尝试启动前置摄像头时出现错误（Swift）

Question

I get an error when I try to use the following code:

   captureSession = AVCaptureSession()
    captureSession!.sessionPreset = AVCaptureSessionPresetPhoto

    //var backCamera = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)

    let videoDevices = AVCaptureDevice.devicesWithMediaType(AVMediaTypeVideo)
    var captureDevice:AVCaptureDevice

    for device in videoDevices{
        let device = device as AVCaptureDevice
        if device.position == AVCaptureDevicePosition.Front {
            captureDevice = device
            break
        }
    }


    var error: NSError?
    var input = AVCaptureDeviceInput(device: captureDevice, error: &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 = AVLayerVideoGravityResizeAspect
            previewLayer!.connection?.videoOrientation = AVCaptureVideoOrientation.Portrait
            previewView.layer.addSublayer(previewLayer)

            captureSession!.startRunning()
        }
    }

The line: var input = AVCaptureDeviceInput(device: captureDevice, error: &error) is giving me the error: Variable CaptureDevice used before being initialized . Can someone help me how to fix this?

Thank you so much!

Answer 1

This is because captureDevice may be used before being initialized:

var captureDevice:AVCaptureDevice

for device in videoDevices{
    let device = device as AVCaptureDevice
    if device.position == AVCaptureDevicePosition.Front {
        captureDevice = device
        break
    }
}

If the loop doesn't find a front camera, captureDevice will be used before being initialized. To work around this, declare captureDevice as an implicitly unwrapped optional, and initialize it to nil :

var captureDevice:AVCaptureDevice! = nil