我正在开发一个具有3个主要视图的应用程序，为了让用户只需轻扫即可更改3个视图（如Tinder应用程序），我创建了一个PageViewController，它运行良好。这个PageViewController的工作方式如下。
我还在每个3个视图的上方添加了按钮，并希望用户能够点击这些按钮滑动到其他视图，就像它们滑动那些视图时一样（这也像Tinder）。
所以对于实验，我在SecondViewController上添加了两个按钮。左边是移动到FirstViewController，右边是移动到ThirdViewController。然后，在SecondViewController文件中，我添加了“UIPageViewControllerDelegate”并尝试为左键调用“getFirst”方法，并从PageViewController文件中调用右键的“getThird”方法。
但是当我点击左键时，我在PageViewController文件的“getFirst”方法行上得到了这条错误消息（对于右键，我可能会得到相同的错误）。
线程1：致命错误：在解开Optional值时意外发现nil
代码如下。
PageViewController
import UIKit
class PageViewController: UIPageViewController {
override func viewDidLoad() {
super.viewDidLoad()
self.setViewControllers([getFirst()], direction: .forward, animated: true, completion: nil)
self.dataSource = self as UIPageViewControllerDataSource
}
}
extension PageViewController : UIPageViewControllerDataSource {
//FirstViewController
@objc func getFirst() -> FirstViewController {
return storyboard!.instantiateViewController(withIdentifier: "FirstViewController") as! FirstViewController
}
//SecondViewController
@objc func getSecond() -> SecondViewController {
return storyboard!.instantiateViewController(withIdentifier: "SecondViewController") as! SecondViewController
}
//ThirdViewController
@objc func getThird() -> ThirdViewController {
return storyboard!.instantiateViewController(withIdentifier: "ThirdViewController") as! ThirdViewController
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
if viewController.isKind(of: ThirdViewController.self) {
// 3 -> 2
return getSecond()
} else if viewController.isKind(of: SecondViewController.self) {
// 2 -> 1
return getFirst()
} else {
// 1 -> end of the road
return nil
}
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
if viewController.isKind(of: FirstViewController.self) {
// 1 -> 2
return getSecond()
} else if viewController.isKind(of: SecondViewController.self) {
// 2 -> 3
return getThird()
} else {
// 3 -> end of the road
return nil
}
}
}
SecondViewController
import UIKit
class SecondViewController: UIViewController, UIPageViewControllerDelegate {
let pageHelper = PageViewController()
override func viewDidLoad() {
super.viewDidLoad()
pageHelper.delegate = self
}
@IBAction func toFirstTapped(_ sender: Any) {
pageHelper.getFirst()
}
}
我错过了什么？也许我不能让它以这种方式工作（我不能从其他文件中重用PageViewController？）。
请有人帮帮我！
首先，PageViewController实例化一个实例化PageViewController的子控制器..这真的是个好主意吗？然后在你的toFirstTapped，你实例化一个FirstViewController，但没有做任何事情..
如果你什么都不做，你怎么期望它的工作？
无论如何，请尝试以下方法：
protocol PageNavigationDelegate : class {
weak var pageController: PageViewController? { get set }
}
class PageViewController: UIPageViewController {
override func viewDidLoad() {
super.viewDidLoad()
self.setViewControllers([getFirst()], direction: .forward, animated: true, completion: nil)
self.dataSource = self as UIPageViewControllerDataSource
}
}
extension PageViewController : UIPageViewControllerDataSource {
func getFirst() -> FirstViewController {
let controller = storyboard!.instantiateViewController(withIdentifier: "FirstViewController") as! FirstViewController
controller.pageController = self
return controller
}
func getSecond() -> SecondViewController {
let controller = storyboard!.instantiateViewController(withIdentifier: "SecondViewController") as! SecondViewController
controller.pageController = self
return controller
}
func getThird() -> ThirdViewController {
let controller = storyboard!.instantiateViewController(withIdentifier: "ThirdViewController") as! ThirdViewController
controller.pageController = self
return controller
}
@discardableResult
func goToPreviousPage() -> Bool {
let controller = self.viewControllers!.first!
if controller.isKind(of: SecondViewController.self) {
self.setViewControllers([getFirst()], direction: .reverse, animated: true, completion: nil)
return true
}
if controller.isKind(of: ThirdViewController.self) {
self.setViewControllers([getSecond()], direction: .reverse, animated: true, completion: nil)
return true
}
return false
}
@discardableResult
func goToNextPage() -> Bool {
let controller = self.viewControllers!.first!
if controller.isKind(of: FirstViewController.self) {
self.setViewControllers([getSecond()], direction: .forward, animated: true, completion: nil)
return true
}
if controller.isKind(of: SecondViewController.self) {
self.setViewControllers([getThird()], direction: .forward, animated: true, completion: nil)
return true
}
return false
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
if viewController.isKind(of: SecondViewController.self) {
return getFirst()
}
if viewController.isKind(of: ThirdViewController.self) {
return getSecond()
}
return nil
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
if viewController.isKind(of: FirstViewController.self) {
return getSecond()
}
if viewController.isKind(of: SecondViewController.self) {
return getThird()
}
return nil
}
}
class PageNavigationController : UIViewController, PageNavigationDelegate {
var pageController: PageViewController?
override func viewDidLoad() {
super.viewDidLoad()
}
@IBAction func goToPreviousController(_ sender: Any) {
pageController?.goToPreviousPage()
}
@IBAction func goToNextController(_ sender: Any) {
pageController?.goToNextPage()
}
}
class FirstViewController: PageNavigationController {
}
class SecondViewController: PageNavigationController {
}
class ThirdViewController: PageNavigationController {
}
首先我们创建了一个协议。我们确保所有PageController的子控制器都将实现它。这样，他们就可以导航到上一页和下一页。
接下来，我们创建具有goToPreviousPage和goToNextPage函数的扩展。当我们实例化每个控制器页面时，我们将self分配给它的协议实现变量。这样，控制器可以访问PageViewController的方法..
最后，在我们的First，Second和Third控制器中，我们只是告诉它按下按钮前进或后退。
就个人而言，我更喜欢跟踪数组中的控制器，并只返回我的代表中的控制器。