This is the example of camera view for iOS written in Swift

CameraViewController.swift

import UIKit
import AVFoundation

class ViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {

    @IBOutlet weak var myView: UIView!
    
    var session: AVCaptureSession?
    var device: AVCaptureDevice?
    var input: AVCaptureDeviceInput?
    var output: AVCaptureMetadataOutput?
    var prevLayer: AVCaptureVideoPreviewLayer?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        createSession()
    }
    
    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        prevLayer?.frame.size = myView.frame.size
    }
    
    func createSession() {
        session = AVCaptureSession()
        device = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
        
        var error: NSError? = nil
        input = AVCaptureDeviceInput(device: device, error: &error)
        if error == nil {
            session?.addInput(input)
        } else {
            println("camera input error: \(error)")
        }
       
        prevLayer = AVCaptureVideoPreviewLayer(session: session)
        prevLayer?.frame.size = myView.frame.size
        prevLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
        
        prevLayer?.connection.videoOrientation = transformOrientation(UIInterfaceOrientation(rawValue: UIApplication.sharedApplication().statusBarOrientation.rawValue)!)
        
        myView.layer.addSublayer(prevLayer)
        
        session?.startRunning()
    }

    func cameraWithPosition(position: AVCaptureDevicePosition) -> AVCaptureDevice? {
        let devices = AVCaptureDevice.devicesWithMediaType(AVMediaTypeVideo)
        for device in devices {
            if device.position == position {
                return device as? AVCaptureDevice
            }
        }
        return nil
    }
    
    override func viewWillTransitionToSize(size: CGSize, withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator) {
        coordinator.animateAlongsideTransition({ (context) -> Void in
            self.prevLayer?.connection.videoOrientation = self.transformOrientation(UIInterfaceOrientation(rawValue: UIApplication.sharedApplication().statusBarOrientation.rawValue)!)
            self.prevLayer?.frame.size = self.myView.frame.size
            }, completion: { (context) -> Void in
                
        })
        super.viewWillTransitionToSize(size, withTransitionCoordinator: coordinator)
    }
    
    func transformOrientation(orientation: UIInterfaceOrientation) -> AVCaptureVideoOrientation {
        switch orientation {
        case .LandscapeLeft:
            return .LandscapeLeft
        case .LandscapeRight:
            return .LandscapeRight
        case .PortraitUpsideDown:
            return .PortraitUpsideDown
        default:
            return .Portrait
        }
    }
    
    @IBAction func switchCameraSide(sender: AnyObject) {
        if let sess = session {
            let currentCameraInput: AVCaptureInput = sess.inputs[0] as! AVCaptureInput
            sess.removeInput(currentCameraInput)
            var newCamera: AVCaptureDevice
            if (currentCameraInput as! AVCaptureDeviceInput).device.position == .Back {
                newCamera = self.cameraWithPosition(.Front)!
            } else {
                newCamera = self.cameraWithPosition(.Back)!
            }
            let newVideoInput = AVCaptureDeviceInput(device: newCamera, error: nil)
            session?.addInput(newVideoInput)
        }
    }

}

This is helpful, thanks!

Excellent. Thank you

This is an update with iOS 12 and Swift 4

import UIKit
import AVFoundation

class ViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    
    @IBOutlet weak var cameraView: UIView!
    
    var session: AVCaptureSession?
    var device: AVCaptureDevice?
    var input: AVCaptureDeviceInput?
    var output: AVCaptureMetadataOutput?
    var prevLayer: AVCaptureVideoPreviewLayer?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        createSession()
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        prevLayer?.frame.size = cameraView.frame.size
    }
    
    func createSession() {
        session = AVCaptureSession()
        device = AVCaptureDevice.default(for: AVMediaType.video)
        
        do{
            input = try AVCaptureDeviceInput(device: device!)
        }
        catch{
            print(error)
        }
        
        if let input = input{
            session?.addInput(input)
        }
        
        prevLayer = AVCaptureVideoPreviewLayer(session: session!)
        prevLayer?.frame.size = cameraView.frame.size
        prevLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill
        
        prevLayer?.connection?.videoOrientation = transformOrientation(orientation: UIInterfaceOrientation(rawValue: UIApplication.shared.statusBarOrientation.rawValue)!)
        
        cameraView.layer.addSublayer(prevLayer!)
        
        session?.startRunning()
    }
    
    func cameraWithPosition(position: AVCaptureDevice.Position) -> AVCaptureDevice? {
        let deviceDiscoverySession = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInDualCamera, .builtInTelephotoCamera, .builtInTrueDepthCamera, .builtInWideAngleCamera, ], mediaType: .video, position: position)
        
        if let device = deviceDiscoverySession.devices.first {
            return device
        }
        return nil
    }
    
    override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
        coordinator.animate(alongsideTransition: { (context) -> Void in
            self.prevLayer?.connection?.videoOrientation = self.transformOrientation(orientation: UIInterfaceOrientation(rawValue: UIApplication.shared.statusBarOrientation.rawValue)!)
            self.prevLayer?.frame.size = self.cameraView.frame.size
        }, completion: { (context) -> Void in
            
