UIPageViewController怎么手动切换下一页

我用的xcode自带的模板项目
一共ModelController，DataViewController，RootViewController 三个。
[code=objc]//

#import "ModelController.h"
#import "DataViewController.h"

@interface ModelController()
@property (readonly, strong, nonatomic) NSArray *pageData;
@end

@implementation ModelController

• (id)init
  {
  self = [super init];
  if (self) {
  // Create the data model.
  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
  _pageData = [[dateFormatter monthSymbols] copy];
  }
  return self;
  }

• (DataViewController *)viewControllerAtIndex:(NSUInteger)index storyboard:(UIStoryboard *)storyboard
  {
  
  // Return the data view controller for the given index.
  if (([self.pageData count] == 0) || (index >= [self.pageData count])) {
  return nil;
  }

  // Create a new view controller and pass suitable data.
  DataViewController *dataViewController = [storyboard instantiateViewControllerWithIdentifier:@"DataViewController"];
  dataViewController.dataObject = self.pageData[index];
  return dataViewController;
  }

• (NSUInteger)indexOfViewController:(DataViewController *)viewController
  {
  
  // Return the index of the given data view controller.
  // For simplicity, this implementation uses a static array of model objects and the view controller stores the model object; you can therefore use the model object to identify the index.
  return [self.pageData indexOfObject:viewController.dataObject];
  }

#pragma mark - Page View Controller Data Source

• (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
  {
  NSUInteger index = [self indexOfViewController:(DataViewController *)viewController];
  if ((index == 0) || (index == NSNotFound)) {
  return nil;
  }

  index--;
  return [self viewControllerAtIndex:index storyboard:viewController.storyboard];
  }

• (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
  {
  NSUInteger index = [self indexOfViewController:(DataViewController *)viewController];
  if (index == NSNotFound) {
  return nil;
  }

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

@end
[/code]

RootViewController的代码：
[code=objc]@interface ModelController()
@property (readonly, strong, nonatomic) NSArray *pageData;
@end

@implementation ModelController

• (id)init
  {
  self = [super init];
  if (self) {
  // Create the data model.
  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
  _pageData = [[dateFormatter monthSymbols] copy];
  }
  return self;
  }

• (DataViewController *)viewControllerAtIndex:(NSUInteger)index storyboard:(UIStoryboard *)storyboard
  {
  
  // Return the data view controller for the given index.
  if (([self.pageData count] == 0) || (index >= [self.pageData count])) {
  return nil;
  }

  // Create a new view controller and pass suitable data.
  DataViewController *dataViewController = [storyboard instantiateViewControllerWithIdentifier:@"DataViewController"];
  dataViewController.dataObject = self.pageData[index];
  return dataViewController;
  }

• (NSUInteger)indexOfViewController:(DataViewController *)viewController
  {
  
  // Return the index of the given data view controller.
  // For simplicity, this implementation uses a static array of model objects and the view controller stores the model object; you can therefore use the model object to identify the index.
  return [self.pageData indexOfObject:viewController.dataObject];
  }

#pragma mark - Page View Controller Data Source

• (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
  {
  NSUInteger index = [self indexOfViewController:(DataViewController *)viewController];
  if ((index == 0) || (index == NSNotFound)) {
  return nil;
  }

  index--;
  return [self viewControllerAtIndex:index storyboard:viewController.storyboard];
  }

• (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
  {
  NSUInteger index = [self indexOfViewController:(DataViewController *)viewController];
  if (index == NSNotFound) {
  return nil;
  }

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

@end[/code]

这是DataViewController

• (void)viewWillAppear:(BOOL)animated { [super viewWillAppear:animated]; self.dataLabel.text = [self.dataObject description]; }

我要在DataViewController里进行翻页 要怎么办？ 我试了把ModelViewController传进来 调用 [_modelViewController viewControllerAtIndex:index storyboard:viewController.storyboard];
没有效果

求大神帮助 ，我是新手