📖 A simple, highly informative page view controller

@msaps We have 14 apps that are using pageboy as a dependency of Tabman and when we swipe about 10 pages fast after each other the app crashes with an Assertion failure. From the stacktrace we get an Assertion failure in Pageboy without any further specifications. We have a big userbase and it is currently causing a lot of crashes so a quick fix would be very helpful for us!

Our stacktrace: ` 2022-10-28 11:33:14.353745+0200 Groei[58716:22674120] *** Assertion failure in -[Pageboy.PatchedPageViewController queuingScrollView:didEndManualScroll:toRevealView:direction:animated:didFinish:didComplete:], UIPageViewController.m:2040

2022-10-28 11:33:14.357491+0200 Groei[58716:22674120] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'No view controller managing visible view <UIView: 0x131686a70; frame = (0 0; 390 844); autoresize = W+H; backgroundColor = <UIDynamicCatalogColor: 0x282618320; name = Primary/Background>; layer = <CALayer: 0x28013e460>>'

*** First throw call stack: (0x1affea248 0x1a93afa68 0x1aa96e81c 0x1b290014c 0x1b290a164 0x1b290ba9c 0x1b290926c 0x1b290a35c 0x1b28fde3c 0x1b28fe000 0x10592ba20 0x10592bef4 0x10592549c 0x105925194 0x1059246e8 0x105924ad0 0x100d482ac 0x100d48a40 0x100d4a97c 0x100d4ad30 0x10950a048 0x10950a8ac 0x1094b8a34 0x10950cdb4 0x10950cfac 0x10952d880 0x109532874 0x109533fd8 0x109532954 0x10950bcfc 0x10950c7b8 0x1094fca2c 0x10950bfd8 0x10950cdb4 0x10950cfac 0x10952d880 0x1094df5b0 0x1094df640 0x1094b900c 0x1094b8c78 0x10952a0e4 0x100ad84e8 0x100ad88e4 0x101b2584c 0x1019ffd74 0x1019dd364 0x1019ff498 0x1019436a0 0x100ad8114 0x100ad7dec 0x100ad7f48 0x100ec82cc 0x101b2584c 0x1019ffd74 0x1019dd364 0x101b9e71c 0x101bc7ad4 0x101b9e2f0 0x101b50a84 0x101b510f8 0x101b5133c 0x101b4fcc8 0x101b72cdc 0x101b6275c 0x101b6230c 0x101b6a014 0x101b69938 0x101b71440 0x101c3c140 0x101be9130 0x101c42e10 0x101bf108c 0x101bf1144 0x101bf1250 0x101b72980 0x101b637d8 0x101b6296c 0x101b60d30 0x101b6a5f4 0x101b69fd8 0x101b69bc4 0x101b46794 0x1019dd638 0x101b9e664 0x101b9e9b8 0x101b9e28c 0x101b50a84 0x101b51e78 0x101b84bf0 0x101b79b58 0x101b789b8 0x101b8d2a4 0x101e071a8 0x101e099ec 0x1b1174968 0x1069a0598 0x1069a204c 0x1069b2800 0x1069b2344 0x1b007aa08 0x1b005c368 0x1b00611e4 0x1e8e81368 0x1b2510d88 0x1b25109ec 0x100af1780 0x1ce385948)

libc++abi: terminating with uncaught exception of type NSException

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'No view controller managing visible view <UIView: 0x131686a70; frame = (0 0; 390 844); autoresize = W+H; backgroundColor = <UIDynamicCatalogColor: 0x282618320; name = Primary/Background>; layer = <CALayer: 0x28013e460>>' terminating with uncaught exception of type NSException `

When anything more is needed you can let us know.

If push a VC when the auto-scroll transition start, when back to the PageBoyVC, it will not respond to scroll/tap and autoScroller stop working too.

This is only happen with autoScroller. It's working fine with user-scroll

Hey @msaps This is a freak issue in that it just appeared out of nowhere but Im hoping you can give me hints.

