PageViewController - Pass variables to child views

What I have

I have a ViewController (TutorialViewController) and a UIPageViewController (TutorialPageViewController). There are also 3 extra views on the storyboard with StoryBoard ID's:

GreenViewController
BlueViewController
RedViewController

I have been following this tutorial (Kudos to the author, very well written).

On the Green View Controller I have defined a variable:

var passedVariable = ""

And in the ViewDidLoad I print it out.

Here are the two controllers that have the code:

UIViewController (TutorialViewController):

class TutorialViewController: UIViewController {

@IBOutlet weak var pageControl: UIPageControl!
@IBOutlet weak var containerView: UIView!


var tutorialPageViewController: TutorialPageViewController? {
    didSet {
        tutorialPageViewController?.tutorialDelegate = self
    }
}


override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if let tutorialPageViewController = segue.destinationViewController as? TutorialPageViewController {
        self.tutorialPageViewController = tutorialPageViewController
    }
}

@IBAction func didTapNextButton(sender: UIButton) {
    tutorialPageViewController?.scrollToNextViewController()
}
}

extension TutorialViewController: TutorialPageViewControllerDelegate {

func tutorialPageViewController(tutorialPageViewController: TutorialPageViewController,
    didUpdatePageCount count: Int) {
    pageControl.numberOfPages = count
}

func tutorialPageViewController(tutorialPageViewController: TutorialPageViewController,
    didUpdatePageIndex index: Int) {
    pageControl.currentPage = index
}

}

UIPageViewController

class TutorialPageViewController: UIPageViewController {

weak var tutorialDelegate: TutorialPageViewControllerDelegate?

//let vc0 = GreenViewController(nibName: "GreenViewController", bundle: nil)

private(set) lazy var orderedViewControllers: [UIViewController] = {
    // The view controllers will be shown in this order
    return [self.newColoredViewController("Green"),
        self.newColoredViewController("Red"),
        self.newColoredViewController("Blue"), self.newColoredViewController("Pink")]
}()

override func viewDidLoad() {
    super.viewDidLoad()

    //self.vc0.passedVariable = "Passed Data"

    dataSource = self
    delegate = self

    if let initialViewController = orderedViewControllers.first {
        scrollToViewController(initialViewController)
    }

    tutorialDelegate?.tutorialPageViewController(self,
        didUpdatePageCount: orderedViewControllers.count)
}


/**
 Scrolls to the next view controller.
 */
func scrollToNextViewController() {
    if let visibleViewController = viewControllers?.first,
        let nextViewController = pageViewController(self,
            viewControllerAfterViewController: visibleViewController) {
                scrollToViewController(nextViewController)
    }
}

private func newColoredViewController(color: String) -> UIViewController {
    return UIStoryboard(name: "Main", bundle: nil) .
        instantiateViewControllerWithIdentifier("\(color)ViewController")
}

/**
 Scrolls to the given 'viewController' page.

 - parameter viewController: the view controller to show.
 */
private func scrollToViewController(viewController: UIViewController) {
    setViewControllers([viewController],
        direction: .Forward,
        animated: true,
        completion: { (finished) -> Void in
            // Setting the view controller programmatically does not fire
            // any delegate methods, so we have to manually notify the
            // 'tutorialDelegate' of the new index.
            self.notifyTutorialDelegateOfNewIndex()
    })
}

/**
 Notifies '_tutorialDelegate' that the current page index was updated.
 */
private func notifyTutorialDelegateOfNewIndex() {
    if let firstViewController = viewControllers?.first,
        let index = orderedViewControllers.indexOf(firstViewController) {
            tutorialDelegate?.tutorialPageViewController(self,
                didUpdatePageIndex: index)
    }
}

