问题
The goal is to create a UIPageViewController that can only navigate forward. I am using a data source to provide the content for the UIPageViewController. The direction is set to UIPageViewControllerNavigationDirectionForward, the transition style is UIPageViewControllerTransitionStyleScroll.
The implementation of
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
// returns the next view controller
}
returns the next view controller, while the following should ensure navigating backwards is impossible
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
return nil;
}
Returning nil should indicate that navigation is not possible (as stated in the documentation). However, I am always possible to scroll back one page. Let's say I have 10 pages, I can scroll forward through all pages but at any page I can scroll back 1 page. (For example: at page 5 I can go back to page 4, at page 8 I can go back to page 7, and so on.)
I know I can avoid this by not using a data source and using the setViewControllers:direction:animated:completion: method, but I'd like to understand why my attempt is failing.
回答1:
This is the behavior you get when your pageViewController has its transition style set to scroll -- I'm not sure why, but it has something to do with a scroll view being inserted into the hierarchy somewhere (which I could see being allocated if I ran my project with Instruments turned on). If the transition is Page Curl, then you don't get any previous page being displayed if your return nil where you do.
So, I think you're stuck with using setViewControllers:direction:animated:completion: unless you want to switch to the Page Curl animation.
回答2:
Here is a simple solution, simply set isLeftScrollEnabled default value to false in the protocol: UIPageViewController with configurable scroll directions
来源：https://stackoverflow.com/questions/14426728/uipageviewcontroller-direction-only-forward