UIPageViewController, how do I correctly jump to a specific page without messing up the order specified by the data source?

I've found a few questions about how to make a UIPageViewController jump to a specific page, but I've noticed an added problem with jumping that none of the answers seem to acknowledge.

Without going into the details of my iOS app (which is similar to a paged calendar), here is what I'm experiencing. I declare a UIPageViewController, set the current view controller, and implement a data source.

// end of the init method
        pageViewController = [[UIPageViewController alloc] 
        initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll
          navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal
                        options:nil];
        pageViewController.dataSource = self;
        [self jumpToDay:0];
}

//...

- (void)jumpToDay:(NSInteger)day {
        UIViewController *controller = [self dequeuePreviousDayViewControllerWithDaysBack:day];
        [pageViewController setViewControllers:@[controller]
                                    direction:UIPageViewControllerNavigationDirectionForward
                                     animated:YES
                                   completion:nil];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController {
        NSInteger days = ((THDayViewController *)viewController).daysAgo;
        return [self dequeuePreviousDayViewControllerWithDaysBack:days + 1];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController {
        NSInteger days = ((THDayViewController *)viewController).daysAgo;
        return [self dequeuePreviousDayViewControllerWithDaysBack:days - 1];
}

- (UIViewController *)dequeuePreviousDayViewControllerWithDaysBack:(NSInteger)days {
        return [[THPreviousDayViewController alloc] initWithDaysAgo:days];
}

Edit Note: I added simplified code for the dequeuing method. Even with this blasphemous implementation I have the exact same problem with page order.

The initialization all works as expected. The incremental paging all works fine as well. The issue is that if I ever call jumpToDay again, the order gets jumbled.

If the user is on day -5 and jumps to day 1, a scroll to the left will reveal day -5 again instead of the appropriate day 0. This seems to have something to do with how UIPageViewController keeps references to nearby pages, but I can't find any reference to a method that would force it to refresh it's cache.

Any ideas?

Programming iOS6, by Matt Neuburg documents this exact problem, and I actually found that his solution feels a little better than the currently accepted answer. That solution, which works great, has a negative side effect of animating to the image before/after, and then jarringly replacing that page with the desired page. I felt like that was a weird user experience, and Matt's solution takes care of that.

__weak UIPageViewController* pvcw = pvc;
[pvc setViewControllers:@[page]
              direction:UIPageViewControllerNavigationDirectionForward
               animated:YES completion:^(BOOL finished) {
                   UIPageViewController* pvcs = pvcw;
                   if (!pvcs) return;
                   dispatch_async(dispatch_get_main_queue(), ^{
                       [pvcs setViewControllers:@[page]
                                  direction:UIPageViewControllerNavigationDirectionForward
                                   animated:NO completion:nil];
                   });
               }];

So I ran into the same problem as you where I needed to be able to 'jump' to a page and then found the 'order messed up' when I gestured back a page. As far as I have been able to tell, the page view controller is definitely caching the view controllers and when you 'jump' to a page you have to specify the direction: forward or reverse. It then assumes that the new view controller is a 'neighbor' to the previous view controller and hence automagically presents the previous view controller when you gesture back. I found that this only happens when you are using the UIPageViewControllerTransitionStyleScroll and not UIPageViewControllerTransitionStylePageCurl. The page curl style apparently does not do the same caching since if you 'jump' to a page and then gesture back it delivers the pageViewController:viewController(Before/After)ViewController: message to the data source enabling you to provide the correct neighbor view controller.

Solution: When performing a 'jump' to page you can first jump to the neighbor page to the page (animated:NO) you are jumping to and then in the completion block of that jump, jump to the desired page. This will update the cache such that when you gesture back, the correct neighbor page will be displayed. The downside is that you will need to create two view controllers; the one you are jumping to and the one that should be displayed after gesturing back.

