self.greyLayer.frame = self.firstLayer.bounds;
         self.greyLayer.backgroundColor = [UIColor grayColor].CGColor;
         self.greyLayer.opacity = 0.5;
           
         // Create a mask layer with a clear rounded rectangle shape in the center
         self.maskLayer = [CAShapeLayer layer];
         CGRect maskRect = CGRectMake((CGRectGetWidth(self.greyLayer.bounds) - 200) / 2.0, (CGRectGetHeight(self.greyLayer.bounds) - 250) / 2.0 - 0.10 * CGRectGetHeight(self.greyLayer.bounds), 200, 250);
         CGFloat cornerRadius = 77.0;
         UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:maskRect cornerRadius:cornerRadius];
         [maskPath appendPath:[UIBezierPath bezierPathWithRect:self.greyLayer.bounds].bezierPathByReversingPath];
         self.maskLayer.path = maskPath.CGPath;
     
         // Set the mask layer to the greyLayer
         self.greyLayer.mask = self.maskLayer;
         [self.view.layer addSublayer:self.firstLayer];
         [self.view.layer addSublayer:self.greyLayer];
         [self setUpCaptureButton];
     }

现在我的下一个行动计划是用相机预览层替换第一层。但是当我添加相机预览层时，模拟器只显示一个没有覆盖的空白白色屏幕，并且捕获按钮是否有preview_layer的任何特定属性，应该将其标记为选中/未选中以使灰色覆盖出现在顶部。
我试图取代第一层与相机预览层，但它不显示任何模拟器与白色屏幕出现。
我试图取代第一层与相机预览层，但它不显示任何模拟器与白色屏幕出现。

- (void) viewDidLoad {
    [super viewDidLoad];
    
    [self setUpGreyLayer];
    
        [self setUpCaptureSession];
        [self setUpPreviewLayer];
        [self setUpCaptureButton];
  }

- (void)setUpPreviewLayer {
    self.previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:self.captureSession];
    self.previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    self.previewLayer.frame = self.view.bounds;
    [self.view.layer addSublayer:self.previewLayer];
}
(void) setUpGreyLayer {
         
         // TODO : This layer will be replaced with camera preview layer
         
>! self.firstLayer = [CALayer layer];
>! self.firstLayer.frame = [UIScreen mainScreen].bounds;
>! self.firstLayer.backgroundColor = [UIColor whiteColor].CGColor;
     
         //Adding the greyLayer on top of previewLayer
         self.greyLayer = [CALayer layer];
         self.greyLayer.frame = self.previewLayer.bounds;
         self.greyLayer.backgroundColor = [UIColor grayColor].CGColor;
         self.greyLayer.opacity = 0.5;
           
         // Create a mask layer with a clear rounded rectangle shape in the center
         self.maskLayer = [CAShapeLayer layer];
         CGRect maskRect = CGRectMake((CGRectGetWidth(self.greyLayer.bounds) - 200) / 2.0, (CGRectGetHeight(self.greyLayer.bounds) - 250) / 2.0 - 0.10 * CGRectGetHeight(self.greyLayer.bounds), 200, 250);
         CGFloat cornerRadius = 77.0;
         UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:maskRect cornerRadius:cornerRadius];
         [maskPath appendPath:[UIBezierPath bezierPathWithRect:self.greyLayer.bounds].bezierPathByReversingPath];
         self.maskLayer.path = maskPath.CGPath;
     
         // Set the mask layer to the greyLayer
         self.greyLayer.mask = self.maskLayer;
>! [self.view.layer addSublayer:self.firstLayer];
         [self.view.layer addSublayer:self.greyLayer];
         [self setUpCaptureButton];
     }