I have difficulties to scroll programatically my UIPageViewController embedded in a main UIViewController, here is the architecture of my screen :
At the bottom of my screen I’m using UIPageViewController to display 2 controllers.
At the top of my screen I have a UICollectionView which is not part of the pageViewController.
For some needs, I synchronized the scroll of the collectionView with the scroll of the pagerViewController.
So now I have a pagerViewController that is scrolling when user scrolls into my collectionView. I’m using : pagerScrollView.setContentOffset(CGPoint(...) to do that.
My problem is that UIPageViewController uses its gestureRecognizers property to call its datasource methods properly. But when playing with pagerScrollView.setContentOffset, its dataSource methods are not called, so the next controller is not provided.
These are not called :
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController?
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
I tried to call pagerController.setViewControllers in the scrollViewWillBeginDragging method, but the controller is immediately changed, the UIPageViewController don’t keep the controller that is being transitionned.
My question is the following :
Is there a way to tell the UIPageViewController which controller is next / before without losing the controller that is currently transitioned ? Or is there a way to fire datasource methods using the setContentOffset method on my pager ?
When scrolling into the pagerViewController, obviously everything is working well because its datasource methods are called.
Any idea?
Related
There are many SO questions talk about preload but seems none of them discuss how to do this during initialize.
I want to preload the next page when UIPageViewController is initialized.
For example, I initial UIPageViewController with the following code.
// [firstVC, secondVC]
setViewControllers([firstVC], direction: .forward, animated: true)
Unfortunately, datasource delegate function won't be called at the moment.
They will be called when user interaction involve.
In another word, when user swipe page.
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController?
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController?
I tried to "scroll" view programmatically.
It shows blank, there is nothing on the scrollView at the region.
// self is a UIPageViewController
if let scrollView = self.view.subviews.first(where: { $0 is UIScrollView }) as? UIScrollView {
var offset = scrollView.contentOffset
offset.x += 200
scrollView.setContentOffset(offset, animated: true)
}
Also tried to set 2 viewControllers when initialize but app crash.
setViewControllers([firstVC, secondVC], direction: .forward, animated: true)
Can I preload without user interaction?
Update.
So when user open the pageVC, I want to do a small swipe to user to demo this new feature, like the left image, since user doesn't know they can swipe so no user interaction at the moment.
If I can't preload the next view, it will look like the right image (white means nothing in this sample), empty view will make user confused, they could think this is a bug.
Update:
Github
I need to show some media contents on UIPageViewController and allow user to swipe between medias (just like a gallery) and I do not know how many videos or images are ahead because I have to get them one by one from server. How can I use UIPageViewController with unknown page numbers and just knowing previous and next page view controller?
You can try using Collection view like a page view controller. You can try making the collection view cell to fit the screen like a page view controller and Update the data source and collection view as and when required.
You can see a sample here in HomeViewController
For UIPageViewController you do not need to provide total number of items to make it works. When setting up your UIPageViewController, you only need to set the View Controller you want to display when it first loaded by following code:
pageViewController.setViewControllers([viewControllerToBeDisplayed], direction: .forward, animated: false, completion: nil)
And then to enable user to go back and forth, you just need to implement following methods of UIPageViewControllerDataSource:
public func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController?
public func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController?
Hope it helps.
Problem: UIPageViewController navigation between pages works fine but:
1) Navigation dots view not showing up
2) Some dataSource methods not called (probably cause for 1.)
I have following UI setup (basically UIPageViewController in UITableViewCell)
UITableViewCell <- UIViewController <- ContainerView <- UIPageViewController
Problem:
CALLED OK:
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController?
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController?
NOT CALLED:
func presentationCount(for pageViewController: UIPageViewController) -> Int
func presentationIndex(for pageViewController: UIPageViewController) -> Int
All setup done after viewDidLoad:
dataSource = self
setViewControllers([viewController], direction: .reverse, animated: false, completion: nil)
Note: I'm using another UIPageViewController somewhere else in the app directly on the content view -> there all delegate methods are working fine. Another (probably directly related) problem is that navigation dot view is not visible. (Again works fine in case where not embedded).
Anybody experience anything like this?
Why would some dataSource delegate methods be called while others would not called?
I've been looking at this code and all I could find in google for hours but can't move forward.
UIPageViewController Implementation
A page indicator will be visible if both methods are implemented, transition style is 'UIPageViewControllerTransitionStyleScroll', and navigation orientation is 'UIPageViewControllerNavigationOrientationHorizontal'.
Both methods are called in response to a 'setViewControllers:...' call, but the presentation index is updated automatically in the case of gesture-driven navigation.
According to Apple Documentation you need to implement both methods and make sure that the controller's transition style is "scroll". Then the Page Indicator will be visible and the functions are called. Please check this.
for the visibility of the pageindicator. Add below code in viewdidload
var pageControl = UIPageControl.appearance()
pageControl.pageIndicatorTintColor = UIColor.lightGray
pageControl.currentPageIndicatorTintColor = UIColor.white
pageControl.backgroundColor = UIColor.black
func presentationCount(for pageViewController: UIPageViewController) -> Int {
return orderedViewControllers.count
}
func presentationIndex(for pageViewController: UIPageViewController) -> Int {
if let currentVC = self.viewControllers!.first {
let currentIndex = orderedViewControllers.index(of: currentVC)
return currentIndex!
