在Swift中使用按钮切换相机

func switchCamera(_ sender: UIButton) {
    if let session = AVCaptureSession() {
        let currentCameraInput: AVCaptureInput = session.inputs[0]
        session.removeInput(currentCameraInput)
        var newCamera: AVCaptureDevice
        newCamera = AVCaptureDevice.default(for: AVMediaType.video)!

            if (currentCameraInput as! AVCaptureDeviceInput).device.position == .BACk {
                UIView.transition(with: self.cameraView,duration: 0.5,options: .transitionFlipFromLeft,animations: {
                    newCamera = self.cameraWithPosition(.front)!
                },completion: nil)
            } else {
                UIView.transition(with: self.cameraView,options: .transitionFlipFromRight,animations: {
                    newCamera = self.cameraWithPosition(.BACk)!
                },completion: nil)
            }
            do {
                try self.captureSession?.addInput(AVCaptureDeviceInput(device: newCamera))
            }
            catch {
                print("error: \(error.localizedDescription)")
            }

    }
}

func cameraWithPosition(_ position: AVCaptureDevice.Position) -> AVCaptureDevice? {
    let deviceDescoverySession = AVCaptureDevice.DiscoverySession.init(deviCETypes: [AVCaptureDevice.DeviCEType.builTinWideAngleCamera],mediaType: AVMediaType.video,position: AVCaptureDevice.Position.unspecified)

    for device in deviceDescoverySession.devices {
        if Device.position == position {
            return device
        }
    }
    return nil
}