Cannot get camera image - ios

Question

I created a simple app supposes to show a live image to a view from iPhone camera modifying this tutorial which is written in Swift2 into Swift3.
I use Xcode 8.1 and run the app on iPhone 6 with iOS version of 9.3.4
my Xcode deployment target setting is 9.1
When I run the app, the code complete without an error but camera image is not showing. The app doesn't even show permission alert for using camera.
What am I doing wrong?
Following is my complete code.
import UIKit
import AVFoundation
class ViewController: UIViewController {
// MARK: UI
let cameraView: UIView = {
let v = UIView()
v.translatesAutoresizingMaskIntoConstraints = false
return v
}()
// MARK: System
var captureSession = AVCaptureSession()
var sessionOutput = AVCaptureStillImageOutput()
var previewLayer = AVCaptureVideoPreviewLayer()
override func viewDidLoad() {
super.viewDidLoad()
setupSubviews()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
cameraSetup()
}
func setupSubviews() {
view.addSubview( cameraView )
cameraView.backgroundColor = UIColor.orange
cameraView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
cameraView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
cameraView.widthAnchor.constraint(equalToConstant: 200).isActive = true
cameraView.heightAnchor.constraint(equalToConstant: 200).isActive = true
}
func cameraSetup() {
print("**** Start Camera Setup ****")
let devices = AVCaptureDevice.devices(withMediaType: AVMediaTypeVideo)! as! [AVCaptureDevice]
for device in devices {
if device.position == .front {
print("Front")
do {
let input = try AVCaptureDeviceInput(device: device)
if captureSession.canAddInput(input) {
captureSession.addInput(input)
sessionOutput.outputSettings = [AVVideoCodecKey: AVVideoCodecJPEG]
print("Input added")
if captureSession.canAddOutput(sessionOutput) {
captureSession.addOutput(sessionOutput)
captureSession.startRunning()
previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill
previewLayer.connection.videoOrientation = AVCaptureVideoOrientation.portrait
cameraView.layer.addSublayer(previewLayer)
previewLayer.position = CGPoint(x: self.cameraView.frame.width / 2, y: self.cameraView.frame.height / 2)
previewLayer.bounds = cameraView.frame
print("Output added")
}
}
} catch {
print("Error")
}
}
}
print("**** Finish Camera Setup ****")
}
}