Question

I’m using UIPageViewController and story board in my application.
When in portrait, i’m using following code to jump from one page to another page and its working fine.

int direction = UIPageViewControllerNavigationDirectionForward;
if ([self.modelController currentPage] < pagenum)
{
    direction = UIPageViewControllerNavigationDirectionForward;
}
else if ([self.modelController currentPage] > pagenum)
{
    direction = UIPageViewControllerNavigationDirectionReverse;
}

[self.pageViewController setViewControllers:[NSArray arrayWithObject:[self.modelController viewControllerAtIndex:pagenum storyboard:self.storyboard]] direction:direction animated:YES completion:NULL];    

But the same code is not working when we are in landscape mode. How to turn the pages when in landscape?

Answer 1

If you look at the Page-Based Application Template in Xcode you find the following UIPageViewControllerDelegate method:

- (UIPageViewControllerSpineLocation)pageViewController:(UIPageViewController *)pageViewController spineLocationForInterfaceOrientation:(UIInterfaceOrientation)orientation
{
    if (UIInterfaceOrientationIsPortrait(orientation)) {
        // In portrait orientation: Set the spine position to "min" and the page view controller's view controllers array to contain just one view controller. Setting the spine position to 'UIPageViewControllerSpineLocationMid' in landscape orientation sets the doubleSided property to YES, so set it to NO here.
        UIViewController *currentViewController = [self.pageViewController.viewControllers objectAtIndex:0];
        NSArray *viewControllers = [NSArray arrayWithObject:currentViewController];
        [self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:NULL];

        self.pageViewController.doubleSided = NO;
        return UIPageViewControllerSpineLocationMin;
    }

    // In landscape orientation: Set set the spine location to "mid" and the page view controller's view controllers array to contain two view controllers. If the current page is even, set it to contain the current and next view controllers; if it is odd, set the array to contain the previous and current view controllers.
    DataViewController *currentViewController = [self.pageViewController.viewControllers objectAtIndex:0];
    NSArray *viewControllers = nil;

    NSUInteger indexOfCurrentViewController = [self.modelController indexOfViewController:currentViewController];
    if (indexOfCurrentViewController == 0 || indexOfCurrentViewController % 2 == 0) {
        UIViewController *nextViewController = [self.modelController pageViewController:self.pageViewController viewControllerAfterViewController:currentViewController];
        viewControllers = [NSArray arrayWithObjects:currentViewController, nextViewController, nil];
    } else {
        UIViewController *previousViewController = [self.modelController pageViewController:self.pageViewController viewControllerBeforeViewController:currentViewController];
        viewControllers = [NSArray arrayWithObjects:previousViewController, currentViewController, nil];
    }
    [self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:NULL];


    return UIPageViewControllerSpineLocationMid;
}

When returning UIPageViewControllerSpineLocationMid from the above method, you are telling the UIPageViewController that it should expect to display two UIViewControllers side by side (i.e. two pages).

The key here is that you must pass the correct number of UIViewControllers when calling the UIPageViewController’s setViewControllers:direction:animated:completion: method.

• Showing two pages? Pass two UIViewControllers.
• Showing one page? Pass one UIViewController.

---

The code you presented will never pass more than one UIViewController to the UIPageViewController.

If the UIPageViewControllerSpineLocation does not correspond with the amount of UIViewControllers you are passing it will crash or just do nothing.

Let me know if you need further help.