PageViewController 委托函数调用了两次

Question

我正在使用 UIPageViewController 为我的应用程序制作产品导览。

我点击了这个链接http://www.appcoda.com/uipageviewcontroller-tutorial-intro/

我正在做的是根据我得到的索引值在滑动时更改 “root VC” 的背景颜色的简单任务，但是由于委托函数被调用两次，我的索引值是不正确，因此，我无法正确处理，下面是我的代码

#import "APPViewController.h"
#import "APPChildViewController.h"

@interface APPViewController ()

@end

@implementation APPViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    self.pageController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil];

    self.pageController.dataSource = self;
    [[self.pageController view] setFrame:CGRectMake(0, 0, 320, 500)];

    APPChildViewController *initialViewController = [self viewControllerAtIndex:0];

    NSArray *viewControllers = [NSArray arrayWithObject:initialViewController];

    [self.pageController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];

    [self addChildViewController:self.pageController];
    [[self view] addSubview:[self.pageController view]];
    [self.pageController didMoveToParentViewController:self];

}

- (void)didReceiveMemoryWarning {

    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.

}

- (APPChildViewController *)viewControllerAtIndex:(NSUInteger)index {

    APPChildViewController *childViewController = [[APPChildViewController alloc] initWithNibName:@"APPChildViewController" bundle:nil];
    childViewController.index = index;
    childViewController.view.backgroundColor = [UIColor clearColor];

    if(index == 0)
    {
          self.view.backgroundColor = [UIColor redColor];
     }

    if(index == 1)
    {
          self.view.backgroundColor = [UIColor blueColor];
     }

    if(index == 2)
    {
          self.view.backgroundColor = [UIColor greenColor];
     }


    return childViewController;

}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController {

    NSUInteger index = [(APPChildViewController *)viewController index];

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

    // Decrease the index by 1 to return
    index--;

   return [self viewControllerAtIndex:index];

}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController {

    NSUInteger index = [(APPChildViewController *)viewController index];

    index++;

    if (index == 3) {
        return nil;
    }

   return [self viewControllerAtIndex:index];

}

- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController {
    // The number of items reflected in the page indicator.
    return 3;
}

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController {
    // The selected item reflected in the page indicator.
    return 0;
}

请帮帮我，我不知道哪里出错了

问候 兰吉特

Answer 1

我遇到了同样的问题，终于找到了原因。 当页面视图控制器的 Transition 样式设置为“Page Curl”时，会调用两次委托方法。

当过渡样式设置为“Page Curl”时，动作就像翻书一样。您翻一页，页码增加 2。 对页面视图控制器应用相同的概念，将 2 个视图控制器转换为 Page Curl 样式：一个是您看到的视图控制器，另一个视图控制器位于卷曲视图的另一侧。

将过渡样式改为“滚动”即可解决问题

这可以通过属性检查器中的情节提要完成，如下所示：

您也可以通过将 UIPageViewController.transitionStyle 属性设置为 UIPageViewControllerTransitionStyleScroll 来通过代码进行更改。

希望对你有帮助

Answer 2

找了很多。

我收到了：

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

2 个函数用于获取当前 pageViewController 后面或前面的 pageViewController。

我认为获取当前 pageViewController 很困难

我的建议：

在 UIPageViewControllerDelegate 中，它有一个功能：

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

这个函数给你一个pendingViewControllers 数组和当前pageViewController 数组。 所以你可以这样实现：

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


if([pendingViewControllers count]>0)
  {
     NSUInteger index =[(APPChildViewController*)[pendingViewControllers objectAtIndex:0] index];

    if(index == 0)
    {
        self.view.backgroundColor = [UIColor redColor];
    }

    if(index == 1)
    {
        self.view.backgroundColor = [UIColor blueColor];
    }

    if(index == 2)
    {
        self.view.backgroundColor = [UIColor greenColor];
    }


  }
}

在 viewDidLoad 中，添加：

    self.pageController.delegate = self;

    self.view.backgroundColor = [UIColor redColor]; //set first background.

在 'APPViewController.h' 中你确定添加：

@interface APPViewController : UIViewController<UIPageViewControllerDataSource,UIPageViewControllerDelegate>

记住：删除这段代码（在'viewControllerAtIndex'函数中）

if(index == 1)
{
    self.view.backgroundColor = [UIColor redColor];
}

if(index == 2)
{
    self.view.backgroundColor = [UIColor blueColor];
}

if(index == 3)
{
    self.view.backgroundColor = [UIColor greenColor];
}

如果您有任何问题，请告诉我。

Answer 3

替换这两个方法并编译，

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController {

    NSUInteger index = [(APPChildViewController *)viewController index];
    if (index == 0)
    {
        self. view.backgroundColor = [UIColor redColor];
        return nil;
    }

    if(index == 1)
    {
        self.view.backgroundColor = [UIColor blueColor];
    }

    if(index == 2)
    {
        self.view.backgroundColor = [UIColor greenColor];
    }
    if(index == 3)
    {
        self.view.backgroundColor = [UIColor brownColor];
    }
    /*if(index == 4)
    {
        self.view.backgroundColor = [UIColor whiteColor];
    }*/

    // Decrease the index by 1 to return
    index--;

    return [self viewControllerAtIndex:index];

}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController {

    NSUInteger index = [(APPChildViewController *)viewController index];
    /*if(index == 0)
    {
        self.view.backgroundColor = [UIColor redColor];
    }*/
    if(index == 1)
    {
        self.view.backgroundColor = [UIColor blueColor];
    }

    if(index == 2)
    {
        self.view.backgroundColor = [UIColor greenColor];
    }
    if(index == 3)
    {
        self.view.backgroundColor = [UIColor brownColor];
    }
    if(index == 4)
    {
        self.view.backgroundColor = [UIColor whiteColor];
        return nil;
    }

    /*if (index == 5) {
        return nil;
    }*/
    index++;

    return [self viewControllerAtIndex:index];

}

并将其添加到- (void)viewDidLoad {的末尾

self.view.backgroundColor = [UIColor redColor];