PageViewController current page index in Swift

Question

I want to get current index of a pageViewController, I don\'t know how I get the visible pages index.

func pageViewController(pageViewController: UIPageViewContr         


        

Answer 1

Swift 3: full programmatic PageViewController example to get/set the current page index without view tagging:

enum PageViewType:String {
        case green = "greenView"
        case blue = "blueView"
        case red = "redView"  
}

class MyPageViewController: UIPageViewController {

    private (set) lazy var orderedViewControllers:[UIViewController] = {
         return [self.newPageView(.green),
                self.newPageView(.blue),
                self.newPageView(.red)
        ]
    }

    var currentIndex:Int {
            get {
                return orderedViewControllers.index(of: self.viewControllers!.first!)!
            }

            set {
                guard newValue >= 0,
                    newValue < orderedViewControllers.count else {
                    return
                }

                let vc = orderedViewControllers[newValue]
                let direction:UIPageViewControllerNavigationDirection = newValue > currentIndex ? .forward : .reverse            
                self.setViewControllers([vc], direction: direction, animated: true, completion: nil) 
            }
        }

    override func viewDidLoad() {
        super.viewDidLoad()

        dataSource = self

        if let firstViewController = orderedViewControllers.first {
            setViewControllers([firstViewController],
                           direction: .forward,
                           animated: true,
                           completion: nil)
        }
    }

    private func newPageView(_ viewType:PageViewType) -> UIViewController {
        let vc = self.storyboard?.instantiateViewController(withIdentifier: viewType.rawValue)       
        return vc
    }
}

UIPageViewController DataSource implementation:

extension MyPageViewController:UIPageViewControllerDataSource {

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

        let previousIndex = currentIndex - 1

        guard previousIndex >= 0 else {
            return nil
        }

        guard orderedViewControllers.count > previousIndex else {
            return nil
        }

        return orderedViewControllers[previousIndex]   
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {         
        let nextIndex = currentIndex + 1

        guard orderedViewControllers.count != nextIndex else {
            return nil
        }

        guard orderedViewControllers.count > nextIndex else {
            return nil
        }

        return orderedViewControllers[nextIndex]
    }

    func presentationCountForPageViewController(pageViewController: UIPageViewController) -> Int {
        return orderedViewControllers.count
    }

    func presentationIndexForPageViewController(pageViewController: UIPageViewController) -> Int {

        return currentIndex
    }
}

Answer 2

You can use next method:

func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
    guard
        completed,
        let viewControllerIndex = tutorialViews.index(of: pageViewController.viewControllers!.first!) else
            return
        }

    self.currentIndex = viewControllerIndex
}

Where tutorialViews is an array of pages (ViewControllers).
And initialize currentIndex like that:

var currentIndex = 0 {
    didSet {
        self.updateContentForPage(withIndex: currentIndex)
    }
}

Answer 3

First, have your UIPageViewController implement the UIPageViewControllerDataSource method presentationIndex(for pageViewController: UIPageViewController) -> Int to return the index for each of the PageViewController's ViewControllers.

Then in your delegate, access the datasource through the passed-in PageViewController:

func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
    guard let dataSource = pageViewController.dataSource, 
          let currentIndex = dataSource.presentationIndex?(for: pageViewController) else { preconditionFailure() }

}

Answer 4

Swift 4 version

Extending the ViewController class with these protocols (UIPageViewControllerDelegate, UIPageViewControllerDataSource) and adding the following functions helped me to make my page control work correctly.

class ViewController : UIPageViewControllerDelegate,UIPageViewControllerDataSource {

    func pageViewController(_ pageViewController: UIPageViewController, willTransitionTo pendingViewControllers: [UIViewController]) {
        if let viewController = pendingViewControllers[0] as? DataViewController {
            self.lastPendingViewControllerIndex = viewController.index!
        }
    }

