我从 Erica Sadun (https://github.com/erica/iOS-5-Cookbook) 那里偷了这个:
// Update interface to the given page
- (void) fetchControllersForPage: (uint) requestedPage orientation: (UIInterfaceOrientation) orientation
{
BOOL sideBySide = [self useSideBySide:orientation];
int numberOfPagesNeeded = sideBySide ? 2 : 1;
int currentCount = self.viewControllers.count;
uint leftPage = requestedPage;
if (sideBySide && (leftPage % 2)) leftPage--;
// Only check against current page when count is appropriate
if (currentCount && (currentCount == numberOfPagesNeeded))
{
if (pageNumber == requestedPage) return;
if (pageNumber == leftPage) return;
}
// Decide the prevailing direction by checking the new page against the old
UIPageViewControllerNavigationDirection direction = (requestedPage > pageNumber) ? UIPageViewControllerNavigationDirectionForward : UIPageViewControllerNavigationDirectionReverse;
[self updatePageTo:requestedPage];
// Update the controllers
NSMutableArray *pageControllers = [NSMutableArray array];
SAFE_ADD(pageControllers, [self controllerAtPage:leftPage]);
if (sideBySide)
SAFE_ADD(pageControllers, [self controllerAtPage:leftPage + 1]);
[self setViewControllers:pageControllers direction: direction animated:YES completion:nil];
}
// Entry point for external move request
- (void) moveToPage: (uint) requestedPage
{
[self fetchControllersForPage:requestedPage orientation:(UIInterfaceOrientation)[UIDevice currentDevice].orientation];
}
#pragma mark Delegate
- (UIPageViewControllerSpineLocation)pageViewController:(UIPageViewController *)pageViewController spineLocationForInterfaceOrientation:(UIInterfaceOrientation)orientation
{
NSUInteger indexOfCurrentViewController = 0;
if (self.viewControllers.count)
indexOfCurrentViewController = ((UIViewController *)[self.viewControllers objectAtIndex:0]).view.tag;
[self fetchControllersForPage:indexOfCurrentViewController orientation:orientation];
BOOL sideBySide = [self useSideBySide:orientation];
self.doubleSided = sideBySide;
UIPageViewControllerSpineLocation spineLocation = sideBySide ? UIPageViewControllerSpineLocationMid : UIPageViewControllerSpineLocationMin;
return spineLocation;
}
给她一点爱。并注意超级聪明的“if (sideBySide && (leftPage % 2)) leftPage--;”,它确保左页始终是奇数页。
-一个