Tab bar cause navigation controller bar button item customView disappear

Question

I have embedded two navigation controllers in a tab bar controller. The two navigation controllers both have a view controller. The two view controllers both have a right bar button item, and the two bar button items have been set customView with a static var sharedView, which conforms to a UIView inheritance. The sharedView has been set to yellow color.

I expect the two bar button items always show yellow color. However, when switching between the two tabs, the navigation bar button item will disappear once in every four switches.

I have made a sample project replicating this issue: https://github.com/lenameow/TestCustomView

Relevant code:

import Foundation import UIKit

class SharedView: UIView {
    static var sharedView = SharedView(frame: CGRect(x: 0, y: 0, width: 25, height: 25))
    
    func setupUI(button: UIBarButtonItem) {
        SharedView.sharedView.backgroundColor = UIColor.yellow
        button.customView = SharedView.sharedView
    }
}


class ViewController: UIViewController {

    @IBOutlet weak var testBarButton: UIBarButtonItem!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Do any additional setup after loading the view.
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(true)
        SharedView.sharedView.setupUI(button: testBarButton)
    }
}

class SecondViewController: UIViewController {

    @IBOutlet weak var testBarButton: UIBarButtonItem!
    
    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(true)
        SharedView.sharedView.setupUI(button: testBarButton)
    }
}

The storyboard structure

How it now acts (gif)

Thanks for any inputs.

Answer 1

Finally I found a way to bypass this issue by replacing the static var with separate variables in each VC. However, it is still unknown why using a static var would cause that phenomenon. I have submitted a report to Apple regarding this issue.