}

// MARK: UIPageViewControllerDataSource

extension TutorialPageViewController: UIPageViewControllerDataSource {

func pageViewController(pageViewController: UIPageViewController,
    viewControllerBeforeViewController viewController: UIViewController) -> UIViewController? {
        guard let viewControllerIndex = orderedViewControllers.indexOf(viewController) else {
            return nil
        }

        let previousIndex = viewControllerIndex - 1

        // User is on the first view controller and swiped left to loop to
        // the last view controller.
        guard previousIndex >= 0 else {
            return orderedViewControllers.last
        }

        guard orderedViewControllers.count > previousIndex else {
            return nil
        }

        return orderedViewControllers[previousIndex]
}

func pageViewController(pageViewController: UIPageViewController,
    viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
        guard let viewControllerIndex = orderedViewControllers.indexOf(viewController) else {
            return nil
        }

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

        // User is on the last view controller and swiped right to loop to
        // the first view controller.
        guard orderedViewControllersCount != nextIndex else {
            return orderedViewControllers.first
        }

        guard orderedViewControllersCount > nextIndex else {
            return nil
        }

        return orderedViewControllers[nextIndex]
}

}

extension TutorialPageViewController: UIPageViewControllerDelegate {

func pageViewController(pageViewController: UIPageViewController,
    didFinishAnimating finished: Bool,
    previousViewControllers: [UIViewController],
    transitionCompleted completed: Bool) {
    notifyTutorialDelegateOfNewIndex()
}

}

protocol TutorialPageViewControllerDelegate: class {

/**
 Called when the number of pages is updated.

 - parameter tutorialPageViewController: the TutorialPageViewController instance
 - parameter count: the total number of pages.
 */
func tutorialPageViewController(tutorialPageViewController: TutorialPageViewController,
    didUpdatePageCount count: Int)

/**
 Called when the current index is updated.

 - parameter tutorialPageViewController: the TutorialPageViewController instance
 - parameter index: the index of the currently visible page.
 */
func tutorialPageViewController(tutorialPageViewController: TutorialPageViewController,
    didUpdatePageIndex index: Int)

}

What I have tried

I have tried declaring the View Controller first like so:

let vc0 = GreenViewController(nibName: "GreenViewController", bundle: nil)

And then passing the data like so:

override func viewDidLoad() {
   vc0.passedVariable = "This was passed, Dance with Joy"
}

Nothing is printing out in the console.

I also tried changing the bundle above to:

bundle: NSBundle.mainBundle()

Still nada

Question

I plan to load data on the TutorialViewController from an alamofire request, I want to pass that data to one of the ViewControllers (green, blue, red)

How do I pass data that has been acquired from the TutorialViewController to one of the child views that will load?

Solution

First, I want to thank you for checking out my tutorial and all of the nice things you said about it.

Second, I have a solution for you! I went ahead and committed the solution to the GitHub repo I linked in the tutorial. I will also post the code here.

(1) Create a UIViewController subclass to add custom properties to. For this example, I chose to add a UILabel since it's the easiest to view when running the app.

class ColoredViewController: UIViewController {

    @IBOutlet weak var label: UILabel!

}

(2) Inside Main.storyboard, change the custom class for each UIViewController "page" to ColoredViewController in the Identity Inspector.

(3) Add a UILabel to each "page" and constraint it however you'd like. I chose to vertically and horizontally center it in the container. Don't forget to link the UILabel to ColoredViewController's @IBOutlet weak var label: UILabel!.

(4) Optional: I deleted the default "Label" text in each one that way if we never set the label's text in code, we will not show "Label" to the user.

(5) We need to do some TLC to TutorialPageViewController so it knows that orderedViewControllers is now a ColoredViewController array. To make things easy, I'm just going to paste the entire class:

class TutorialPageViewController: UIPageViewController {

    weak var tutorialDelegate: TutorialPageViewControllerDelegate?

    private(set) lazy var orderedViewControllers: [ColoredViewController] = {
        // The view controllers will be shown in this order
        return [self.newColoredViewController("Green"),
            self.newColoredViewController("Red"),
            self.newColoredViewController("Blue")]
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        dataSource = self
        delegate = self

        if let initialViewController = orderedViewControllers.first {
            scrollToViewController(initialViewController)
        }

        tutorialDelegate?.tutorialPageViewController(self,
            didUpdatePageCount: orderedViewControllers.count)
    }

    /**
     Scrolls to the next view controller.
     */
    func scrollToNextViewController() {
        if let visibleViewController = viewControllers?.first,
            let nextViewController = pageViewController(self,
                viewControllerAfterViewController: visibleViewController) {
                    scrollToViewController(nextViewController)
        }
    }

    private func newColoredViewController(color: String) -> ColoredViewController {
        return UIStoryboard(name: "Main", bundle: nil) .
            instantiateViewControllerWithIdentifier("\(color)ViewController") as! ColoredViewController
    }

    /**
     Scrolls to the given 'viewController' page.

