我有一个 UIPageViewController，当我们向左或向右滑动翻页时，它可以正常工作。
class ViewController: UIViewController, UIPageViewControllerDataSource {
...
}
现在我打算在页面上也提供上一个/下一个按钮，以便通过单击这些按钮来翻页。
如何触发左右滑动行为或以编程方式翻页？
这是 Swift 语言的问题，而不是 Objective-C。
【问题讨论】：
标签： ios swift uiviewcontroller uipageviewcontroller
通常没有必要摆弄页面索引等等。您可能已经在实现一个dataSource: UIPageViewControllerDataSource，它包含了显示上一个或下一个 ViewController 所需的所有内容。
Swift 5 示例：
extension UIPageViewController {
func goToNextPage() {
guard let currentViewController = self.viewControllers?.first else { return }
guard let nextViewController = dataSource?.pageViewController( self, viewControllerAfter: currentViewController ) else { return }
setViewControllers([nextViewController], direction: .forward, animated: false, completion: nil)
}
func goToPreviousPage() {
guard let currentViewController = self.viewControllers?.first else { return }
guard let previousViewController = dataSource?.pageViewController( self, viewControllerBefore: currentViewController ) else { return }
setViewControllers([previousViewController], direction: .reverse, animated: false, completion: nil)
}
}
这样您就可以保证您要转换到的页面正是PageViewController's 内置手势将触发的页面。
【讨论】：
presentationIndexForPageViewController。在我的pageItemViewController 上，我声明了一个名为itemIndex 的变量。我将如何在此扩展程序中设置它？
Swift 3 版本的SuitedSloth 的答案（对animated 参数进行了小调整，因为我需要它在默认情况下进行动画处理，但仍然在函数中使用参数) 以防万一有人需要：
extension UIPageViewController {
func goToNextPage(animated: Bool = true) {
guard let currentViewController = self.viewControllers?.first else { return }
guard let nextViewController = dataSource?.pageViewController(self, viewControllerAfter: currentViewController) else { return }
setViewControllers([nextViewController], direction: .forward, animated: animated, completion: nil)
}
func goToPreviousPage(animated: Bool = true) {
guard let currentViewController = self.viewControllers?.first else { return }
guard let previousViewController = dataSource?.pageViewController(self, viewControllerBefore: currentViewController) else { return }
setViewControllers([previousViewController], direction: .reverse, animated: animated, completion: nil)
}
}
【讨论】：
{ completed in self.delegate?.pageViewController?(self, didFinishAnimating: true, previousViewControllers: [], transitionCompleted: completed) }
使用此功能并为您想要的动画设置过渡样式。
【讨论】：
这里也是带有代表的 swift 4 实现。
由于我也使用 UIPageViewControllerDelegate，并且大多数 setViewController 解决方案都没有调用委托方法。
感谢Andrew Duncan's 对代表的评论。
// Functions for clicking next and previous in the navbar, Updated for swift 4
@objc func toNextArticle(){
guard let currentViewController = self.viewControllers?.first else { return }
guard let nextViewController = dataSource?.pageViewController( self, viewControllerAfter: currentViewController ) else { return }
// Has to be set like this, since else the delgates for the buttons won't work
setViewControllers([nextViewController], direction: .forward, animated: true, completion: { completed in self.delegate?.pageViewController?(self, didFinishAnimating: true, previousViewControllers: [], transitionCompleted: completed) })
}
@objc func toPreviousArticle(){
guard let currentViewController = self.viewControllers?.first else { return }
guard let previousViewController = dataSource?.pageViewController( self, viewControllerBefore: currentViewController ) else { return }
// Has to be set like this, since else the delgates for the buttons won't work
setViewControllers([previousViewController], direction: .reverse, animated: true, completion:{ completed in self.delegate?.pageViewController?(self, didFinishAnimating: true, previousViewControllers: [], transitionCompleted: completed) })
}
【讨论】：
这是一个快速的实现：
private func slideToPage(index: Int, completion: (() -> Void)?) {
let count = //Function to get number of viewControllers
if index < count {
if index > currentPageIndex {
if let vc = viewControllerAtIndex(index) {
self.pageViewController.setViewControllers([vc], direction: UIPageViewControllerNavigationDirection.Forward, animated: true, completion: { (complete) -> Void in
self.currentPageIndex = index
completion?()
})
}
} else if index < currentPageIndex {
if let vc = viewControllerAtIndex(index) {
self.pageViewController.setViewControllers([vc], direction: UIPageViewControllerNavigationDirection.Reverse, animated: true, completion: { (complete) -> Void in
self.currentPageIndex = index
completion?()
})
}
}
}
}
viewControllerAtIndex(index: Int) -> UIViewController? 是我自己的函数，可以让正确的视图控制器滑动到。
【讨论】：
currentPageIndex 来自哪里？
currentPageIndex 是您定义的本地变量，以便您可以跟踪当前页面。
如果有人想使用定义的协议来导航和以编程方式更改视图控制器，请把它留在这里。
@objc protocol AppWalkThroughDelegate {
@objc optional func goNextPage(forwardTo position: Int)
@objc optional func goPreviousPage(fowardTo position: Int)
}
使用上述协议并确认根 UIPageViewController 来管理视图控制器之间的导航。
下面的例子：
class AppWalkThroughViewController: UIPageViewController, UIPageViewControllerDataSource, AppWalkThroughDelegate {
// Add list of view controllers you want to load
var viewControllerList : [UIViewControllers] = {
let firstViewController = FirstViewController()
let secondViewController = SecondViewController()
// Assign root view controller as first responder
secondViewController.delegate = self
let thirdViewController = ThirdViewController()
}
override func viewDidLoad() {
super.viewDidLoad()
}
// Navigate to next page
func goNextPage(fowardTo position: Int) {
let viewController = self.viewControllerList[position]
setViewControllers([viewController], direction:
UIPageViewControllerNavigationDirection.forward, animated: true, completion: nil)
}
}
一旦实现了所有这些，需要使 UIPageViewController 移动到下一页或上一页的子视图控制器可以通过将特定数字传递给委托属性来使用 AppWalkThroughDelegate 方法。
以下示例：按下按钮后调用委托方法
class SecondViewController: UIViewController {
var delegate: AppWalkThroughDelegate!
override func viewDidLoad() {
super.viewDidLoad()
}
@IBAction func goNextPage(_ sender: Any) {
// Can be any number but not outside viewControllerList bounds
delegate.goNextPage!(fowardTo: 2)
}
}
【讨论】：