extension UITabBarController {
    
    func addSubviewToLastTabItem(_ imageName: String) {
        if let lastTabBarButton = self.tabBar.subviews.last, let tabItemImageView = lastTabBarButton.subviews.first {
            if let accountTabBarItem = self.tabBar.items?.last {
                accountTabBarItem.selectedImage = nil
                accountTabBarItem.image = nil
            }
            let imgView = UIImageView()
            imgView.frame = tabItemImageView.frame
            imgView.layer.cornerRadius = tabItemImageView.frame.height/2
            imgView.layer.masksToBounds = true
            imgView.contentMode = .scaleAspectFill
            imgView.clipsToBounds = true
            imgView.image = UIImage(named: imageName)
            self.tabBar.subviews.last?.addSubview(imgView)
        }
    }
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    self.tabBarController?.addSubviewToLastTabItem("profile")
}

In this post we are going to learn how to add a subview under UITabBarController in swift 5.

import UIKit

class TabBarSwitchView: UIView {
    
    let onColor = UIColor(hex: 0xF9CF2D)
    
    let offColor = UIColor.white
    
    let deselectColor = UIColor(hex: 0xBFBFBF)
    
    let bgColor = UIColor(hex: 0x404040)
    
    var travellerLabel: UILabel = {
        let v = UILabel()
        v.translatesAutoresizingMaskIntoConstraints = false
        return v
    }()
    
    var hostLabel: UILabel = {
        let v = UILabel()
        v.translatesAutoresizingMaskIntoConstraints = false
        return v
    }()
    
    var switchButton: UISwitch = {
        let v = UISwitch()
        v.isUserInteractionEnabled = false
        v.translatesAutoresizingMaskIntoConstraints = false
        return v
    }()
    
    var ison: Bool = false {
        didSet {
            isTraveller = !ison
            switchButton.setOn(ison, animated: true)
            if ison {
                hostLabel.textColor = onColor
                travellerLabel.textColor = deselectColor
            }else {
                hostLabel.textColor = deselectColor
                travellerLabel.textColor = offColor
            }
        }
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupViews()
    }
    
    let scale:CGFloat = 0.6
    
    func setupViews() {
        self.backgroundColor = bgColor
        self.addSubview(switchButton)
        switchButton.centerXAnchor.constraint(equalTo: centerXAnchor, constant: 0).isActive = true
        switchButton.centerYAnchor.constraint(equalTo: centerYAnchor, constant: 0).isActive = true
        switchButton.onTintColor = onColor
        switchButton.tintColor = UIColor.white
        switchButton.thumbTintColor = bgColor
        switchButton.layoutIfNeeded()
        switchButton.backgroundColor = offColor
        switchButton.layer.cornerRadius = 16
        switchButton.transform = CGAffineTransform(scaleX: scale, y: scale)
        
        self.addSubview(travellerLabel)
        travellerLabel.centerYAnchor.constraint(equalTo: centerYAnchor, constant: 0).isActive = true
        travellerLabel.trailingAnchor.constraint(equalTo: switchButton.leadingAnchor, constant: -8).isActive = true
        travellerLabel.text = "TRAVELLER"
        travellerLabel.font = UIFont.systemFont(ofSize: 12)
        travellerLabel.textColor = UIColor.white
        
        self.addSubview(hostLabel)
        hostLabel.centerYAnchor.constraint(equalTo: centerYAnchor, constant: 0).isActive = true
        hostLabel.leadingAnchor.constraint(equalTo: switchButton.trailingAnchor, constant: 8).isActive = true
        hostLabel.text = "HOST"
        hostLabel.font = UIFont.systemFont(ofSize: 12)
        hostLabel.textColor = onColor
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
}

import UIKit

var isTraveller = false
class TabBarRootVC: UIViewController {

    private lazy var tabBarVC: CustomTabBarVC = {
        var viewController = CustomTabBarVC()
        return viewController
    }()
    
    var bottomHeight: CGFloat {
        guard #available(iOS 11.0, *),
            let window = UIApplication.shared.keyWindow else {
                return 0
        }
        return window.safeAreaInsets.bottom
    }
    
    var switchView: TabBarSwitchView = {
        let v = TabBarSwitchView()
        v.translatesAutoresizingMaskIntoConstraints = false
        return v
    }()
    
    var hideBottomBar: Bool = false {
        didSet {
            if hideBottomBar {
                heightConstraint.constant = 0
            }else {
                heightConstraint.constant = 32 + bottomHeight
            }
            UIView.animate(withDuration: 0.3) {
                self.view.layoutIfNeeded()
            }
        }
    }
    
    var heightConstraint: NSLayoutConstraint!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupViews()
    }
    
