UIPageViewController crashing when not using static data - ios

Question

I have a working page view controller system with this ( just going to paste absolutely everything, pretty sure the issue just lies in my firebase observation near the top) :
class IndividualPeopleVC: UIViewController, UIPageViewControllerDataSource {
var pageViewController: UIPageViewController!
var pageTitles : [String]!
var imageURLS: NSArray!
let currentUser = FIRAuth.auth()?.currentUser?.uid
override func viewDidLoad()
{
super.viewDidLoad()
self.pageTitles = []
self.pageTitles = ["1", "2", "3", "4'"]
DataService.ds.REF_INTERESTS.child(passedInterest).child("rooms").child(passedRoom).child("users").observeSingleEventOfType(.Value) { (snapshot: FIRDataSnapshot) in
print(snapshot.value)
if let snapshots = snapshot.children.allObjects as? [FIRDataSnapshot] {
for snap in snapshots {
let name = snap.key
let uid = snap.value as! String
let person = Person(name: name, bio: "", UID: uid)
if person.UID != self.currentUser {
self.pageTitles.append(uid)
}
}
}
self.pageViewController = self.storyboard?.instantiateViewControllerWithIdentifier("PageViewController") as! UIPageViewController
self.pageViewController.dataSource = self
let startVC = self.viewControllerAtIndex(0) as ContentViewController
let viewControllers = NSArray(object: startVC)
self.pageViewController.setViewControllers(viewControllers as? [UIViewController], direction: .Forward, animated: true, completion: nil)
self.pageViewController.view.frame = CGRectMake(0, 30, self.view.frame.width, self.view.frame.size.height - 60)
self.addChildViewController(self.pageViewController)
self.view.addSubview(self.pageViewController.view)
self.pageViewController.didMoveToParentViewController(self)
}
func viewControllerAtIndex(index: Int) -> ContentViewController
{
if ((self.pageTitles.count == 0) || (index >= self.pageTitles.count)) {
return ContentViewController()
}
var vc: ContentViewController = self.storyboard?.instantiateViewControllerWithIdentifier("ContentViewController") as! ContentViewController
vc.titleText = self.pageTitles[index] as! String
vc.imageFile = self.pageImages[index] as! String
vc.pageIndex = index
return vc
}
func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController?
{
var vc = viewController as! ContentViewController
var index = vc.pageIndex as Int
if (index == 0 || index == NSNotFound)
{
return nil
}
index--
return self.viewControllerAtIndex(index)
}
func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
var vc = viewController as! ContentViewController
var index = vc.pageIndex as Int
if (index == NSNotFound) {
return nil
}
index++
if (index == self.pageTitles.count){
return nil
}
return self.viewControllerAtIndex(index)
}
func presentationCountForPageViewController(pageViewController: UIPageViewController) -> Int{
return self.pageTitles.count
}
func presentationIndexForPageViewController(pageViewController: UIPageViewController) -> Int{
return 0
}
}
So basically most of that is just copy-pasted from another source and it works. It creates 4 pages from the pageTitles array that scroll and on another VC I am passing the 1,2,3 and 4 and a label is displaying everything in the array as the scrollview should.
The problem comes when I try to not hard-code the pageTitles and instead pull it from firebase.
When I comment out where I'm hard-coding the pageTitles array, I get an unexpected nil value on my ContentViewController where I'm sending the titles and I do like titleLabel.text = (what was sent over).
I figured maybe guarding it with an if/let to allow firebase time to load stuff in would help, so I did a
if let title = (what was sent over) {
titleLabel.text = title
}
Nothing shows up on the screen when this happens, and then if I scroll left or right I get an error with indexes down in my pagebefore/pageafters.
I feel like this should be super simple and very similar to a tableview? Load in data from firebase, fill an array with the info, use if/lets to allow firebase some time to load in, then update the UI based on the array.

Answer 1

I think your DataService is asynchronous. You have to create your pageviewcontroller once your data is ready. Try this modified viewDidLoad method.
override func viewDidLoad()
{
super.viewDidLoad()
self.pageTitles = []
// self.pageTitles = ["1", "2", "3", "4'"]
DataService.ds.REF_INTERESTS.child(passedInterest).child("rooms").child(passedRoom).child("users").observeSingleEventOfType(.Value) { (snapshot: FIRDataSnapshot) in
print(snapshot.value)
if let snapshots = snapshot.children.allObjects as? [FIRDataSnapshot] {
for snap in snapshots {
let name = snap.key
let uid = snap.value as! String
let person = Person(name: name, bio: "", UID: uid)
if person.UID != self.currentUser {
self.pageTitles.append(uid)
}
}
self.pageViewController = self.storyboard?.instantiateViewControllerWithIdentifier("PageViewController") as! UIPageViewController
self.pageViewController.dataSource = self
let startVC = self.viewControllerAtIndex(0) as ContentViewController
let viewControllers = NSArray(object: startVC)
self.pageViewController.setViewControllers(viewControllers as? [UIViewController], direction: .Forward, animated: true, completion: nil)
self.pageViewController.view.frame = CGRectMake(0, 30, self.view.frame.width, self.view.frame.size.height - 60)
self.addChildViewController(self.pageViewController)
self.view.addSubview(self.pageViewController.view)
self.pageViewController.didMoveToParentViewController(self)
}
}