我尝试在 UIPageViewController 中显示照片。首先，我在收藏 View 中显示我的照片，然后点击一张照片进入页面 View 。但是，当我在页面 View 中时，如果我滚动当前照片(向右或向左)，我发现 pageViewController:viewControllerBeforeViewController 和 pageViewController:viewControllerAfterViewController 方法将被调用(通过调用 NSLog 我找到了它)。

是否应该只调用一次这两个方法中的一个？我对此感到很困惑，并且在更新我的 photoNumber 以显示我想要的照片时遇到了很大的麻烦。

这是我的页面查看代码:

#import "PhotoPageViewController.h"
#import "PhotoViewController.h"

@interface PhotoPageViewController ()
@property (nonatomic)NSInteger previousPhotoNumber;
@end

@implementation PhotoPageViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.dataSource = self;
    self.delegate = self;

    self.numberOfPhotosInCurrentAlbum = [Photo numberOfPhotosInAlbumWithName:self.albumName inManagedObjectContext:self.context];
    PhotoViewController *currentPhotoViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"PhotoContentViewController"];
    currentPhotoViewController.photoNumber = self.currentPhotoNumber;
    currentPhotoViewController.albumName = self.albumName;
    currentPhotoViewController.context = self.context;

    currentPhotoViewController.ppvc = self;
    currentPhotoViewController.numberOfPhotosInCurrentAlbum =self.numberOfPhotosInCurrentAlbum;

    [self setViewControllers:@[currentPhotoViewController]
                   direction:UIPageViewControllerNavigationDirectionForward
                    animated:NO
                  completion:NULL];
}



#pragma mark - Page View Controller Datasource

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
    if (self.currentPhotoNumber > 0) {
        NSLog(@"in before section: current photo %lu", self.currentPhotoNumber);

        PhotoViewController *photoBeforeCurrentPhoto = [self.storyboard instantiateViewControllerWithIdentifier:@"PhotoContentViewController"];
        photoBeforeCurrentPhoto.photoNumber = self.currentPhotoNumber - 1;
        photoBeforeCurrentPhoto.albumName = self.albumName;
        photoBeforeCurrentPhoto.context = self.context;
        photoBeforeCurrentPhoto.ppvc = self;

        self.previousPhotoNumber = self.currentPhotoNumber;
        self.currentPhotoNumber--;

        return photoBeforeCurrentPhoto;
    }
    return nil;
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
    if (self.currentPhotoNumber < self.numberOfPhotosInCurrentAlbum - 1) {
        NSLog(@"in after section: current photo %lu", self.currentPhotoNumber);
        PhotoViewController *photoAfterCurrentPhoto = [self.storyboard instantiateViewControllerWithIdentifier:@"PhotoContentViewController"];
        photoAfterCurrentPhoto.photoNumber = self.currentPhotoNumber + 1;
        photoAfterCurrentPhoto.albumName = self.albumName;
        photoAfterCurrentPhoto.context = self.context;
        photoAfterCurrentPhoto.ppvc = self;

        self.previousPhotoNumber = self.currentPhotoNumber;
        self.currentPhotoNumber++;

        return photoAfterCurrentPhoto;
    }
    return nil;
}

PhotoViewController 是显示照片的 View Controller 。

谁能给我一些关于 UIPageViewController 用法的建议？

提前致谢!

最佳答案

UIPageViewController 使用下面这些方法获取前后 View Controller 。

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController;
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController;

虽然它很奇怪，但它是一个已知问题。每次调用 Before 和 After 方法来获取 VC。如果没有下一个 VC，则返回 nil，如果没有前一个 VC，datasourceDelegate 返回 nil，否则返回 VC 的索引。

在UIPageViewControllerDelegate中，有一个名为:

- (void)pageViewController:(UIPageViewController *)pageViewController willTransitionToViewControllers:(NSArray *)pendingViewControllers;

看看这个，它可能有助于从 pendingViewControllers 数组中获取当前或下一个/上一个 View Controller 。

希望这会有所帮助..:)

关于ios - 在 UIPageViewController 中，何时调用 "pageViewController:viewControllerBeforeViewController"？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22978879/