So basically my ViewHierachy is like this

-> ParentViewController 
----> PageboyViewController (Child of Parent)
----------> LeftVC
----------> MainVC

It appears my PageboyVC's childControllers (LeftVC & MainVC) does not extend to the bottom of the screen on an iPhone X. Ive had instances where it was working fine but the issue recently reappeared without me able to retrace what exactly I could have done to cause it(up to now i can't pinpoint)

Any hints? I haven't been able to recreate it with your example project but will try it out tomorrow.

Thanks

Hello! Thanks for a great tool!

When doing a memory leak audit I found one inside your Pod.

I believe the fix is to use [weak self] on lines 71 and 76 of PageboyViewController+Management.swift

Here's a screenshot from xcode showing the leak:

https://imgur.com/a/V5mprcD

@msaps Hi man Here I am again 😊 😁 I found another issue that is critical in my opinion. The "Tabman" or "Pageboy", I do not know exactly. However, you use some strong reference cause appear this issue.

For Simulate what happened to me. Please Use NavigationController as application rootViewController then push object which inherits from "Tabman" library. After that back to rootViewController of NavigationController. The "Tabman" or "Pageboy" must be deallocated after pop TabmanViewController or PageboyViewController but never called deinit Note: declare deinit function in "Tabman" or "Pageboy" or A class inherit from both deinit{ print("\(self)") print self for debug log of the memory address.

I've recently started coding again after quite some time off due to studying a lot. But somehow my app's been crashing pretty often due to memory issues and naturally, I tried to find the cause, e.g. a retain cycle - in my own code. However, even after hours of searching and trying to strip my code down to the very basics I just couldn't get rid of the leak. And when debugging the memory graph I noticed something odd: The number of pages, i.e. SubViewControllers of my PageboyViewController, was way too high. Although I had in total 6 pages it displayed a bunch more (e.g. 21) when I debugged it. I noticed I could induce the problem by going back and forth a lot (e.g. from page 1 to 6 and back) and indeed I could watch my memory go up in the memory leak-typical manner with virtually every new page. The problem wouldn't occur, though if I didn't go back and forth.

To make sure it wasn't because of my code I first replaced the old pages with other, simpler ViewControllers but it still wasn't going away. The app still crashed although it did seem to take a little longer. The videos in my usual pages seemed to add to the problem.

Anyways, now I created a simple project with a normal UIPageViewController and a PageBoyViewController to compare them. I'm using Pageboy (3.0.5) (from Podefile.lock) and also installed a simple video player pod (Player) so that the pages in the controller would resemble my project to some extent.

In my example project, I used exactly 10 pages which always showed the same video. As you can see on the left of the picture (debugged memory graphs), 21 instances of VideoPlayer (my SubViewController of the respective PageViewController) were created when I used PageBoy. On the contrary, only 10 (the total number of SubViewControllers) were created when I used a "normal" (therefore NormalViewController) UIPageViewController.
To be able to compare them I tried to induce the crash as described above in both controllers. When I noticed the former (PageBoyController) became slower, I debugged. If I don't stop, however, it will invariably crash with Message from debugger: Terminated due to memory issue. Trying to induce the crash the same way in the "normal" UIPageViewController didn't work (even after one entire minute of rapidly going back and forth).

If you would like me to share my example project, please let me know.

Now the bad news: Unfortunately, I couldn't find the cause. I've analyzed the debugged memory graph a lot but couldn't find e.g. a retain cycle. I have to admit, though, that I am not very experienced at this, too. Therefore, I would really appreciate if someone could help me with this problem. I really like the pod and wouldn't wanna work without it but this is a little too hard of a problem for me (as no CS student) to solve. Thank you!

PS: Please let me know if there are any questions or if anything remains unclear. I'll try to provide answers as precisely as possible.

Hi!

Sorry for my bad english... I have found a bug when I do a second swipe and the first is not finished :

• The background color is blue and not orange
• The Current Position and Current Page are 0.0, not 1.0
• "Previous" button is disabled
• Text is good (Page 2) for the first test but nothing appear for the second test

The screen record :

Thanks for your help

PageViewController display ViewController as full screen. Therefore, Next or Previous ViewController should not be initialized when they before displaying.

But, Current DataSource APIs require all ViewControllers.

 func viewControllers(forPageboyViewController pageboyViewController: PageboyViewController) -> [UIViewController]?