Here is the code to a category that I wrote for UIPageViewController:

@implementation UIPageViewController (Additions)

 - (void)setViewControllers:(NSArray *)viewControllers direction:(UIPageViewControllerNavigationDirection)direction invalidateCache:(BOOL)invalidateCache animated:(BOOL)animated completion:(void (^)(BOOL finished))completion {
	NSArray *vcs = viewControllers;
	__weak UIPageViewController *mySelf = self;
	
	if (invalidateCache && self.transitionStyle == UIPageViewControllerTransitionStyleScroll) {
		UIViewController *neighborViewController = (direction == UIPageViewControllerNavigationDirectionForward
													? [self.dataSource pageViewController:self viewControllerBeforeViewController:viewControllers[0]]
													: [self.dataSource pageViewController:self viewControllerAfterViewController:viewControllers[0]]);
		[self setViewControllers:@[neighborViewController] direction:direction animated:NO completion:^(BOOL finished) {
			[mySelf setViewControllers:vcs direction:direction animated:animated completion:completion];
		}];
	}
	else {
		[mySelf setViewControllers:vcs direction:direction animated:animated completion:completion];
	}
}

@end

What you can do to test this is create a new 'Page-Based Application' and add a 'goto' button that will 'jump' to a certain calendar month and then gesture back. Be sure to set the transition style to scroll.

I use this function (I'm always in landscape, 2 page mode)

-(void) flipToPage:(NSString * )index {


int x = [index intValue];
LeafletPageContentViewController *theCurrentViewController = [self.pageViewController.viewControllers   objectAtIndex:0];

NSUInteger retreivedIndex = [self indexOfViewController:theCurrentViewController];

LeafletPageContentViewController *firstViewController = [self viewControllerAtIndex:x];
LeafletPageContentViewController *secondViewController = [self viewControllerAtIndex:x+1 ];


NSArray *viewControllers = nil;

viewControllers = [NSArray arrayWithObjects:firstViewController, secondViewController, nil];


if (retreivedIndex < x){

    [self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:NULL];

} else {

    if (retreivedIndex > x ){

        [self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionReverse animated:YES completion:NULL];
      } 
    }
} 

Here is my Swift solution to be used for subclasses of UIPageViewController:

Assume you store an array of viewControllers in viewControllerArray and the current page index in updateCurrentPageIndex.

  private func slideToPage(index: Int, completion: (() -> Void)?) {
    let tempIndex = currentPageIndex
    if currentPageIndex < index {
      for var i = tempIndex+1; i <= index; i++ {
        self.setViewControllers([viewControllerArray[i]], direction: UIPageViewControllerNavigationDirection.Forward, animated: true, completion: {[weak self] (complete: Bool) -> Void in
          if (complete) {
            self?.updateCurrentPageIndex(i-1)
            completion?()
          }
          })
      }
    }
    else if currentPageIndex > index {
      for var i = tempIndex - 1; i >= index; i-- {
        self.setViewControllers([viewControllerArray[i]], direction: UIPageViewControllerNavigationDirection.Reverse, animated: true, completion: {[weak self] (complete: Bool) -> Void in
          if complete {
            self?.updateCurrentPageIndex(i+1)
            completion?()
          }
          })
      }
    }
  }

Swift version of djibouti33's answer:

weak var pvcw = pageViewController
pageViewController!.setViewControllers([page], direction: UIPageViewControllerNavigationDirection.Forward, animated: true) { _ in
        if let pvcs = pvcw {
            dispatch_async(dispatch_get_main_queue(), {
                pvcs.setViewControllers([page], direction: UIPageViewControllerNavigationDirection.Forward, animated: false, completion: nil)
            })
        }
    }

It's important to note that this is no longer the case in iOS 10 and you no longer have to use the accepted answer solution. Just continue as always.

I can confirm this issue, and that it only happens when using UIPageViewControllerTransitionStyleScroll and not UIPageViewControllerTransitionStylePageCurl.

Workaround: Make a loop and call UIPageViewController setViewControllers for each page turn, until you reach the desired page.

This keeps the internal datasource index in UIPageViewController in sync.

This is only solution

-(void)buyAction
{
    isFromBuy = YES;
    APPChildViewController *initialViewController = [self viewControllerAtIndex:4];
    viewControllers = [NSArray arrayWithObject:initialViewController];
    [self.pageController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];
}

-(NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController 
{
    if (isFromBuy) {
        isFromBuy = NO;
        return 5;
    }
    return 0;
}

I had a different approach, should be possible if your pages are designed to be updated after init:
When a manual page is selected I update a flag

- (void)scrollToPage:(NSInteger)page animated:(BOOL)animated
{
    if (page != self.currentPage) {
        [self setViewControllers:@[[self viewControllerForPage:page]]
                       direction:(page > self.currentPage ?
                                  UIPageViewControllerNavigationDirectionForward :
                                  UIPageViewControllerNavigationDirectionReverse)
                        animated:animated
                      completion:nil];
        self.currentPage = page;
        self.forceReloadNextPage = YES; // to override view controller automatic page cache
    }
}

