Swift - 在 UIPageViewController 中的 3 个不同视图控制器之间导航按钮

Question

所以我一直在尝试 UIPageViewController，我有三个不同的视图控制器（3 个不同的类）

所以我成功了！我可以完美地从 View Controller 滑动到 View Controller！在这三个类的 viewDidLoad 中，我分别设置了它们的 self.view.tag = 0,1,2，所以我知道我当前的 View Controller 是哪个。这是我的 RootViewController 的代码：

import UIKit

class ViewController: UIViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {
@IBOutlet var bottomView: UIView!

var pageViewController: UIPageViewController!
var currentVCId = 0

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    pageViewController = self.storyboard?.instantiateViewController(withIdentifier: "PageViewController") as! UIPageViewController
    pageViewController.dataSource = self
    pageViewController.delegate = self

    let starterVC = viewControllerWith(id: 0)

    pageViewController.setViewControllers([starterVC], direction: .forward, animated: false, completion: nil)
    pageViewController.view.frame = CGRect(x: 0, y: 0, width: self.view.frame.width, height: self.view.frame.height)

    self.addChildViewController(pageViewController)
    self.view.addSubview(pageViewController.view)
    self.view.bringSubview(toFront: bottomView)

    pageViewController.didMove(toParentViewController: self)
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

func viewControllerWith(id: Int) -> UIViewController {
    if id == 0 {
        return self.storyboard?.instantiateViewController(withIdentifier: "FirstPageContentViewController") as! FirstPageContentViewController
    }
    else if id == 1 {
        return self.storyboard?.instantiateViewController(withIdentifier: "SecondPageContentViewController") as! SecondPageContentViewController
    }
    else {
        return self.storyboard?.instantiateViewController(withIdentifier: "RandomColorViewController") as! RandomColorViewController
    }
}

func getViewControllerIdFor(previousViewController: Bool) -> Int? {
    if previousViewController == true {
        return currentVCId == 0 ? nil : currentVCId - 1
    }

    return currentVCId == 2 ? nil : currentVCId + 1
}

func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
    if let returnIdValue = getViewControllerIdFor(previousViewController: true) {
        return viewControllerWith(id: returnIdValue)
    }

    return nil
}

func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
    if let returnIdValue = getViewControllerIdFor(previousViewController: false) {
        return viewControllerWith(id: returnIdValue)
    }

    return nil
}

func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
    guard completed else {
        return
    }

    let viewController = pageViewController.viewControllers![0]
    currentVCId = viewController.view.tag
}

@IBAction func goToA(_ sender: UIButton) {
    if currentVCId != 0 {
        let currentVC = pageViewController.viewControllers?[0]
        let previusVC = pageViewController(pageViewController, viewControllerBefore: currentVC!)

        pageViewController.setViewControllers([previusVC!], direction: .reverse, animated: true, completion: nil)
        currentVCId = 0
    }
}

}

问题是，我在 RootViewController 中添加了 2 个按钮，无需滑动即可从视图控制器切换到视图控制器。所以，假设我已经滑动到第二个视图控制器并且我想返回我的第一个，按左键.. 记住我的第一个 VC 已经加载，所以我可以修改它的内容..

所以现在，如果我按下按钮，它的代码是上面的最后一个方法，它会导航回来，但它会创建所需 VC 的新实例！我想要做的，是展示我已经加载的VC，就好像我在刷卡一样……就像Snapchat一样……

你知道如何实现吗？

Answer 1

这是来自instantiateViewController(withIdentifier:)上的documentation

此方法在您每次调用时都会创建指定视图控制器的新实例。

这就是您获得新实例的原因。我会推荐一种不同的方法。与其让 pageViewController 跟踪 VC 并通过索引和标签盲目地访问它们，为什么不将它们作为属性存储在您的根目录中呢？这将允许您确保 VC 的相同实例，并且可以让您从检查标签（这是脏的）转移到更易读的东西，例如检查与实际 VC 对象的相等性。