ios - 当我尝试启动前置摄像头时出现错误 (Swift)

Question

当我尝试使用以下代码时出现错误:

   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()
        }
    }

行:var input = AVCaptureDeviceInput(device: captureDevice, error: &error) 给我错误:Variable CaptureDevice used before being initialized。有人可以帮我解决这个问题吗？

非常感谢!

Answer 1

这是因为 captureDevice 可能在初始化之前被使用:

var captureDevice:AVCaptureDevice

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

如果循环没有找到前置摄像头，captureDevice 将在初始化之前使用。要解决此问题，请将 captureDevice 声明为隐式解包可选，并将其初始化为 nil:

var captureDevice:AVCaptureDevice! = nil