ios - init() 在 Swift 4 的 AVCaptureDeviceInput 中不可用

Question

我的应用程序中有一个像 Snapchat 一样显示后置摄像头的 View Controller ，它在 Swift 3 中运行良好，但是当我更新到 Swift 4 时，编译器不允许我运行它，因为出现以下错误:

init() is unavailable for AVCaptureDeviceInput

这个 View Controller 应该像 Snapchat 一样显示没有任何按钮或额外东西的相机。所以，这里是完整的 View Controller 代码:

import UIKit
import AVFoundation

class cameraViewController: UIViewController , UIImagePickerControllerDelegate , UINavigationControllerDelegate {

var captureSession : AVCaptureSession?

var stillImageOutput : AVCaptureStillImageOutput?

var previewLayer : AVCaptureVideoPreviewLayer?

var imagePicker: UIImagePickerController!

@IBOutlet weak var cameraView: UIView!

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

    previewLayer?.frame = cameraView.bounds
}

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)


    captureSession = AVCaptureSession()

    captureSession?.sessionPreset = AVCaptureSessionPreset1280x720

    let backCamera = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)

    let error : NSError?

    var input = AVCaptureDeviceInput()

    do {
        input = try AVCaptureDeviceInput(device: backCamera)
    }
    catch {
        //  error
    }

    if error == nil && (captureSession?.canAddInput(input))! {

        captureSession?.addInput(input)

        stillImageOutput = AVCaptureStillImageOutput()

        stillImageOutput?.outputSettings = [AVVideoCodecKey : AVVideoCodecJPEG]


        if (captureSession?.canAddOutput(stillImageOutput))! {

            captureSession?.addOutput(stillImageOutput)

            previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)

            previewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill

            previewLayer?.connection.videoOrientation = AVCaptureVideoOrientation.portrait

            cameraView.layer.addSublayer(previewLayer!)

            captureSession?.startRunning() 

        }
    }

}

}

由于这一行，我无法运行该应用程序:

var input = AVCaptureDeviceInput()

Answer 1

在 Swift 4 中，您必须指定一个设备才能初始化 AVCaptureDeviceInput - 事实上，您已经在初始化它，在抛出的代码之后用一两行错误。

此外，您在之后的 if 语句中隐式解包了一个安全解包的 AVCaptureSession。

这是你的代码，经过优化:

do {
    guard let input = try AVCaptureDeviceInput(device: backCamera),
        captureSession = captureSession else {
        print("Error in initializing a device input")
    }

    if error == nil && (captureSession.canAddInput(input)) {

    [...]
}
catch let error {
    print(error.localizedDescription)
}