removeViewControllerBehind.swift

//
//  ViewController.swift
//  Created by Woody on 2021/1/28.

/*
a simple example for removing the superimposed ViewController behind
*/

import UIKit

class ViewController: UIViewController {
    
    lazy var button: UIButton = {
        let b =  UIButton()
        b.setTitle("GO", for: .normal)
        b.addTarget(self, action: #selector(press), for: .touchUpInside)
        b.setTitleColor(.red, for: .normal)
        b.backgroundColor = .white
        return b
    }()
        
        
       
    
    

    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(button)
        button.translatesAutoresizingMaskIntoConstraints = false
        button.heightAnchor.constraint(equalToConstant: 50).isActive = true
        button.widthAnchor.constraint(equalToConstant: 50).isActive = true
        button.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        button.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true

        
    }


    
    private func getViewController()-> UIViewController {
        
        let vc = ViewController()
        vc.view.backgroundColor = .blue
    
        return vc
    }
    
    
    
    /// point this order, The first step is push New ViewController
    @objc func press() {
        let vc = getViewController()
        navigationController?.pushViewController(vc, animated: true)
        removeSurplusViewController()
    }
    
    
    private func removeSurplusViewController() {
        guard let viewControllers = self.navigationController?.viewControllers, viewControllers.count >= 3 else { return }
        
        for vc in viewControllers where vc.view.backgroundColor == UIColor.blue {
            // filter the specific ViewController and remove unnecessary others
            guard let count = navigationController?.viewControllers.filter({ $0.view.backgroundColor == UIColor.blue }).count
            , count > 1 else { return }
            
            // find the index from navigationController?.viewControllers
            if let index = self.navigationController?.viewControllers.firstIndex(of: vc){
                self.navigationController?.viewControllers.remove(at: index)
            }
        }
    }
    
    
    
    
}