- (ScheduleViewController *)viewControllerForPage:(NSInteger)page
{
    CustomViewController * scheduleViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"CustomViewController"];
    scheduleViewController.view.tag = page; // keep track of pages using view.tag property
    scheduleViewController.data = [self dataForPage:page];

    if (self.currentViewController)
        scheduleViewController.calendarLayoutHourHeight = self.currentViewController.calendarLayoutHourHeight;

    return scheduleViewController;
}

and then force the the next page to reload with the correct data:

- (void)pageViewController:(UIPageViewController *)pageViewController willTransitionToViewControllers:(NSArray *)pendingViewControllers
{
    CustomViewController * nextViewController = [pendingViewControllers lastObject];

    // When manual scrolling occurs, the next page is loaded from UIPageViewController cache
    //  and must be refreshed
    if (self.forceReloadNextPage) {
        // calculate the direction of the scroll to know if to load next or previous page
        NSUInteger page = self.currentPage + 1;
        if (self.currentPage > nextViewController.view.tag) page = self.currentPage - 1;

        nextViewController.data = [self dataForPage:page];
        self.forceReloadNextPage = NO;
    }
}

If you do not need to animate to the new page, as I didn't, the following code worked for me, called on "Value Changed" in the storyboard. Instead of changing between view controllers, I change the data associated with the current view controller.

    - (IBAction)pageControlCurrentPageDidChange:(id)sender
{
    self.currentIndex = self.pageControl.currentPage;
    MYViewController *currentPageViewController = (MYViewController *)self.pageViewController.viewControllers.firstObject;
    currentPageViewController.pageData = [self.pageDataSource dataForPage:self.currentIndex];
    [currentPageViewController updateDisplay];
}

currentIndex is there so I can update the pageControl's currentPage when I swipe between pages.

pageDataSource dataForPage: returns an array of data objects that are displayed by the pages.

Here is an up-to-date Swift 3+ version of the answer by @djibouti33 with cleaned-up syntax.

weak var weakPageVc = pageVc

pageVc.setViewControllers([page], direction: .forward, animated: true) { finished in
    guard let pageVc = weakPageVc else {
        return
    }
    
    DispatchQueue.main.async {
        pageVc.setViewControllers([page], direction: .forward, animated: false)
    }
}

    let orderedViewControllers = [UIViewController(),UIViewController(), UIViewController()]
    let pageViewController = UIPageViewController()
    let pageControl = UIPageControl()
    
    func jump(to: Int, completion: @escaping (_ vc: UIViewController?) -> Void){
        
        guard orderedViewControllers.count > to else{
            //index of bounds
            return
        }
        
        let toVC = orderedViewControllers[to]
        
        var direction: UIPageViewController.NavigationDirection = .forward
        
        if pageControl.currentPage < to {
            direction = .forward;
        } else {
            direction = .reverse;
        }
        
        pageViewController.setViewControllers([toVC], direction: direction, animated: true) { _ in
            DispatchQueue.main.async {
                self.pageViewController.setViewControllers([toVC], direction: direction, animated: false){ _ in
                    self.pageControl.currentPage = to
                        completion(toVC)
                    
                }
            }
        }
    }

USAGE:

self.jump(to: 5) { (vc) in
    // you can do anything for new vc.
}

I was struggling with this issue for a long time myself. For me I had a UIPageViewController (I called it PageController) load from storyboard and on it I add a UIViewController 'ContentVC'.

I let the ContentVC takes care of the data to be loaded on to the content area and let PageController takes care of the sliding/goto/PageIndicator updates. The ContentVC has an ivar CurrentPageIndex and sends that value to PageController so PageController knows which page it's on. In my .m file that has PageController I have these two methods.

Note that I used set to 0 and so every time PageVC reloads it goes to the first page which I don't want, [self viewControllerAtIndex:0].

- (void)setPageForward
{  
  ContentVC *FirstVC = [self viewControllerAtIndex:[CurrentPageIndex integerValue]];

  NSArray *viewControllers = @[FirstVC];
  [PageController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];
}

This second method is PageViewController's DataSource method. presentationIndexForPageViewController will set the highlighted dot to the right page (the page you want). Note that if we return 0 here the page indicator will highlight the first dot which indicates the first page and we don't want that.

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController 
{
  return [CurrentPageIndex integerValue];
}