iPhone相机，如何避免预览视图上的cameraOverlay；如何知道何时进入预览视图

如何避免预览视图上的cameraOverlay

swift
import AVFoundation
import UIKit
class CameraViewController: UIViewController {
    var previewView: UIView!
    var captureSession: AVCaptureSession!
    var videoPreviewLayer: AVCaptureVideoPreviewLayer!
    override func viewDidLoad() {
        super.viewDidLoad()
        // 创建预览视图
        previewView = UIView(frame: view.bounds)
        view.addSubview(previewView)
        // 初始化摄像头
        captureSession = AVCaptureSession()
        guard let videoDevice = AVCaptureDevice.default(for: .video),
            let videoInput = try? AVCaptureDeviceInput(device: videoDevice),
            captureSession.canAddInput(videoInput) else { return }
        captureSession.addInput(videoInput)
        // 创建预览图层
        videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        videoPreviewLayer.videoGravity = .resizeAspectFill
        videoPreviewLayer.frame = previewView.bounds
        previewView.layer.addSublayer(videoPreviewLayer)
        // 启动摄像头
        captureSession.startRunning()
    }
}

swift
class CameraViewController: UIViewController {
    var captureSession: AVCaptureSession!
    override func viewDidLoad() {
        super.viewDidLoad()
        captureSession = AVCaptureSession()
        // 监听捕捉会话的running属性
        captureSession.addObserver(self, forKeyPath: "running", options: .new, context: nil)
    }
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if keyPath == "running", let isRunning = change?[.newKey] as? Bool {
            if isRunning {
                // 进入预览视图，执行一些操作
                print("进入预览视图")
            } else {
                // 离开预览视图，执行一些操作
                print("离开预览视图")
            }
        }
    }
}