Why is this didSet property not printing any output in Swift? - swift

Question

I have correctly set up a UIPageViewController.
I would like to check the itemIndex of each views and display content accordingly. Here's what the code looks like:
var itemIndex: Int = 0 {
didSet {
if itemIndex == 1 {
println("Character is Lela!")
}
if itemIndex == 0 {
println("Character is John!")
}
}
}
What I tried
I run the app
Console Output: "Character is John!"
I swipe forward (to the right)
Console Output: "Character is Lela!"
I swipe back (to the left)
There is no output!
I swipe forward
There is no output! Again!
What is this due to? Here's the full code:
import UIKit
var currentIndex: Int = 0
var nextIndex: Int = 0
class ProView: UIViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {
var pageViewController: UIPageViewController?
let characterImages = ["character1", "character2", "character1", "character2", "character1", "character2", "character1", "character2"]
override func viewDidLoad() {
super.viewDidLoad()
createPageViewController()
setupPageControl()
character = 1
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
// Forward, check if this IS NOT the last controller
func pageViewController(pageViewController: UIPageViewController,
viewControllerAfterViewController ProView: UIViewController) -> UIViewController? {
let itemController = ProView as PageItemController
// Check if there is another view
if itemController.itemIndex+1 < characterImages.count {
return getItemController(itemController.itemIndex+1)
}
return nil
}
// Check if this IS NOT the first controller
func pageViewController(pageViewController: UIPageViewController,
viewControllerBeforeViewController ProView: UIViewController) -> UIViewController? {
let itemController = ProView as PageItemController
if itemController.itemIndex < 0 {
return getItemController(itemController.itemIndex-1)
}
return nil
}
private func getItemController(itemIndex: Int) -> PageItemController? {
if itemIndex < characterImages.count {
let pageItemController = self.storyboard!.instantiateViewControllerWithIdentifier("ItemController") as PageItemController
pageItemController.itemIndex = itemIndex
pageItemController.imageName = characterImages[itemIndex]
return pageItemController
}
return nil
}
func createPageViewController() {
let pageController = self.storyboard!.instantiateViewControllerWithIdentifier("PageController") as UIPageViewController
pageController.dataSource = self
pageController.delegate = self
if characterImages.count > 0 {
let firstController = getItemController(0)!
let startingViewControllers: NSArray = [firstController]
pageController.setViewControllers(startingViewControllers, direction: UIPageViewControllerNavigationDirection.Forward, animated: false, completion: nil)
}
pageViewController = pageController
addChildViewController(pageViewController!)
self.view.addSubview(pageViewController!.view)
pageViewController?.didMoveToParentViewController(self)
}
func setupPageControl() {
let appearance = UIPageControl.appearance()
appearance.pageIndicatorTintColor = UIColor.grayColor()
appearance.currentPageIndicatorTintColor = UIColor.whiteColor()
}
func presentationCountForPageViewController(pageViewController: UIPageViewController) -> Int {
return characterImages.count
}
func presentationIndexForPageViewController(pageViewController: UIPageViewController) -> Int {
return 0
}
// BETA
func pageViewController(PageItemController: UIPageViewController,
didFinishAnimating finished: Bool,
previousViewControllers pageViewController: [AnyObject],
transitionCompleted completed: Bool)
{
if (!completed)
{
// You do nothing because whatever page you thought
// the book was on before the gesture started is still the correct page
return;
}
// This is where you would know the page number changed and handle it appropriately
}
}
class PageItemController: UIViewController {
#IBOutlet weak var imageCharacterChoose: UIImageView!
var itemIndex: Int = 0 {
didSet {
if itemIndex == 1 {
println("Character is Lela!")
}
if itemIndex == 0 {
println("Character is John!")
}
}}
var imageName: String = "" {
didSet {
if let imageView = imageCharacterChoose {imageCharacterChoose.image = UIImage(named: imageName)
}
}
}
override func viewDidLoad() {
super.viewDidLoad()
imageCharacterChoose!.image = UIImage(named: imageName)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
}

Answer 1

didSet and willSet will only get called when you change the value of the corresponding variable, so in your case you should somewhere in your code do itemIndex = 1, or some other value to trigger the functions.