UIPageViewController

UIPageViewController是一个用来管理内容页之间导航的容器控制器(container view controller)，其中每个子页面由子视图控制器管理。内容页间导航可以由用户手势触发，也可以由代码控制。

UIPageViewController可以实现图片轮播效果和翻书效果.

初始化PageViewController

public init(transitionStyle style: UIPageViewController.TransitionStyle,
            navigationOrientation: UIPageViewController.NavigationOrientation,
                          options: [UIPageViewController.OptionsKey : Any]? = nil)

初始化方法提供三个参数:

• TransitionStyle

UIPageViewController翻页的过渡样式

  public enum TransitionStyle : Int {
        case pageCurl // Navigate between views via a page curl transition. 卷曲样式类似翻书效果
        case scroll // Navigate between views by scrolling. UIScrollView滚动效果
  }

• NavigationOrientation

UIPageViewController导航方向

 public enum NavigationOrientation : Int {
        case horizontal // 水平导航
        case vertical // 垂直导航
 }

• UIPageViewController.OptionsKey

这个参数是可选的,传入的是对UIPageViewController的一些配置

 public struct OptionsKey : Hashable, Equatable, RawRepresentable {

        public init(rawValue: String)
 }

 extension UIPageViewController.OptionsKey {

    public static let spineLocation: UIPageViewController.OptionsKey
    
    // Key for specifying spacing between pages in options dictionary argument to initWithTransitionStyle:navigationOrientation:options:.
    // Value should be a CGFloat wrapped in an NSNumber. Default is '0'.
    // Only valid for use with page view controllers with transition style 'UIPageViewControllerTransitionStyleScroll'.
    @available(iOS 6.0, *)
    public static let interPageSpacing: UIPageViewController.OptionsKey
}

• spineLocation

这个key只有在TransitionStyle是翻书效果pageCurl的时候才有作用, 它定义的是书脊的位置,值对应着SpineLocation枚举，默认值为UIPageViewController.SpineLocation.min

 public enum SpineLocation : Int {
        case none // Returned if 'spineLocation' is queried when 'transitionStyle' is not 'UIPageViewControllerTransitionStylePageCurl'.
        case min // Requires one view controller.
        case mid // Requires two view controllers.
        case max // Requires one view controller.
 }

• interPageSpacing

这个key只有在TransitionStyle是UIScrollView滚动效果scroll的时候才有作用, 它定义的是两个页面之间的间距(默认间距是0)

数据源和代理

数据源提供了UIPageViewController内容

 weak open var dataSource: UIPageViewControllerDataSource? // If nil, user gesture-driven navigation will be disabled.

UIPageViewControllerDataSource协议

public protocol UIPageViewControllerDataSource : NSObjectProtocol {

    @available(iOS 5.0, *)
    public func pageViewController(_ pageViewController: UIPageViewController,
                                   viewControllerBefore viewController: UIViewController) -> UIViewController?

    @available(iOS 5.0, *)
    public func pageViewController(_ pageViewController: UIPageViewController,
                                   viewControllerAfter viewController: UIViewController) -> UIViewController?

    @available(iOS 6.0, *)
    // The number of items reflected in the page indicator.
    optional public func presentationCount(for pageViewController: UIPageViewController) -> Int 

    @available(iOS 6.0, *)
    // The selected item reflected in the page indicator.
    optional public func presentationIndex(for pageViewController: UIPageViewController) -> Int
}

协议中包含了四个方法,其中两个为@required,另外两个是@optional.

 public func pageViewController(_ pageViewController: UIPageViewController,
                                   viewControllerBefore viewController: UIViewController) -> UIViewController?

该方法是返回前一个页面，如果返回为nil，那么UIPageViewController就会认为当前页面是第一个页面不可以向前滚动或翻页。当NavigationOrientation为horizontal时，那么该方法获得当前页面左边的视图控制器

public func pageViewController(_ pageViewController: UIPageViewController,
                                   viewControllerAfter viewController: UIViewController) -> UIViewController?

该方法返回后一个页面，如果返回为nil，那么UIPageViewController就会认为当前页面是最后一个页面不可以向后滚动或翻页。当NavigationOrientation为horizontal时，那么该方法获得是当前页面右边的视图控制器

代理（delegate）自定义UIPageViewController的行为

weak open var delegate: UIPageViewControllerDelegate?

