View doesn't show with "setViewController" in a UIPageViewController in Swift - ios

Question

I would like to change the pages showed by my UIPageView programatically.
I created two ViewController that are intended to be displayed in the PageView, and I set the initial View with "setViewControllers" in my viewDidLoad. I works, the view is displayed and I can swipe on the screen to switch between the two views.
My problem being that when I try to call again "setViewControllers" to change the displayed view when I click a button, nothing happens.
I'm using delegates since the buttons are part of another ViewController, and used NSLog to make sure the functions were called, which is the case.
If anyone could help me understand why the "setViewControllers" method doesn't do anything, that would be great.
Here is my code for my UIPageViewController:
import UIKit
class FrontContentController: UIPageViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate, sideMenuDelegate {
func presentationCount(for pageViewController: UIPageViewController) -> Int {
return subViewControllers.count
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
let currentIndex:Int = subViewControllers.index(of: viewController) ?? 0
if currentIndex <= 0 {
return nil
}
return subViewControllers[currentIndex - 1]
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
let currentIndex:Int = subViewControllers.index(of: viewController) ?? 0
if currentIndex >= subViewControllers.count - 1 {
return nil
}
return subViewControllers[currentIndex + 1]
}
lazy var subViewControllers:[UIViewController] = {
return [
UIStoryboard(name: "frontPage", bundle: nil).instantiateViewController(withIdentifier: "FirstContent") as! FirstContentController,
UIStoryboard(name: "frontPage", bundle: nil).instantiateViewController(withIdentifier: "SecondContent") as! SecondContentController
]
}()
var sideMenuVC : SideMenuController!
override func viewDidLoad() {
super.viewDidLoad()
self.delegate = self
self.dataSource = self
self.sideMenuVC = (self.storyboard?.instantiateViewController(withIdentifier: "SideMenu") as! SideMenuController)
self.setViewControllers([subViewControllers[0]], direction: .forward, animated: true, completion: nil)
// Do any additional setup after loading the view.
}
func changeColor(_ color: UIColor) {
if color == .blue {
self.setViewControllers([subViewControllers[0]], direction: .forward, animated: false, completion: nil)
NSLog("Blue Delegate")
}
if color == .red {
self.setViewControllers([subViewControllers[1]], direction: .forward, animated: false, completion: nil)
NSLog("Red Delegate")
}
}
}
And in case it's relevant, the separate UIViewController with the buttons (a side menu) :
import UIKit
protocol sideMenuDelegate: AnyObject {
func changeColor(_ color : UIColor)
}
class SideMenuController: UIViewController {
weak var delegate : sideMenuDelegate?
var frontPageVC : FrontPageController!
var frontContentPC : FrontContentController!
override func viewDidLoad() {
super.viewDidLoad()
let storyboard = UIStoryboard(name: "frontPage", bundle: nil)
frontPageVC = (storyboard.instantiateViewController(withIdentifier: "FrontPage") as! FrontPageController)
frontContentPC = (storyboard.instantiateViewController(withIdentifier: "FrontContent") as! FrontContentController)
self.delegate = frontContentPC
self.view.backgroundColor = UIColor.black
}
#IBAction func pressBlueButton(_ sender: Any) {
delegate?.changeColor(UIColor .blue)
}
#IBAction func pressRedButton(_ sender: Any) {
delegate?.changeColor(UIColor .red)
}
}
Thanks