UIPageViewController学习
UIPageViewController可用于管理多个平行关系的viewCOntroller，提供页面滑动和很炫的翻页效果，可用于引导页切换。
配置属性
UIPageViewController可以配置多个属性进行展示，
| 名称 | 含义 | 值 |
|---|---|---|
| navigationOrientation | 导航的方向：水平or垂直 | UIPageViewControllerNavigationOrientationHorizontal、UIPageViewControllerNavigationOrientationVertical |
| transitionStyle | 翻页的过渡样式：类似书页翻卷或者Scroll滑动 | UIPageViewControllerTransitionStylePageCurl、UIPageViewControllerTransitionStyleScroll |
| spineLocation | 书脊位置，只有书页翻卷效果时有效； | UIPageViewControllerSpineLocationNone：无书脊、UIPageViewControllerSpineLocationMin：根据导航方向，位于屏幕左侧或顶部、UIPageViewControllerSpineLocationMid：位于屏幕中部，同时显示两个页面、UIPageViewControllerSpineLocationMax：根据导航方向，位于屏幕右侧或底部 |
| doubleSided | 屏幕是否显示两个页面，当spineLocation为mid时，其值需设为Yes | 默认为no |
初始化
a) UIPageViewController初始化方法
- (instancetype)initWithTransitionStyle:(UIPageViewControllerTransitionStyle)style
navigationOrientation:(UIPageViewControllerNavigationOrientation)navigationOrientation
options:(NSDictionary<NSString *,id> *)options
参数style对应上述文中transitionStyle，navigationOrientation对应导航方向，options是可选的,但只可以是UIPageViewControllerOptionSpineLocationKey和UIPageViewControllerOptionInterPageSpacingKey组成的字典.
- UIPageViewControllerOptionSpineLocationKey：定义书脊位置，只有其transitionStyle选为UIPageViewControllerTransitionStylePageCurl才有效
- UIPageViewControllerOptionInterPageSpacingKey：定义两个页面的间距，只有其transitionStyle选为UIPageViewControllerTransitionStyleScroll才有效
b) 设置UIPageViewController初始显示的viewController
- (void)setViewControllers:(NSArray<UIViewController *> *)viewControllers
direction:(UIPageViewControllerNavigationDirection)direction
animated:(BOOL)animated
completion:(void (^)(BOOL finished))completion
参数direction值分为UIPageViewControllerNavigationDirectionForward（水平导航时为从左向右，垂直方向时为从上到下）、
UIPageViewControllerNavigationDirectionReverse（水平导航时为从右向左，垂直方向时为从下到上）
DataSource
UIPageViewControllerDataSource提供了四个方法，两个是@required，两个是@optional
@required
//返回前一个页面;如果返回为nil,则会认为当前页面不可以向前滚动或翻页
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
viewControllerBeforeViewController:(UIViewController *)viewController
//返回后一个页面;如果返回为nil,则会认为当前页面不可以向后滚动或翻页
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
viewControllerAfterViewController:(UIViewController *)viewController
@optional
//返回页面总数
- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController
//返回默认展示的页面index
- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController
需要注意的是@optional中的方法是和页面指示器（Page Indicator）相对应的，实现了这两个方法，才可以显示Page Indicator；同时Page Indicator是在scroll过渡效果下显示。
Delegate
UIPageViewControllerDelegate定义了五个方法
//开始滚动或者翻页时执行
- (void)pageViewController:(UIPageViewController *)pageViewController
willTransitionToViewControllers:(NSArray<UIViewController *> *)pendingViewControllers
//结束滚动或者翻页时执行
- (void)pageViewController:(UIPageViewController *)pageViewController
didFinishAnimating:(BOOL)finished
previousViewControllers:(NSArray<UIViewController *> *)previousViewControllers
transitionCompleted:(BOOL)completed
//在书页翻卷效果和旋转屏幕时执行，可以根据屏幕旋转方向设置书脊位置和初始化首页
- (UIPageViewControllerSpineLocation)pageViewController:(UIPageViewController *)pageViewController
spineLocationForInterfaceOrientation:(UIInterfaceOrientation)orientation
//支持的屏幕类型
- (UIInterfaceOrientationMask)pageViewControllerSupportedInterfaceOrientations:(UIPageViewController *)pageViewController
- (UIInterfaceOrientation)pageViewControllerPreferredInterfaceOrientationForPresentation:(UIPageViewController *)pageViewController
实现效果
类似于scroll滚动效果如下图：
滚动效果
类似于书卷翻页效果如下图：
滚动效果
具体实现可以移步代码
可以利用UIPageControl修改page indicator，具体如下
UIPageControl *pageControl = [UIPageControl appearance];
pageControl.pageIndicatorTintColor = [UIColor lightGrayColor];
pageControl.currentPageIndicatorTintColor = [UIColor blackColor];
pageControl.backgroundColor = [UIColor whiteColor];
