iOS - UIPageViewControllerDataSource 方法调用了两次

Question

我发现这两个UIPageViewControllerDataSource方法有一个奇怪的问题:第一次进入page view controller场景，在controller的内容上拖动，不管拖动的方向是什么，都调用数据源方法。我想当我在第一页并向右拖动时，这意味着第一页之前没有更多页面，这两个方法都不应该被调用。如果我向左拖动，则只应调用 after 方法。

我关注了this post设置 View Controller (除了我在 Storyboard上没有单独的页面 View Controller 。我使用传统的 [UIPAgeViewController alloc] init] 方法来实例化 Controller )。下面是我的代码:

对于实际显示页面 View Controller 内容的 View Controller (只显示viewDidLoad的相关部分):

 - (void)viewDidLoad 
{
    // initialize page view controller
    _pageViewController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil];
    self.pageViewController.delegate = self;
    self.pageViewController.dataSource = self;

    // set up the initial scene of the page view controller
    UIViewController *viewController = [self viewControllerAtIndex:0];
    [self.pageViewController setViewControllers:@[viewController]
                                      direction:UIPageViewControllerNavigationDirectionForward
                                       animated:NO
                                     completion:nil];

    // adjust the size of the page view controller, -44 to show the buttons at the bottom
    self.pageViewController.view.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height - 44);

    // display the content of the page view controller
    [self addChildViewController:self.pageViewController];
    [self.view addSubview:self.pageViewController.view];
    [self.pageViewController didMoveToParentViewController:self];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
      viewControllerBeforeViewController:(UIViewController *)viewController
{
    NSUInteger index = ((PWCPageContentViewController *)viewController).index;
    if (index == 0 || index == NSNotFound) {
        return nil;
    }
    --index;
    return [self viewControllerAtIndex:index];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
       viewControllerAfterViewController:(UIViewController *)viewController
{
    NSUInteger index = ((PWCPageContentViewController *)viewController).index;
    if (index == self.numberOfPages - 1 || index == NSNotFound) {
        return nil;
    }
    ++index;
    return [self viewControllerAtIndex:index];
}

- (PWCPageContentViewController *)viewControllerAtIndex:(NSUInteger)index
{
    PWCPageContentViewController *viewController =
    [self.storyboard instantiateViewControllerWithIdentifier:@"PageContentViewController"];
    viewController.index = index;
    NSString *text = [self.notes getNoteAtIndex:index];
    [viewController.textView setText:text];

    return viewController;
}

对于 PWCPageContentViewController.h:

#import <UIKit/UIKit.h>

@class PWCNotes;

@interface PWCPageContentViewController : UIViewController <UITextViewDelegate>

@property NSUInteger index;
@property (weak, nonatomic) IBOutlet UITextView *textView;

- (void)dismissKeyboard;

@end

对于 PWCPageContentViewController.m:

#import "PWCPageContentViewController.h"

@interface PWCPageContentViewController ()

@end

@implementation PWCPageContentViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.textView.delegate = self;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)dismissKeyboard
{
    if ([self.textView isFirstResponder]) {
        // dismiss the keyboard when hitting save
        [self.textView resignFirstResponder];
    }
}

@end

这是一个已知问题还是我遗漏了什么？

Answer 1

Swift 中这个问题的解决方案:

我在使用超过 3 个 UIPageViewController 时遇到了错误(例如尝试使用 4 个 UIPageViewController，使用@Rashad 的代码片段)。问题来自缺少且未实现的可选 UIPageViewControllerDelegate 方法，这导致 UIPageControl 变得疯狂和不稳定。

请在下面找到修复错误的具体方法:

/*
    Optional UIPageViewControllerDelegate method

    Sent when a gesture-initiated transition ends. The 'finished' parameter indicates whether
    the animation finished, while the 'completed' parameter indicates whether the transition completed or bailed out (if the user let go early).
*/
func pageViewController(pageViewController: UIPageViewController,
    didFinishAnimating finished: Bool,
    previousViewControllers: [AnyObject],
    transitionCompleted completed: Bool)
{
    // Turn is either finished or aborted
    if (completed && finished) {
        let currentDisplayedViewController = self.pageViewController!.viewControllers[0] as! ContentViewController
        self.pageControl.currentPage = currentDisplayedViewController.index
    }
}

如果您想获得完整的工作项目，请在下面找到 Github 链接:

( Github link of the project )