Question

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的工作原理如下。

当用户点击＆＃34;登录＆＃34;或＆＃34; SignUp＆＃34;按钮，它将分段到PageViewController
PageViewController将firstViewController设置为初始View
在PageViewController中，有3个方法是“getFirst”（获取firstViewController），“getSecond”（获取secondViewController），「getThird」（获取第三个ViewController）。

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）。

因此，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＆＃34; UIPageViewControllerDelegate＆＃34;并试图为左键调用「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”方法行中收到了此错误消息（对于右键，我可能会得到相同的错误）。

线程1：致命错误：在解包可选值时意外发现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？也许我无法以这种方式工作（我无法从其他文件中重用PageViewController？）。

请有人帮助我！

Answer 1

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toFirstTapped中，您实例化FirstViewController但不对其执行任何操作..

如果你什么都不做，你觉得它如何运作？

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，控制器就可以访问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，我更愿意跟踪数组中的控制器，并将其返回给我的代表。

如何使用现有UIPageViewController的按钮以编程方式滑动视图

1 个答案: