Add Indicator View over tab bar item. (Swift 5)

TabBarIndicatorView.swift

//
//  Created by Egzon Pllana on 13.4.23.
//  Copyright © 2023 Native Coders. All rights reserved.
//

import UIKit

class IndicatingTabBarController: UITabBarController, UITabBarControllerDelegate {

    // MARK: - Properties -

    private let indicatorView: UIView = {
        let view = UIView()
        view.backgroundColor = .black
        return view
    }()

    // Set attributes as you need here
    private lazy var indicatorWidth: Double = tabBar.bounds.width / CGFloat(tabBar.items?.count ?? 1)
    private var indicatorColor: UIColor = .black

    // MARK: - Life cycle -

    override func viewDidLoad() {
        super.viewDidLoad()
        // Add the line indicator as a subview of the tab bar
        tabBar.addSubview(indicatorView)
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        // Position the line indicator at the bottom of the selected tab item
        moveIndicator()
    }

    // MARK: - Methods -

    func moveIndicator(at index: Int=0) {
        let itemWidth = (tabBar.bounds.width / CGFloat(tabBar.items?.count ?? 1))
        let xPosition = (CGFloat(index) * itemWidth) + ((itemWidth / 2) - (indicatorWidth / 2))

        UIView.animate(withDuration: 0.3) { [self] in
            self.indicatorView.frame = CGRect(x: xPosition,
                                              y: 1,
                                              width: self.indicatorWidth,
                                              height: 1)
            self.indicatorView.backgroundColor = self.indicatorColor
        }
    }

    // MARK: - UITabBarControllerDelegate -

    override func tabBar(_ tabBar: UITabBar, didSelect item: UITabBarItem) {
        guard let items = tabBar.items else { return }
        moveIndicator(at: items.firstIndex(of: item) ?? 0)
    }
}

// ------- How to use ------- //

// Step 1:
// Create new file: TabBarController

class TabBarController: IndicatingTabBarController {
    
    // MARK: - Life cycle -

    override func viewDidLoad() {
        super.viewDidLoad()
    }
}
// Step 2:
// In storyboard, select tab bar controller and set its class to TabBarController.

// ------- Additional ------- //

// If you need to listen to tab bar delegate method didSelect, please do:

class TabBarController: IndicatingTabBarController {

    // MARK: - Life cycle -

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // MARK: - UITabBarControllerDelegate
    
    override func tabBar(_ tabBar: UITabBar, didSelect item: UITabBarItem) {
        guard let items = tabBar.items else { return }
        moveIndicator(at: items.firstIndex(of: item) ?? 0)
    }
}

// Note: 
// If you want to customize tab bar indicating view color, width, height, position, 
// please do it inside IndicatingTabBarController.

@uzair045 update the whole implementation, now it should be working fine.