UIPageViewControllerDelegate协议

public protocol UIPageViewControllerDelegate : NSObjectProtocol {

    @available(iOS 6.0, *)
    optional public func pageViewController(_ pageViewController: UIPageViewController,
                                            willTransitionTo pendingViewControllers: [UIViewController])

    @available(iOS 5.0, *)
    optional public func pageViewController(_ pageViewController: UIPageViewController,
                                            didFinishAnimating finished: Bool,
                                            previousViewControllers: [UIViewController],
                                            transitionCompleted completed: Bool)

    @available(iOS 5.0, *)
    optional public func pageViewController(_ pageViewController: UIPageViewController,
                                            spineLocationFor orientation: UIInterfaceOrientation) -> UIPageViewController.SpineLocation


    @available(iOS 7.0, *)
    optional public func pageViewControllerSupportedInterfaceOrientations(_ pageViewController: UIPageViewController) -> UIInterfaceOrientationMask

    @available(iOS 7.0, *)
    optional public func pageViewControllerPreferredInterfaceOrientationForPresentation(_ pageViewController: UIPageViewController) -> UIInterfaceOrientation
}

协议中有5各方法

optional public func pageViewController(_ pageViewController: UIPageViewController,
                     willTransitionTo pendingViewControllers: [UIViewController])

该方法是UIPageViewController开始滚动或翻页的时候触发

optional public func pageViewController(_ pageViewController: UIPageViewController,
                                 didFinishAnimating finished: Bool,
                                     previousViewControllers: [UIViewController],
                               transitionCompleted completed: Bool)

该方法是在UIPageViewController结束滚动或翻页的时候触发

optional public func pageViewController(_ pageViewController: UIPageViewController,
                                 spineLocationFor orientation: UIInterfaceOrientation) -> UIPageViewController.SpineLocation

该方法在TransitionStyle是pageCurl并且横竖屏状态变化的时候触发，我们可以重新设置书脊的位置，比如：如果屏幕是竖屏状态的时候我们就设置书脊位置是min或max, 如果屏幕是横屏状态的时候我们可以设置书脊位置是mid

最后两个方法设置了UIPageViewController支持的屏幕类型

重要的方法和属性

isDoubleSided

属性默认为NO，如果我们当前屏幕仅展示一个页面那么不用设置这个属性，如果设置了UIPageViewControllerSpineLocationMid这个选项，效果是翻开的书这样屏幕展示的就是两个页面，这个属性就必须设置为true了.

open var isDoubleSided: Bool // Default is 'NO'.

setViewControllers

open func setViewControllers(_ viewControllers: [UIViewController]?,
                             direction: UIPageViewController.NavigationDirection,
                             animated: Bool,
                             completion: ((Bool) -> Void)? = nil)

这个方法是设置UIPageViewController初始显示的页面，如果doubleSided设为true了,那么viewControllers这个参数至少包含两个视图控制器

NavigationDirection

// Only pertains to 'UIPageViewControllerTransitionStylePageCurl'.
public enum NavigationDirection : Int {
     case forward  // 导航到下一个页面
     case reverse  // 导航到上一个页面
}

使用

简单的实现滑动切换视图，即轮播图

class PageViewController: UIViewController {

    // 懒加载创建UIPageViewController
    lazy var pageViewController: UIPageViewController = {
        // 设置水平滚动
        let pageVc = UIPageViewController(transitionStyle: .scroll,
                                          navigationOrientation: .horizontal,
                                          options: nil)
        pageVc.dataSource = self
        pageVc.delegate = self
        return pageVc
    }()
    // 简单的3个UIViewController
    var viewControllers: [UIViewController] {
        return [RedViewController(), YellowViewController(), BlueViewController()]
    }
    var currentIndex: Int = 0

    override func viewDidLoad() {
        super.viewDidLoad()
        addPageViewController()

        // 设置初始化显示视图控制器
        pageViewController.setViewControllers([viewControllers[currentIndex]],
                                              direction: .forward,
                                              animated: true,
                                              completion: nil)
    }

    func addPageViewController() {
        self.addChild(pageViewController)
        pageViewController.view.frame = self.view.frame
        view.addSubview(pageViewController.view)
        pageViewController.didMove(toParent: self)
    }
}

扩展PageViewController实现数据源和代理协议

extension PageViewController: UIPageViewControllerDataSource, UIPageViewControllerDelegate {
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        // 显示前一个页面，保证数组不越界
        if currentIndex - 1 >= 0 {
            currentIndex -= 1
            return viewControllers[currentIndex]
        }
        return nil
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        // 显示后一个视图页面
        if currentIndex + 1 < viewControllers.count {
            currentIndex += 1
            return viewControllers[currentIndex]
        }
        return nil
    }

    func pageViewController(_ pageViewController: UIPageViewController, willTransitionTo pendingViewControllers: [UIViewController]) {
        print("willTransition - 开始滚动")
    }

    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        print("didFinishAnimating - 结束滚动")
    }
}

实现效果如下

2.gif

相关实战

• UIPageViewController and storyboard

• TabPageViewController
  

  demo2.gif

• Parchment
  
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  68747470733a2f2f73332d75732d776573742d312e616d617a6f6e6177732e636f6d2f70617263686d656e742d73776966742f70617263686d656e742d756e73706c6173682e676966.gif

参考

UIPageViewController