    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        if completed {
            pageControl.currentPage = self.lastPendingViewControllerIndex
            if lastPendingViewControllerIndex == 4 {
                self.getstartedButton.isHidden=false
            } else {
                self.getstartedButton.isHidden=true
            }
        }
    }
}

Answer 5

Just check apple's docs (https://developer.apple.com/tutorials/swiftui/interfacing-with-uikit) -> Section 3 -> Step 5

You can get the current index like this

func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
            if completed,
                let visibleViewController = pageViewController.viewControllers?.first,
                let index = parent.controllers.firstIndex(of: visibleViewController)
            {
                parent.currentPage = index
            }
        }

or if you are keeping viewControllers in an array you can do this

func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        if completed,
            let visibleViewController = pageViewController.viewControllers?.first,
            let index = orderedViewControllers.firstIndex(of: visibleViewController)
        {
            statisticsPageDelegate?.statisticsPageViewController(statisticsPageViewController: self, didUpdatePageIndex: index)
        }
    }

This is the full code

class StatisticsPageViewController: UIPageViewController,UIPageViewControllerDataSource, UIPageViewControllerDelegate {

    var currentIndex: Int?
    var statisticsPageDelegate: StatisticsPageViewControllerDelegate?
    private var pendingIndex: Int?

    required init?(coder aDecoder: NSCoder) {
        super.init(transitionStyle: .scroll, navigationOrientation: .horizontal, options: nil)
    }
    override func viewDidLoad() {
        super.viewDidLoad()
        dataSource = self
        delegate = self

        if let firstViewController = orderedViewControllers.first {
            setViewControllers([firstViewController],
                               direction: .forward,
                               animated: true,
                               completion: nil)
        }

        statisticsPageDelegate?.statisticsPageViewController(
            statisticsPageViewController: self,
            didUpdatePageCount: orderedViewControllers.count
        )
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        guard let viewControllerIndex = orderedViewControllers.index(of:viewController) else {
            return nil
        }

        let previousIndex = viewControllerIndex - 1

        guard previousIndex >= 0 else {
            return nil
        }

        guard orderedViewControllers.count > previousIndex else {
            return nil
        }

        return orderedViewControllers[previousIndex]
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        guard let viewControllerIndex = orderedViewControllers.index(of:viewController) else {
            return nil
        }

        let nextIndex = viewControllerIndex + 1
        let orderedViewControllersCount = orderedViewControllers.count

        guard orderedViewControllersCount != nextIndex else {
            return nil
        }

        guard orderedViewControllersCount > nextIndex else {
            return nil
        }

        return orderedViewControllers[nextIndex]
    }

    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        if completed,
            let visibleViewController = pageViewController.viewControllers?.first,
            let index = orderedViewControllers.firstIndex(of: visibleViewController)
        {
            statisticsPageDelegate?.statisticsPageViewController(statisticsPageViewController: self, didUpdatePageIndex: index)
        }
    }

    private(set) lazy var orderedViewControllers: [UIViewController] = {
        return [self.newStatisticsViewController(identifier: Identifiers.PROGRAM_VIEW_CONTROLLER),
        self.newStatisticsViewController(identifier: Identifiers.LOGIN_VIEW_CONTROLLER)]
    }()

    private func newStatisticsViewController(identifier: String) -> UIViewController {
        return UIStoryboard(name: "Main", bundle: nil) .
            instantiateViewController(withIdentifier: identifier)
    }
}

protocol StatisticsPageViewControllerDelegate: class {
    func statisticsPageViewController(statisticsPageViewController:
        StatisticsPageViewController, didUpdatePageCount count: Int)
    func statisticsPageViewController(statisticsPageViewController:
        StatisticsPageViewController, didUpdatePageIndex index: Int)
}

Answer 6

Add this code to your UIPageViewController.

var pages = [UIViewController]()
var currentIndex: Int {
    guard let vc = viewControllers?.first else { return 0 }
    return pages.firstIndex(of: vc) ?? 0
}