I think that add below API likes UICollectionViewDataSource. Example,

 func viewController(forPageboyViewController pageboyViewController: PageboyViewController, at index: Int) -> UIViewController

This API improves initialize performance when PageBoy has many viewControllers.

What do you think?

@msaps Is there any plan to support pages on top or below? Im looking to create a 3 page view [Left, Center, Top] where Top is above Left.

Also side question didnt want to raise issue but can bounce be disabled on First and Last page?

Hi,

so, let's say we have a PageboyViewController that is set up with 1 page. Then I am updating my input for the PageboyViewControllerDataSource and calling insertPage(at: 0, then: .doNothing).

What I would expect is that the new page will be inserted right before my current ViewController but I'm staying at the current ViewController, because I've specified .doNothing as PageUpdateBehavior.

What happens is that the new page is indeed inserted before my current ViewController, but also it "cross-dissolves" to the inserted ViewController.

I see that this is implemented in the func performUpdates when it's checked if newIndex == currentIndex and then the crossDissolve + updateViewControllers is done. I guess that totally makes sense for deleting the page at the currentIndex, but I'm not sure if this is the desired behaviour for inserting?

Thanks in advance! (And thanks for building/improving this great library 👍 )

Version

Pageboy (3.2.0) (actually used with Tabman (2.3.0) but this should be just related to Pageboy)

@msaps Is it possible to have navigation bar items and titles transition in the manner shown below (Either with Pageboy or Tabman)? It makes for a very simple & intuitive navigation scheme in my opinion.

func pageboyViewController(_ pageboyViewController: PageboyViewController, didScrollTo position: CGPoint, direction: PageboyViewController.NavigationDirection, animated: Bool)

This delegate method does not fire

When isInfiniteScrollEnabled is true and the scroll direction changes on the last page, the view controller disappears intermittently. This is easy to reproduce if you have two viewcontrollers.

Here is my code

import UIKit
import Pageboy

class ViewController: PageboyViewController {
    let firstVC: UIViewController = {
        let viewController = UIViewController()
        viewController.view.backgroundColor = .systemOrange
        return viewController
    }()
    
    let secondVC: UIViewController = {
        let viewController = UIViewController()
        viewController.view.backgroundColor = .systemPurple
        return viewController
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.dataSource = self
        self.isInfiniteScrollEnabled = true
    }
}

extension ViewController: PageboyViewControllerDataSource {
    func numberOfViewControllers(in pageboyViewController: PageboyViewController) -> Int {
        2
    }
    
    func viewController(for pageboyViewController: PageboyViewController, at index: PageboyViewController.PageIndex) -> UIViewController? {
        switch index {
        case 0:
            return firstVC
        case 1:
            return secondVC
        default:
            fatalError("unknown index!")
        }
    }
    
    func defaultPage(for pageboyViewController: PageboyViewController) -> PageboyViewController.Page? {
        .first
    }
}

Issue: I have a PageBoyViewController set up to handle 2 other view controllers. From a different controller I am trying to navigate to the second viewController of the PageBoyViewController. When I navigate to the PageBoyViewController and switch indexes on viewWillAppear it go passed the intended index. Also, this issue only seems to appear on an iPhone 8 which is running version 12.4.

To Replicate:

• Have a PageBoyViewController as a tab on a tabBarController.
• On the PageBoyViewController, navigate to the first index
• Navigate to a different ViewController
• From that ViewController switch to the PageBoyViewController
• In the viewWillAppear of the PageBoyViewController navigate to the second index

Hello~ thank you for developing Pageboy open source🙂

i wanna modify the currentIndex while using the Pageboy. can you modify the updateCurrentPageIndexIfNeeded located in the internal class that it can be used in an external project? The reason for modifying the currentIndex is that when a datasource is updated as new one, the currentIndex is changed to 0, which is why scrollToPage is not being used as my intended.

for example, current tab index is 3 -> update tab -> currentIndex is changed to 0

I wanna keep currentIndex as 3. that's the reason why I wanna modify updateCurrentPageIndexIfNeeded function!

of course if you have other solutions, please let me know🙏🏼

thank you and have a nice day~!