Question

我想观察火炬的状态并设置按钮的tintColor，但不会调用observeValue。我做错了什么？

ViewController.swift

import UIKit
import AVFoundation

class ViewController: UIViewController {

    @IBOutlet weak var previewView: PreviewView!
    private let session = AVCaptureSession()
    private var videoDevice: AVCaptureDevice!
    private var observeContext = 0;

    override func viewDidLoad() {
        super.viewDidLoad()
        // Assume access is granted
        previewView.session = session
        sessionQueue.async { [unowned self] in
            self.configureSession()
        }
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        sessionQueue.async { [unowned self] in
            self.session.startRunning();
        }
    }

    override func viewWillDisappear(_ animated: Bool) {
        sessionQueue.async { [unowned self] in
            if self.session.isRunning {
                self.session.stopRunning()
            }
            if let device = self.videoDevice {
                device.removeObserver(self, forKeyPath: #keyPath(AVCaptureDevice.isTorchActive))
            }
        }
        super.viewWillDisappear(animated)
    }

    private func configureSession() {  
        session.beginConfiguration()
        do {
            if let backCameraDevice = AVCaptureDevice.defaultDevice(withDeviceType: .builtInWideAngleCamera, mediaType: AVMediaTypeVideo, position: .back) {
                self.videoDevice = backCameraDevice

                backCameraDevice.addObserver(self, forKeyPath: #keyPath(AVCaptureDevice.isTorchActive), options: [.new], context: &observeContext)

                let videoDeviceInput = try AVCaptureDeviceInput(device: backCameraDevice)
                if session.canAddInput(videoDeviceInput) {
                    session.addInput(videoDeviceInput)
                }
            }
        }
        catch {
            print("Could not create video device input: \(error)")
        }
        session.commitConfiguration()
    }

    @IBAction func btnClick(_ sender: Any) {
        sessionQueue.async { [unowned self] in
            if let device = self.videoDevice, device.isTorchAvailable {
                do {
                    try device.lockForConfiguration()
                    if device.isTorchActive {
                        device.torchMode = .off
                    } else {
                        device.torchMode = .on
                    }
                    device.unlockForConfiguration()
                } catch {
                    print("Could not configure torch: \(error)")
                }
            }
        }
    }

    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        let newValue = change?[.newKey]

        if context == &observeContext {
            print(newValue)
        } else {
            super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
        }
    }
}

Answer 1

使用#keyPath(AVCaptureDevice.torchActive) - 请注意缺少is。您必须通过Objective-C名称观察属性，而不是通过“重命名”Swift 3名称。

如何观察AVCaptureDevice.isTorchActive

1 个答案: