AVCaptureSession崩溃了

Question

我用这个代码来拍照片，我不能尽快拍到照片。快速拍摄多张照片，应用程序就会崩溃。

我用的是Swift 1.1。

错误：

由于异常“NSInvalidArgumentException”终止应用程序，原因：‘+AVCaptureStillImageOutput：- NULL示例缓冲区。’。

 class ViewController: UIViewController {
    let captureSession = AVCaptureSession()
    var previewLayer : AVCaptureVideoPreviewLayer?
    var captureDevice : AVCaptureDevice?
    var captureConnection: AVCaptureConnection?
    var stillImageOutput = AVCaptureStillImageOutput()
    let targetRegion = CALayer()
    var currentImage: UIImage?

    @IBOutlet weak var cameraView: UIImageView!
    @IBOutlet weak var imageDisplayed: UIImageView!


    override func viewDidLoad() {
        super.viewDidLoad()

        navigationController?.setNavigationBarHidden(true, animated: true)

        captureSession.sessionPreset = AVCaptureSessionPreset1920x1080
        let devices = AVCaptureDevice.devices()
        for device in devices {
            if device.hasMediaType(AVMediaTypeVideo) {
                if device.position == AVCaptureDevicePosition.Back {
                    captureDevice = device as? AVCaptureDevice
                }
            }
        }
        if captureDevice != nil {
            println("Device trovato")
            beginSession()
        }


    }


    func beginSession() {

        var err: NSError? = nil
        captureSession.addInput(AVCaptureDeviceInput(device: captureDevice, error: &err))

        if err != nil {
            println("err \(err?.localizedDescription)")
            return
        }

        previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        self.view.layer.addSublayer(previewLayer)

        previewLayer?.frame = CGRect(x: cameraView.frame.origin.x, y: cameraView.frame.origin.y, width: cameraView.frame.size.width, height: cameraView.frame.size.height)

        captureSetup()
        captureSession.startRunning()
    }

    func captureSetup() {

        let outputSetting = NSDictionary(dictionary: [AVVideoCodecKey: AVVideoCodecJPEG])
        self.stillImageOutput.outputSettings = outputSetting
        self.captureSession.addOutput(stillImageOutput)
        for connection:AVCaptureConnection in self.stillImageOutput.connections as [AVCaptureConnection] {

            for port:AVCaptureInputPort in connection.inputPorts! as [AVCaptureInputPort] {
                if port.mediaType == AVMediaTypeVideo {
                    captureConnection = connection as AVCaptureConnection
                    break
                }
            }
            if captureConnection != nil {
                break
            }
        }
    }


    var i = 0;

    func captureScene() {


        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
            if self.captureConnection != nil {
                self.stillImageOutput.captureStillImageAsynchronouslyFromConnection(self.captureConnection, completionHandler:{ (imageSampleBuffer:CMSampleBuffer!, _) -> Void in

                    let imageDataJpeg = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(imageSampleBuffer)
                    var pickedImage: UIImage = UIImage(data:imageDataJpeg)!



                    if let data = UIImagePNGRepresentation(pickedImage) {


                        let filename = self.getDocumentsDirectory().stringByAppendingPathComponent("\(self.i).png")
                        data.writeToFile(filename, atomically: true)

                        self.i++
                    }


                })
            }
        })

    }



    func getDocumentsDirectory() -> NSString {
        let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
        let documentsDirectory: AnyObject = paths[0]


        return documentsDirectory as NSString
    }




    override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
        captureScene()
    }

}

Answer 1

@alper在linked answer中解释的是，有时imageSampleBuffer可以是零，这就是崩溃的根源。

我相信在Swift 2中imageSampleBuffer是一个可选的，所以为了避免这种崩溃，您可以检查为零。示例：

if imageSampleBuffer != nil {
    let imageDataJpeg = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(imageSampleBuffer)
    // ...
} else {
    // handle or ignore the error
}

但是您使用的是Swift 1，这是一个问题，因为在Swift 1中，imageSampleBuffer被声明为一个隐式未包装的可选选项，这意味着它不能是零，并且不能像前面的示例那样检查。

@alper给出的解决方案是使用

CMSampleBufferIsValid(imageSampleBuffer)

作为检查缓冲区是否有效的方法。

如果前面的解决方案不起作用，您可以尝试这样做。

当我查看函数签名时：

self.stillImageOutput.captureStillImageAsynchronouslyFromConnection(self.captureConnection, completionHandler:{ (imageSampleBuffer:CMSampleBuffer!, _) -> Void in

我看到缓冲区旁边有另一个参数，但是您忽略了它：

(imageSampleBuffer:CMSampleBuffer!，_)

我没有查找Swift 1文档，但是如果_实际上是一个错误参数，我不会感到惊讶。尝试用error替换它，如下所示：

self.stillImageOutput.captureStillImageAsynchronouslyFromConnection(self.captureConnection, completionHandler:{ (imageSampleBuffer:CMSampleBuffer!, error) -> Void in

或者也许

self.stillImageOutput.captureStillImageAsynchronouslyFromConnection(self.captureConnection, completionHandler:{ (imageSampleBuffer:CMSampleBuffer!, error:NSError) -> Void in

然后在继续使用error之前检查imageSampleBuffer的内容。

注意:正如我最后说过的，使用error__的解决方案是猜测，我没有测试:您必须尝试，调整，看看我的想法是否正确。如果您能够找到Swift 1的文档，并明确地告诉我们有关它的情况，那将是非常理想的。