}else{
return 0
}
}
According to Apple Documentation you need to implement both methods and make sure that the controller's transition style is "scroll". Then the Page Indicator will be visible and the functions are called. Please check this.
Actually Vishal stated this, but not very clear :)
So I'm working on an App right now and one of the specs of this app is to have a swipe between views functionality on specific pages kind of like the camera on Instagram.
My current solution is to set the initial view controller as a UIPageViewController which has two view controllers one is the main tab bar controller (first image) for the whole app and the second view controller is the one shown in pink in the image above, and then to enable and disable sliding functionality for the PageViewController depending on whether the current view is meant to have access to the second 'pink' view controller. (PS open to a totally different architecture than this if anyone knows of one, this is just the best I could do given my limited knowledge on iOS)
Normally every thing works fine. However, when I move my finger's in a very particular pattern, the entire app stops functioning. The pattern is shown below:
The pattern is basically:
Swipe slowly to the left a little bit until part of the second 'pink' view controller is showing (image 2 above)
Swipe quickly to the right causing the empty space to the left of the main view controller to show (image 3)
Quickly Let go and let the main view controller fall back into place (image 4)
(*edit - Probably worth noting that if I do this same pattern slowly instead of quickly sliding right and letting go everything works just fine)
(PS if there's a way to upload a screen recording let me know)
Anyways, If I do this just one time, my entire app stops working. Basically every page stops loading data, and any time I click on a button on the main page (eg. the likes button shown in the images) I get an "Unbalanced calls to begin/end appearance transitions for AppName.ViewController" and the new view controller shows up with no data.
Furthermore, as soon as I swipe over to the second page 'pink' view controller and then back to the main app, everything works again.
I don't really know what code is relevant to this problem (spent about 5 hours trying to figure that out with no luck), so I'm just gonna post my UIPageViewController class for now, if you think the problem is coming from somewhere else let me know and I'll post that code.
// MARK: -> Properties
class PageViewController: UIPageViewController {
var pages = [UIViewController]()
}
// MARK: -> Lifecycle
extension PageViewController {
override func viewDidLoad() {
super.viewDidLoad()
self.dataSource = self
setViewController(withIdentifier: "MainTabController")
setViewController(withIdentifier: "SecondaryPage") // The 'Pink' screen
setViewControllers([pages.first!], direction: UIPageViewControllerNavigationDirection.forward, animated: false, completion: nil)
}
}
// MARK: -> Helpers
fileprivate extension PageViewController {
func setViewController(withIdentifier storyboardIdentifier: String){
let page: UIViewController! = storyboard?.instantiateViewController(withIdentifier: storyboardIdentifier)
storyboard?.configure(viewController: page)
self.pages.append(page)
}
}
// MARK: -> UIPageController Data Source
extension PageViewController: UIPageViewControllerDataSource {
func presentationIndex(for pageViewController: UIPageViewController)-> Int {
return pages.count
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
let cur = pages.index(of: viewController)!
if cur == 0 { return nil }
let prev = abs((cur - 1) % pages.count)
return pages[prev]
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
let cur = pages.index(of: viewController)!
if cur == (pages.count - 1) { return nil }
let nxt = abs((cur + 1) % pages.count)
return pages[nxt]
}
}
Update
Not sure what exactly this means but I'm sure it's relevant. I added this extension and method to my PageViewController
extension PageViewController: UIPageViewControllerDelegate {
func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
print(completed)
}
}
(and then obviously set the delegate to self in viewDidLoad)
This printed true and false as you would expect except when I swiped in the pattern I described above, in which case it never even fired the method and printed nothing at all.
I have a viewcontroller (FirstVC.swift) with a container view, in the upper part, that has an embedded pageviewcontroller (SecondPageVC.swift), and a view that has 3 buttons in the lower part.
At first, the only button visible is the middle button and other two is hidden. If the user reaches the last page, the other two buttons should appear. How do I pass the bool value that will make the buttons appear?
In my SecondPageVC.swift
func pageViewController(pageViewController: UIPageViewController,
viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
if index == myViewControllers.count-1{ //if last page
hide = true
}
Define a protocol called PageDelegate like this :
protocol PageDelegate { func hasReachLastPage(hasReached: Bool) }
Create a delegate var in your SecondPageVC like this : weak var delegate: PageDelegate?
On your pageViewController func called your func hasReachLastPage(hasReached: Bool) like this :
func pageViewController(pageViewController: UIPageViewController,
viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
if index == myViewControllers.count-1{ //if last page
delegate?.hasReachLastPage(true)
}
On your FirstVC makes it adopt your protocol that you just create like this : FirstVC : PageDelegate
Then, on your FirstVC when you have an instance of your SecondPageVC you are going to set your delegate variable to that FirstVC like this : SecondPageVC.delegate = self
You are saying that FirstVC is going to handle SecondPageVC delegate methods
Finally always on your FirstVC you have to implement the body of func hasReachLastPage(hasReached: Bool) by hidding or not your two buttons like this :
func hasReachLastPage(hasReached: Bool) {
if hasReached {
// Unhide two buttons
} else {
// Hide buttons or whatever
}
}
This is how you implement the delegate pattern. It's something very used and very useful to pass data between view controllers.
So, if I understand correctly, you just want to pass this hide property to the instance of FirstVC? If so, I would advise you to define a protocol SecondPageVCDelegate with a method secondPageVCDidReachLastPage:. Assigning the delegate can be done in prepare for segue method of the FirstVC.