     - parameter viewController: the view controller to show.
     */
    private func scrollToViewController(viewController: UIViewController) {
        setViewControllers([viewController],
            direction: .Forward,
            animated: true,
            completion: { (finished) -> Void in
                // Setting the view controller programmatically does not fire
                // any delegate methods, so we have to manually notify the
                // 'tutorialDelegate' of the new index.
                self.notifyTutorialDelegateOfNewIndex()
        })
    }

    /**
     Notifies '_tutorialDelegate' that the current page index was updated.
     */
    private func notifyTutorialDelegateOfNewIndex() {
        if let firstViewController = viewControllers?.first as? ColoredViewController,
            let index = orderedViewControllers.indexOf(firstViewController) {
                tutorialDelegate?.tutorialPageViewController(self,
                    didUpdatePageIndex: index)
        }
    }

}

// MARK: UIPageViewControllerDataSource

extension TutorialPageViewController: UIPageViewControllerDataSource {

    func pageViewController(pageViewController: UIPageViewController,
        viewControllerBeforeViewController viewController: UIViewController) -> UIViewController? {
            guard let coloredViewController = viewController as? ColoredViewController,
                let viewControllerIndex = orderedViewControllers.indexOf(coloredViewController) else {
                return nil
            }

            let previousIndex = viewControllerIndex - 1

            // User is on the first view controller and swiped left to loop to
            // the last view controller.
            guard previousIndex >= 0 else {
                return orderedViewControllers.last
            }

            guard orderedViewControllers.count > previousIndex else {
                return nil
            }

            return orderedViewControllers[previousIndex]
    }

    func pageViewController(pageViewController: UIPageViewController,
        viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
            guard let coloredViewController = viewController as? ColoredViewController,
                let viewControllerIndex = orderedViewControllers.indexOf(coloredViewController) else {
                return nil
            }

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

            // User is on the last view controller and swiped right to loop to
            // the first view controller.
            guard orderedViewControllersCount != nextIndex else {
                return orderedViewControllers.first
            }

            guard orderedViewControllersCount > nextIndex else {
                return nil
            }

            return orderedViewControllers[nextIndex]
    }

}

extension TutorialPageViewController: UIPageViewControllerDelegate {

    func pageViewController(pageViewController: UIPageViewController,
        didFinishAnimating finished: Bool,
        previousViewControllers: [UIViewController],
        transitionCompleted completed: Bool) {
        notifyTutorialDelegateOfNewIndex()
    }

}

protocol TutorialPageViewControllerDelegate: class {

    /**
     Called when the number of pages is updated.

     - parameter tutorialPageViewController: the TutorialPageViewController instance
     - parameter count: the total number of pages.
     */
    func tutorialPageViewController(tutorialPageViewController: TutorialPageViewController,
        didUpdatePageCount count: Int)

    /**
     Called when the current index is updated.

     - parameter tutorialPageViewController: the TutorialPageViewController instance
     - parameter index: the index of the currently visible page.
     */
    func tutorialPageViewController(tutorialPageViewController: TutorialPageViewController,
        didUpdatePageIndex index: Int)

}

(6) Inside TutorialViewController: let's set the label.text. I chose to use viewDidLoad, but feel free to stuff this logic inside a network request completion block.

override func viewDidLoad() {
    super.viewDidLoad()

    if let greenColoredViewController = tutorialPageViewController?.orderedViewControllers.first {
        greenColoredViewController.label.text = "Hello world!"
    }
}

Hope this helps!