UIPageViewControllerDataSource在第一次运行时调用viewControllerAfterViewController两次

Question

我知道这可能是重复的，但我尝试了在线发现的其他解决方案，但似乎没有一个解决我的问题。

我有一个显示4个UIViewControllers的pageViewController。 首先滚动pageController滑动到第三个View控制器，但显示第二个ViewController。

这是我的代码：

_contentPageRestorationIDs = [[NSArray alloc]initWithObjects:@"PRPeripheralsOriantaionVC",@"PRSessionAnalysisDataVC", @"PRNavigationVC",@"PRVideoVC", nil];


- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController
{
return self.contentPageRestorationIDs.count;
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
        NSString *vcRestorationID = viewController.restorationIdentifier;
    NSUInteger index = [self.contentPageRestorationIDs indexOfObject:vcRestorationID];
    NSLog(@"viewControllerBeforeViewController %@",vcRestorationID);

    if (index == 0)
    {
        return nil;
    }

    index--;
    return [self viewControllerAtIndex:index ];

}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
    NSString *vcRestorationID = viewController.restorationIdentifier;
NSLog(@"viewControllerAfterViewController %@",vcRestorationID);

    NSUInteger index = [self.contentPageRestorationIDs indexOfObject:vcRestorationID];
    index ++;
    if (index == self.contentPageRestorationIDs.count )
    {
        return nil;
    }

    return [self viewControllerAtIndex:index ];

}
- (void)pageViewController:(UIPageViewController *)pageViewController willTransitionToViewControllers:(NSArray *)pendingViewControllers
{
   NSLog(@"willTransitionToViewControllers %@ %lu",pendingViewControllers,(unsigned long)index);

}

-(void)pageViewController:(UIPageViewController *)pageViewController didFinishAnimating:(BOOL)finished previousViewControllers:(NSArray *)previousViewControllers transitionCompleted:(BOOL)completed
{
NSLog(@"didFinishAnimating %@",previousViewControllers);
}

Answer 1

您有错误，请更新您的数据源方法：

h文件

@interface ViewController : UIPageViewController

@end

m档案

#import "ViewController.h"

@interface ViewController ()<UIPageViewControllerDataSource>
@property (strong, nonatomic) NSArray *pageColors;
@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.pageColors = @[@"green", @"yellow", @"black", @"red"];
    self.dataSource = self;


    UIViewController *startingViewController = [self viewControllerAtIndex:0];
    NSArray *viewControllers = @[startingViewController];
    [self setViewControllers:viewControllers
                   direction:UIPageViewControllerNavigationDirectionForward
                    animated:NO
                  completion:nil];
}

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

#pragma mark - Private method
- (UIViewController *)viewControllerAtIndex:(NSUInteger)index
{
    if (([self.pageColors count] == 0) || (index >= [self.pageColors count])) {
        return nil;
    }

    NSString* pageColor = self.pageColors[index];

    // Create a new view controller and pass suitable data.
    UIViewController *pageContentViewController = [self.storyboard instantiateViewControllerWithIdentifier:pageColor];

    return pageContentViewController;
}

#pragma mark - Page View Controller Data Source
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
      viewControllerBeforeViewController:(UIViewController *)viewController
{
    NSString * identifier = viewController.restorationIdentifier;
    NSUInteger index = [self.pageColors indexOfObject:identifier];

    if ((index == 0) || (index == NSNotFound)) {
        return nil;
    }

    index--;
    return [self viewControllerAtIndex:index];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
       viewControllerAfterViewController:(UIViewController *)viewController
{
    NSString * identifier = viewController.restorationIdentifier;
    NSUInteger index = [self.pageColors indexOfObject:identifier];

    if (index == NSNotFound) {
        return nil;
    }

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

- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController
{
    return [self.pageColors count];
}

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController
{
    return 0;
}
@end

不要忘记为每个视图控制器更改Storyboard ID及其颜色（[@“green”，@“yellow”，@“black”，@“red”]）。 例如，对于读取视图控制器：

You can find here very useful tutorial.

Answer 2

正确的方法是为每个视图控制器定义pageIndex属性，然后在页面视图委托方法中设置它，使用索引方法的视图控制器，最终想要的代码应该是页面视图委托方法，将索引传递给索引路径的视图控制器并返回检索到的VC，就是这样。