AVCamViewController没有可见的@interface声明选择器层

当我尝试使用videogravity代码时，它显示了错误，

No visible@interface for AVCamViewController

声明了选择器层，当它在AVCAM示例中表示“self layer”时，它在三条底线上声明了选择器层？我该如何解决这个问题

- (void)setSession:(AVCaptureSession *)session {
    ((AVPlayerLayer *)[self layer]).videoGravity = AVLayerVideoGravityResizeAspectFill;
    ((AVPlayerLayer *)[self layer]).bounds = ((AVPlayerLayer *)[self layer]).bounds;
    [(AVCaptureVideoPreviewLayer *)[self layer] setSession:session];
}