以编程方式创建水平分页 UIPageViewController

1. 由 UIPageViewController 管理的初始视图控制器数组。添加一个基本视图控制器类，它具有属性 identifier，用于在使用 UIPageViewController 数据源方法时识别视图控制器。让视图控制器从该基类继承。

UIViewController *firstVC = [[UIViewController alloc] init]; 
firstVC.identifier = 0  
UIViewController *secondVC = [[UIViewController alloc] init];   
secondVC.identifier = 1
NSArray *viewControllers = [[NSArray alloc] initWithObjects: firstVC, secondVC, nil];

2. 创建 UIPageViewController 实例。

UIPageViewController *pageViewController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll
                                                                           navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal
                                                                                         options:nil];

3. 数据源是必须实现 UIPageViewControllerDataSource 协议的当前类。

pageViewController.dataSource = self;

4. setViewControllers 将只添加第一个视图控制器，接下来将使用数据源方法添加到堆栈中

if (viewControllers.count) {
    [pageViewController setViewControllers:@[[viewControllers objectAtIndex:0]]
                                 direction:UIPageViewControllerNavigationDirectionForward
                                  animated:NO
                                completion:nil];
}

5. 添加 UIPageViewController 作为子视图控制器，以便从它的父视图控制器 appearance 和 rotation 事件接收。

 [self addChildViewController:pageViewController];
 pageViewController.view.frame = self.view.frame;
 [self.view addSubview:pageViewController.view];
 [pageViewController didMoveToParentViewController:self];

6. 实现 UIPageViewControllerDataSource 方法

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
      viewControllerBeforeViewController:(UIViewController *)viewController
{
    index = [(Your View Controler Base Class *)viewController identifier];
    index--;
    return [self childViewControllerAtIndex:index];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
       viewControllerAfterViewController:(UIViewController *)viewController
{
    index = [(Your View Controler Base Class *)viewController identifier];
    index++;
    return [self childViewControllerAtIndex:index];
}

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

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

7. 使用索引返回视图控制器的实用程序方法，如果索引超出范围，则返回 nil。

- (UIViewController *)childViewControllerAtIndex:(NSInteger)index
{
    if (index <= ([viewControllers count] - 1)) {
        return [viewControllers objectAtIndex:index];
    } else {
        return nil;
    }
}