swift – 无法将Nil分配给AVCaptureDeviceInput类型

概述我试过注释掉deviceInput = nil这个行只是为了测试但是有其他错误.此代码存在于其他在线示例中,因此我不确定这里发生了什么. private func captureSetup (position : AVCaptureDevicePosition) { var captureError : NSError? var captureDevice : AVCaptureD 我试过注释掉deviceinput = nil这个行只是为了测试但是有其他错误.此代码存在于其他在线示例中,因此我不确定这里发生了什么.

private func capturesetup (position : AVCaptureDeviceposition) {    var captureError : NSError?    var captureDevice : AVCaptureDevice!    for testedDevice in AVCaptureDevice.devicesWithMediaType(AVMediaTypeVIDeo){        if (testedDevice.position == position) {            captureDevice = testedDevice as! AVCaptureDevice        }    }    if (captureDevice == nil) {        captureDevice = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVIDeo)    }    var deviceinput : AVCaptureDeviceinput    do {        deviceinput = try AVCaptureDeviceinput(device: captureDevice)    } catch let error as NSError {        captureError = error        deviceinput = nil  // Nil cannot be assigned to type AVCaptureDeviceinput        if captureError != nil { // new if            print("error: \(captureError?.localizedDescription)")        }    }    captureSession.sessionPreset = AVCaptureSessionPresetHigh    if (captureError == nil) {        if (captureSession.canAddinput(deviceinput)) {            captureSession.addinput(deviceinput)        }        self.vIDeoDataOutput = AVCaptureVIDeoDataOutput()        self.vIDeoDataOutput!.vIDeoSettings = [kCVPixelBufferPixelFormatTypeKey: Int(kCVPixelFormatType_32BGRA)]        self.vIDeoDataOutput!.alwaysdiscardsLateVIDeoFrames = true        self.vIDeoDataOutputQueue = dispatch_queue_create("VIDeoDataOutputQueue",disPATCH_QUEUE_SERIAL)        self.vIDeoDataOutput!.setSampleBufferDelegate(self,queue: self.vIDeoDataOutputQueue!)        if (captureSession.canAddOutput(self.vIDeoDataOutput)) {            captureSession.addOutput(self.vIDeoDataOutput)        }    }    visageCameraview.frame = UIScreen.mainScreen().bounds    let prevIEwLayer: AVCaptureVIDeoPrevIEwLayer = AVCaptureVIDeoPrevIEwLayer(session: captureSession) as AVCaptureVIDeoPrevIEwLayer // changed to let    prevIEwLayer.frame = UIScreen.mainScreen().bounds    prevIEwLayer.vIDeoGravity = AVLayerVIDeoGravityResizeAspectFill    visageCameraview.layer.addSublayer(prevIEwLayer)}

解决方法 这对我来说很有意义.如果你想把它设置为零.使用选项.这样你就可以把它设置为零.这是一个很好的机制来避免崩溃和大量的if语句进行空检查.我推荐的(即使是测试)是使用选项.这就是你的样子：

var deviceinput : AVCaptureDeviceinput?

现在,deviceinput不必保存任何有效值.所以你可以写下面的内容(虽然默认为nil)

deviceinput = nil

现在,假设您想在其他地方使用它.你可以使用如果像这样：

if let myNonNilValue = deviceinput {    // myNonNilValue is for sure not nil}

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