Ios UIPageViewController的行为与Scroll&；不同；页面卷曲

我看到

UIPageViewController

使用

Scroll

转换与

PageCurl

之间的行为有所不同。PageCurl的工作方式与我预期的相同，但在使用滚动时，我有时会看到对

ViewControllerBeforReviewController:

和

viewControllerAfterViewController:

有人知道这种额外数据源调用的模式吗

我正在显示一系列图像，我可以从序列中的任何位置开始。 当使用滚动转换（而不是PageCurl）时，如果我移动到“右侧”，则在显示初始页面后，我会收到3个数据源调用，而不是我预期的单个调用。对于下面的示例，我从索引值3开始。当我滑动移动到“下一个”图像时，我希望得到一个

viewControllerAfterViewController:

调用索引3以访问索引4。如果我运行一个测试，我会得到两个额外的调用：一个用于索引3之前（即2），一个用于索引4之后（即5）。输出为：

2013-04-19 12:37:33.964 Clouds[496:907] Page 3 - viewControllerAfterViewController called on this index
2013-04-19 12:37:33.988 Clouds[496:907] Page 3 - viewControllerBeforeViewController called on this index
2013-04-19 12:37:34.010 Clouds[496:907] willTransitionToViewControllers to indices
2013-04-19 12:37:34.014 Clouds[496:907] Page 4
2013-04-19 12:37:34.461 Clouds[496:907] Page 4 - viewControllerAfterViewController called on this index

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.pageViewController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil];
    self.pageViewController.delegate = self;
    self.pageViewController.dataSource = self;


    CloudImageVC *startingViewController = [self viewControllerAtIndex:self.currentPage storyboard:self.storyboard];
    NSArray *viewControllers = @[startingViewController];
    [self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:NULL];

    [self addChildViewController:self.pageViewController];
    [self.view addSubview:self.pageViewController.view];

    CGRect pageViewRect = self.view.bounds;
    self.pageViewController.view.frame = pageViewRect;

    [self.pageViewController didMoveToParentViewController:self];

    // Add the page view controller's gesture recognizers to the book view controller's view so that the gestures are started more easily.
    self.view.gestureRecognizers = self.pageViewController.gestureRecognizers;
}

- (CloudImageVC *)viewControllerAtIndex:(NSUInteger)index storyboard:(UIStoryboard *)storyboard {
    // Return the data view controller for the given index.
    if (index >= [self.imageNames count]) {
        return nil;
    }
    self.dataViewController = [self makeDataViewControllerAtIndex:index storyboard:storyboard];
    return self.dataViewController;
 }

- (CloudImageVC *) makeDataViewControllerAtIndex:(NSUInteger)index storyboard:(UIStoryboard *)storyboard {
    // Make and return the data view controller for the given index.
    if (index >= [self.imageNames count]) {
        return nil;
    }
    // Create a new view controller and pass suitable data.
    self.dataViewController = [storyboard instantiateViewControllerWithIdentifier:@"CloudImageVC"];
    self.dataViewController.imageIndex = index;
    //self.dataViewController.cloudImage = nil;
    return self.dataViewController;
}

- (NSUInteger)indexOfViewController:(CloudImageVC *)viewController
{
    // Return the index of the given data view controller.
    // For simplicity, we store the index value in the view controller.
    return viewController.imageIndex;
}

#pragma mark - Page View Controller Data Source

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController {
    NSUInteger index = [self indexOfViewController:(CloudImageVC *)viewController];
    NSLog(@"Page %d - viewControllerBeforeViewController called on this index", index);
    if ((index == 0) || (index == NSNotFound)) {
        return nil;
    }
    index--;
    return [self viewControllerAtIndex:index storyboard:viewController.storyboard];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController {
    NSUInteger index = [self indexOfViewController:(CloudImageVC *)viewController];
    NSLog(@"Page %d - viewControllerAfterViewController called on this index", index);
    if (index == NSNotFound) {
        return nil;
    }

    index++;
    if (index == self.imageNames.count) {
        return nil;
    }
    return [self viewControllerAtIndex:index storyboard:viewController.storyboard];
}

#pragma mark - Protocol UI PageViewController Delegate

- (void) pageViewController:(UIPageViewController *)pageViewController willTransitionToViewControllers:(NSArray *)pendingViewControllers {
    NSLog(@"willTransitionToViewControllers to indices");
    for (CloudImageVC *vc in pendingViewControllers) {
        NSLog(@"Page %d",vc.imageIndex);
    }
}

