没有打印错误，但是函数没有运行

Question

我正在尝试显示相机视图，正如您在下面的代码中看到的那样，我将其设置为显示任何错误并且在出现任何错误时不会中断程序，但是当我这样做时运行此代码没有错误发生或显示相机视图。我运行在实际的 phone 上安装它，phone 确实请求它是否有权使用相机。下面是代码

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

    captureSession = AVCaptureSession()
    captureSession?.sessionPreset = AVCaptureSessionPreset1920x1080

    let backCamera = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
    var input : AVCaptureDeviceInput?
    let error : NSError?
    do {
        input = try AVCaptureDeviceInput(device: backCamera)
    } catch let error as NSError? {
        print(error)



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

            videoOutput = AVCaptureVideoDataOutput()
            //videoOutput?.outputSettings = [AVVideoCodecKey : AVVideoCodecKey]

                if ((captureSession?.canAddOutput(videoOutput)) != nil){
                    captureSession?.addOutput(videoOutput)

                    previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
                    previewLayer?.videoGravity = AVLayerVideoGravityResizeAspect
                    previewLayer?.connection.videoOrientation = AVCaptureVideoOrientation.Portrait
                    cameraView.layer.addSublayer(previewLayer!)
                    captureSession?.startRunning()
            }
        }
    }

}

Answer 1

不要将代码放在 catch 中。那就是万一出了问题。

do {
    input = try AVCaptureDeviceInput(device: backCamera)
} catch let error as NSError? {
    print(error)
    return//Stop rest of code
}
if (captureSession?.canAddInput(input))!{
        captureSession?.addInput(input)

        videoOutput = AVCaptureVideoDataOutput()
        //videoOutput?.outputSettings = [AVVideoCodecKey : AVVideoCodecKey]

            if ((captureSession?.canAddOutput(videoOutput)) != nil){
                captureSession?.addOutput(videoOutput)

                previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
                previewLayer?.videoGravity = AVLayerVideoGravityResizeAspect
                previewLayer?.connection.videoOrientation = AVCaptureVideoOrientation.Portrait
                cameraView.layer.addSublayer(previewLayer!)
                captureSession?.startRunning()
        }
    }

Answer 2

只有在发生错误时才会执行catch 的主体。因此，由于您的代码位于 catch 块内，因此它不会执行，因为它没有发现任何错误。因此，按照@penatheboss 的建议，从 catch 块中删除代码并将其放在外面。

没有打印错误，但是函数没有运行

No error printed however function doesn't run

ios

swift

swift2

avfoundation

avcapturesession

没有打印错误，但是函数没有 运行

No error printed however function doesn't run

ios

swift

swift2

avfoundation

avcapturesession

没有打印错误，但是函数没有运行