在故事板中翻页时更新currentIndex标题

Question

在故事板中使用导航控制器作为rootviewcontroller。我希望在翻页时更新currentIndex。 Storyboard push segue正在显示这个pdfviewcontroller场景，我首先尝试显示标题。

- (void) displaycurrentIndex:(NSUInteger)currentIndex {

self.navigationItem.title = [NSString stringWithFormat:
                                              @"Page %i of %i",
                                              currentIndex,
                                             CGPDFDocumentGetNumberOfPages(pdf)];

}

Pageviewcontroller其他类有数据源方法在pdfviewcontroller类中正向和反向显示pdf页面

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

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

在pdfviewcontroller中尝试了这种方法但没有工作

 - (void)updatecurrentpagenumber {

if (currentIndex == CGPDFDocumentGetNumberOfPages(pdf) - 1) {

    [self displaycurrentIndex:currentIndex + 1];

}

//page = [modelArray objectAtIndex:currentIndex + 1];

else if  (currentIndex == 0) {

    [self displaycurrentIndex:currentIndex - 1];
}
//page = [modelArray objectAtIndex:currentIndex - 1];

 }

编辑：

尝试了这一点，但仍然没有更新currentIndex

- (void)updatecurrentIndex:(NSUInteger)currentIndex {

totalPages = (int)CGPDFDocumentGetNumberOfPages(pdf);

if (currentIndex<totalPages -1)
{
     [self displaycurrentIndex:currentIndex + 1];
}
else
{
    [self displaycurrentIndex:currentIndex - 1];
}

感谢您的帮助。