        })
        super.viewWillTransition(to: size, with: coordinator)
    }
    
    func transformOrientation(orientation: UIInterfaceOrientation) -> AVCaptureVideoOrientation {
        switch orientation {
        case .landscapeLeft:
            return .landscapeLeft
        case .landscapeRight:
            return .landscapeRight
        case .portraitUpsideDown:
            return .portraitUpsideDown
        default:
            return .portrait
        }
    }
    
    @IBAction func switchCameraSide(sender: AnyObject) {
        if let sess = session {
            let currentCameraInput: AVCaptureInput = sess.inputs[0]
            sess.removeInput(currentCameraInput)
            var newCamera: AVCaptureDevice
            if (currentCameraInput as! AVCaptureDeviceInput).device.position == .back {
                newCamera = self.cameraWithPosition(position: .front)!
            } else {
                newCamera = self.cameraWithPosition(position: .back)!
            }
            
            var newVideoInput: AVCaptureDeviceInput?
            do{
                newVideoInput = try AVCaptureDeviceInput(device: newCamera)
            }
            catch{
                print(error)
            }
            
            if let newVideoInput = newVideoInput{
                session?.addInput(newVideoInput)
            }
        }
    }
    
}

Hi @romanus your code is helpful, thanks!
I want to record a video in press button in this view how can i do any idea ?

Update:

import UIKit
import AVFoundation

class ViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    
    @IBOutlet weak var cameraView: UIView!
    
    var session: AVCaptureSession?
    var device: AVCaptureDevice?
    var input: AVCaptureDeviceInput?
    var output: AVCaptureMetadataOutput?
    var prevLayer: AVCaptureVideoPreviewLayer?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        createSession()
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        prevLayer?.frame.size = cameraView.frame.size
    }
    
    func createSession() {
        session = AVCaptureSession()
        device = AVCaptureDevice.default(for: AVMediaType.video)
        
        do{
            input = try AVCaptureDeviceInput(device: device!)
        }
        catch{
            print(error)
        }
        
        if let input = input{
            session?.addInput(input)
        }
        
        prevLayer = AVCaptureVideoPreviewLayer(session: session!)
        prevLayer?.frame.size = cameraView.frame.size
        prevLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill
        
        prevLayer?.connection?.videoOrientation = transformOrientation(orientation: UIInterfaceOrientation(rawValue: UIApplication.shared.statusBarOrientation.rawValue)!)
        
        cameraView.layer.addSublayer(prevLayer!)
        
        session?.startRunning()
    }
    
    func cameraWithPosition(position: AVCaptureDevice.Position) -> AVCaptureDevice? {
        if #available(iOS 11.1, *) {
        let deviceDiscoverySession = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInDualCamera, .builtInTelephotoCamera, .builtInTrueDepthCamera, .builtInWideAngleCamera, ], mediaType: .video, position: position)
        
        if let device = deviceDiscoverySession.devices.first {
            return device
        }
            else {
                //add code here
            }
        return nil
    }
    
    func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
        coordinator.animate(alongsideTransition: { (context) -> Void in
            self.prevLayer?.connection?.videoOrientation = self.transformOrientation(orientation: UIInterfaceOrientation(rawValue: UIApplication.shared.statusBarOrientation.rawValue)!)
            self.prevLayer?.frame.size = self.cameraView.frame.size
        }, completion: { (context) -> Void in
            
        })
        super.viewWillTransition(to: size, with: coordinator)
    }
        return device
    }
    
    func transformOrientation(orientation: UIInterfaceOrientation) -> AVCaptureVideoOrientation {
        switch orientation {
        case .landscapeLeft:
            return .landscapeLeft
        case .landscapeRight:
            return .landscapeRight
        case .portraitUpsideDown:
            return .portraitUpsideDown
        default:
            return .portrait
        }
    }
    
    @IBAction func switchCameraSide(sender: AnyObject) {
        if let sess = session {
            let currentCameraInput: AVCaptureInput = sess.inputs[0]
            sess.removeInput(currentCameraInput)
            var newCamera: AVCaptureDevice
            if (currentCameraInput as! AVCaptureDeviceInput).device.position == .back {
                newCamera = self.cameraWithPosition(position: .front)!
            } else {
                newCamera = self.cameraWithPosition(position: .back)!
            }
            
            var newVideoInput: AVCaptureDeviceInput?
            do{
                newVideoInput = try AVCaptureDeviceInput(device: newCamera)
            }
            catch{
                print(error)
            }
            
            if let newVideoInput = newVideoInput{
                session?.addInput(newVideoInput)
            }
        }
    }
    
}

Wow guys I just noticed that you're making updates in the comments! You are awesome! 🚀