    func setupViews() {
        self.view.backgroundColor = UIColor.white
        self.view.addSubview(switchView)
        switchView.edges([.left, .right, .bottom], to: self.view, offset: .zero)
        heightConstraint = switchView.heightAnchor.constraint(equalToConstant: 32 + bottomHeight)
        heightConstraint.isActive = true
        switchView.ison = false
        switchView.isUserInteractionEnabled = true
        switchView.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(switchViewTapped(recognizer:))))
        
        addChild(tabBarVC)
        self.view.addSubview(tabBarVC.view)
        tabBarVC.view.translatesAutoresizingMaskIntoConstraints = false
        tabBarVC.view.edges([.left, .right, .top], to: self.view, offset: .zero)
        tabBarVC.view.bottomAnchor.constraint(equalTo: switchView.topAnchor, constant: 0).isActive = true
        tabBarVC.didMove(toParent: self)
        if !hideBottomBar {
            heightConstraint.constant = 32 + bottomHeight
        }else {
            heightConstraint.constant = 0
        }
        
    }
    
    @objc func switchViewTapped(recognizer: UITapGestureRecognizer) {
        switchView.ison = !switchView.ison
        isTraveller = !switchView.ison
        NotificationCenter.default.post(name: Notification.Name(rawValue: "switchChanged"), object: nil)
    }
    

}

extension UIViewController {
    func hideBottomSwitch(_ hide: Bool) {
        if let customTab = self.tabBarController as? CustomTabBarVC {
            customTab.hideSwitch = hide
        }
    }
}

var hideSwitch: Bool = false {
    didSet {
        print("view")
        if let parentVc = self.parent as? TabBarRootVC {
            parentVc.hideBottomBar = hideSwitch
        }
    }
}

import UIKit

class HomeViewController: UIViewController {
    
    var tableView: UITableView = {
        let v = UITableView()
        v.translatesAutoresizingMaskIntoConstraints = false
        return v
    }()
    
    var dataSource = [Place]()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.navigationItem.title = "Home"
        dataSource = [Place(name: "Ocean view during daylight", hostName: "Carey", imageName: "Ocean", createdOn: "23th Mar 2019"), Place(name: "Coconut palm trees", hostName: "Stark", imageName: "Trees", createdOn: "13th Mar 2019"), Place(name: "Trees in park", hostName: "Micheal", imageName: "Park", createdOn: "28th Feb 2019"), Place(name: "Water under sunset", hostName: "Shiny", imageName: "Sunset", createdOn: "16th Feb 2019"), Place(name: "Green trees beside roadway", hostName: "Nina", imageName: "Forest", createdOn: "1st Feb 2019")]
        setupViews()
        NotificationCenter.default.addObserver(self, selector: #selector(switchChanged), name:  Notification.Name(rawValue: "switchChanged"), object: nil)
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        self.hideBottomSwitch(false)
    }
    
    func setupViews() {
        self.navigationController?.navigationBar.isTranslucent = false
        view.addSubview(tableView)
        tableView.edges([.all], to: view.safeAreaLayoutGuide, offset: .zero)
        tableView.contentInsetAdjustmentBehavior = .never
        tableView.separatorStyle = .singleLine
        tableView.separatorInset = .zero
        tableView.delegate = self
        tableView.dataSource = self
        tableView.register(CustomTableViewCell.self, forCellReuseIdentifier: CellIds.hostCellId)
        tableView.register(CustomTableViewCell.self, forCellReuseIdentifier: CellIds.travellerCellId)
    }
    
    @objc func switchChanged() {
        self.tableView.reloadData()
    }
}

extension HomeViewController: UITableViewDelegate {
    
    func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return UITableView.automaticDimension
    }
    
    func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
        return 80
    }
    
    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        let vc = DetailViewController()
        vc.place = dataSource[indexPath.row]
        vc.hidesBottomBarWhenPushed = true
        self.hideBottomSwitch(true)
        self.navigationController?.pushViewController(vc, animated: true)
    }
    
}

extension HomeViewController: UITableViewDataSource {
    
    func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return dataSource.count
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        if isTraveller {
            // Traveller Cell
            let cell = tableView.dequeueReusableCell(withIdentifier: CellIds.travellerCellId, for: indexPath) as! CustomTableViewCell
            let itemAtIndex = dataSource[indexPath.row]
            cell.imgView.image = UIImage(named: itemAtIndex.imageName)
            cell.txtLabel.text = itemAtIndex.name
            cell.subtitleLabel.text = itemAtIndex.hostName
            cell.selectionStyle = .none
            return cell
        }else {
            // Host Cell
            let cell = tableView.dequeueReusableCell(withIdentifier: CellIds.hostCellId, for: indexPath) as! CustomTableViewCell
            let itemAtIndex = dataSource[indexPath.row]
            cell.imgView.image = UIImage(named: itemAtIndex.imageName)
            cell.txtLabel.text = itemAtIndex.name
            cell.subtitleLabel.text = itemAtIndex.createdOn
            cell.selectionStyle = .none
            return cell
        }
    }
    
}

Now run the project we will see output as following:

Download the finished project from the following link: