Question

我正在使用UIPageViewController和UIPageControl。由于某种原因，索引上的0-> 1转换持续被调用两次。例如，使用以下代码：

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
    self.index --;

    NSLog(@")self.index --;");
    if(self.index<1){
        self.index = 1;
    }

    return [self viewControllerAtIndex: self.index];
}

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

        NSLog(@")self.index ++;");
    self.index ++;

    if(self.index==5){
        [self dismissViewControllerAnimated:NO completion:nil];
        return nil;
    }

    return [self viewControllerAtIndex: self.index];
}

- (UIViewController *)viewControllerAtIndex:(NSUInteger)index{
    self.index = index;
    NSLog(@"index is %d", self.index);
    UIViewController *next1 = [[UIViewController alloc] init];
    next1.view.backgroundColor = BACKGROUND_COLOR;
    next1.view.userInteractionEnabled = NO;
    return next1;
}

- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController
{
    return 5;
}

-(NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController
{
    return self.index;
}

我得到了这个输出：

2014-12-22 12:10:04.349 BuzzJudge[665:142581] index is 0
2014-12-22 12:10:05.030 BuzzJudge[665:142581] )self.index ++;
2014-12-22 12:10:05.031 BuzzJudge[665:142581] index is 1
2014-12-22 12:10:05.032 BuzzJudge[665:142581] )self.index --;
2014-12-22 12:10:05.032 BuzzJudge[665:142581] index is 1
2014-12-22 12:10:05.444 BuzzJudge[665:142581] )self.index ++;
2014-12-22 12:10:05.445 BuzzJudge[665:142581] index is 2
2014-12-22 12:10:05.844 BuzzJudge[665:142581] )self.index ++;
2014-12-22 12:10:05.845 BuzzJudge[665:142581] index is 3
2014-12-22 12:10:06.263 BuzzJudge[665:142581] )self.index ++;
2014-12-22 12:10:06.264 BuzzJudge[665:142581] index is 4
2014-12-22 12:10:06.627 BuzzJudge[665:142581] )self.index ++;

如果我略微修改代码以允许0索引（我最初在做什么）它变得更糟，在0和1索引之间反弹而不是仅仅0-> 1，如下所示：

2014-12-22 12:13:46.404 BuzzJudge[672:144489] index is 0
2014-12-22 12:13:48.147 BuzzJudge[672:144489] )self.index ++;
2014-12-22 12:13:48.148 BuzzJudge[672:144489] index is 1
2014-12-22 12:13:48.149 BuzzJudge[672:144489] )self.index --;
2014-12-22 12:13:48.150 BuzzJudge[672:144489] index is 0
2014-12-22 12:13:48.561 BuzzJudge[672:144489] )self.index ++;
2014-12-22 12:13:48.562 BuzzJudge[672:144489] index is 1

使用此修改后的代码：

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
    self.index --;

    NSLog(@")self.index --;");
    if(self.index<0){
        self.index = 0;
    }

    return [self viewControllerAtIndex: self.index];
}

我已经调整了我的代码试图摆脱这个，包括将self.index初始化为0或1，并使用我提供的那种视图控制器，但这并没有导致它。有没有人见过这个或知道是什么导致它？我在SO上找不到任何东西，但也许我使用了错误的搜索词。

Answer 1

您的问题可能是框架提前缓存了额外的数据，而您的代码的副作用导致了问题。您应该避免UIPageViewControllerDataSource方法中的那些副作用：这些方法应该返回数据，而不执行任何其他操作。

执行此操作的正确方法是一些额外的工作，但它使代码更清晰，更易于维护。我会让每个页面成为UIViewController的自定义子类，它知道它的页面索引，就像这样就足够了：

MyPageViewControllerPage.h

@interface MyPageViewControllerPage : UIViewController {
@property NSInteger index;
+(instancetype) pageWithIndex:(NSInteger)index;
}

MyPageViewControllerPage.m

@implementation MyPageViewControllerPage {
+(instancetype) pageWithIndex:(NSInteger)index {
    MyPageViewControllerPage* page = [[MyPageViewControllerPage alloc]init];
    page.index = index;
    page.view.backgroundColor = BACKGROUND_COLOR;
    page.view.userInteractionEnabled = NO;
}
}

然后在您的DataSource实现中，更新它以使用这个新类：

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
    MyPageViewControllerPage* page = (MyPageViewControllerPage*)viewController;
    if (page.index <= 0) return nil;
    else return [self viewControllerAtIndex: page.index - 1];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
    MyPageViewControllerPage* page = (MyPageViewControllerPage*)viewController;

    // Limit to the right number of pgaes, but allow one extra at the end to signal dismissal
    if (page.index > self.numberOfPages) return nil;
    else return [self viewControllerAtIndex: page.index + 1];
}

- (UIViewController *)viewControllerAtIndex:(NSUInteger)index {
    return [MyPageViewControllerPage pageWithIndex: index];
}

这样，UIKit框架可以为您管理一切。如果你想在到达最后一页时让页面VC被忽略，我会像{em}那样实现UIPageViewControllerDelegate方法pageViewController:willTransitionToViewControllers:：

-(void)pageViewController:(UIPageViewController *)pageViewController willTransitionToViewControllers:(NSArray *)pendingViewControllers {
    MyPageViewControllerPage* page = (MyPageViewControllerPage*)pendingViewControllers[0];
    if (page.index == self.numberOfPages) {
        [self dismissViewControllerAnimated:YES completion:nil];
    }
}

确保您在界面构建器或viewDidLoad中设置了委托（如果您还没有）：

-(void)viewDidLoad {
     // ... other initialization ...    
     self.pageViewController.delegate = self;
 }

UIPageViewController在索引1上加倍（0-> 1-> 0-> 1-> 2-> 3 ...）

1 个答案:

MyPageViewControllerPage.h

MyPageViewControllerPage.m