所有这些之后显示的视图实际上是索引4的视图。在第一次转换之后，UIPageViewController的行为似乎与我预期的一样。当我使用PageCurl转换时，它总是按照我期望的方式运行，并且我没有收到任何这些无关的调用

实际生成输出的代码是：

2013-04-19 12:37:33.964 Clouds[496:907] Page 3 - viewControllerAfterViewController called on this index
2013-04-19 12:37:33.988 Clouds[496:907] Page 3 - viewControllerBeforeViewController called on this index
2013-04-19 12:37:34.010 Clouds[496:907] willTransitionToViewControllers to indices
2013-04-19 12:37:34.014 Clouds[496:907] Page 4
2013-04-19 12:37:34.461 Clouds[496:907] Page 4 - viewControllerAfterViewController called on this index

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.pageViewController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil];
    self.pageViewController.delegate = self;
    self.pageViewController.dataSource = self;


    CloudImageVC *startingViewController = [self viewControllerAtIndex:self.currentPage storyboard:self.storyboard];
    NSArray *viewControllers = @[startingViewController];
    [self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:NULL];

    [self addChildViewController:self.pageViewController];
    [self.view addSubview:self.pageViewController.view];

    CGRect pageViewRect = self.view.bounds;
    self.pageViewController.view.frame = pageViewRect;

    [self.pageViewController didMoveToParentViewController:self];

    // Add the page view controller's gesture recognizers to the book view controller's view so that the gestures are started more easily.
    self.view.gestureRecognizers = self.pageViewController.gestureRecognizers;
}

- (CloudImageVC *)viewControllerAtIndex:(NSUInteger)index storyboard:(UIStoryboard *)storyboard {
    // Return the data view controller for the given index.
    if (index >= [self.imageNames count]) {
        return nil;
    }
    self.dataViewController = [self makeDataViewControllerAtIndex:index storyboard:storyboard];
    return self.dataViewController;
 }

- (CloudImageVC *) makeDataViewControllerAtIndex:(NSUInteger)index storyboard:(UIStoryboard *)storyboard {
    // Make and return the data view controller for the given index.
    if (index >= [self.imageNames count]) {
        return nil;
    }
    // Create a new view controller and pass suitable data.
    self.dataViewController = [storyboard instantiateViewControllerWithIdentifier:@"CloudImageVC"];
    self.dataViewController.imageIndex = index;
    //self.dataViewController.cloudImage = nil;
    return self.dataViewController;
}

- (NSUInteger)indexOfViewController:(CloudImageVC *)viewController
{
    // Return the index of the given data view controller.
    // For simplicity, we store the index value in the view controller.
    return viewController.imageIndex;
}

#pragma mark - Page View Controller Data Source

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController {
    NSUInteger index = [self indexOfViewController:(CloudImageVC *)viewController];
    NSLog(@"Page %d - viewControllerBeforeViewController called on this index", index);
    if ((index == 0) || (index == NSNotFound)) {
        return nil;
    }
    index--;
    return [self viewControllerAtIndex:index storyboard:viewController.storyboard];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController {
    NSUInteger index = [self indexOfViewController:(CloudImageVC *)viewController];
    NSLog(@"Page %d - viewControllerAfterViewController called on this index", index);
    if (index == NSNotFound) {
        return nil;
    }

    index++;
    if (index == self.imageNames.count) {
        return nil;
    }
    return [self viewControllerAtIndex:index storyboard:viewController.storyboard];
}

#pragma mark - Protocol UI PageViewController Delegate

- (void) pageViewController:(UIPageViewController *)pageViewController willTransitionToViewControllers:(NSArray *)pendingViewControllers {
    NSLog(@"willTransitionToViewControllers to indices");
    for (CloudImageVC *vc in pendingViewControllers) {
        NSLog(@"Page %d",vc.imageIndex);
    }
}

---

答案在rdelmar的评论中。

是的，我看到过这种模式，这并不是无稽之谈。当页面视图控制器设置为滚动转换时，将在视图层次结构中插入一个滚动视图，额外的调用用于获取上一个和下一个控制器，以便在部分滚动时，您可以同时看到下一个（或上一个）控制器和当前控制器。非常感谢您提供的信息。很高兴知道我没有虫子@rdelmar，但在我的例子中，它不叫“之前”，只叫“下一个”两次。你知道为什么吗？