如何在Swift中关闭当前的ViewController并更改为新的ViewController？

Question

我是iOS Swift的新手。 我有三个ViewController。 页面A是根控制器，它将呈现给页面B。 在页面B中有一个计时器。 5秒钟后，它将视图从页面B更改为页面C，并同时关闭页面B。

在ViewControll-B

class AViewController: UIViewController {

    var timer: Timer?

    override func viewDidLoad() {
        super.viewDidLoad()

        //set the timer , and chagne view to C ViewController
        Timer.scheduledTimer(timeInterval: 5,
                             target: self,
                             selector: #selector(self.changeToAnswerView),
                             userInfo: nil,
                             repeats: false)
    }


    @objc func changeToAnswerView() {
        dismissLoader()
    }

    func dismissLoader() {
        dismiss(animated: true) {
            print("Dismissing Loader view Controller")
        }
    }

    override func viewWillDisappear(_ animated: Bool) {
        //change view to Answer ViewController
        let filterVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "CViewControllerID")
        filterVC.modalPresentationStyle = UIModalPresentationStyle.custom
        self.present(filterVC, animated: true, completion: nil)
    }

}

计时器执行5秒钟后， BViewController将关闭自身并呈现给BViewController 。

但是会发生以下错误：

whose view is not in the window hierarchy

我错过了什么吗？

问题： 如何在Swift中关闭当前的ViewController并更改为新的ViewController？

提前致谢。

Answer 1

这是您可以尝试的工作代码

您的控制器被解雇并倾向于制作一个新的控制器

import UIKit

class pdfVC: UIViewController
{

    var timer : Timer?

    override func viewDidLoad()
    {
        super.viewDidLoad()
        timer = Timer.scheduledTimer(timeInterval: 3, target: self, selector: #selector(pdfVC.timerAction), userInfo: nil, repeats: false)
    }

    @objc func timerAction()
    {
        if timer != nil {
            timer?.invalidate()
            dismiss(animated: true, completion: {
                print("Dismissed")
            })
        }
    }

    override func viewWillDisappear(_ animated: Bool) {
        if self.isBeingDismissed {
            let filterVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "demoViewController")
            filterVC.modalPresentationStyle = UIModalPresentationStyle.custom
            print("called")
            self.presentingViewController?.present(filterVC, animated: true, completion: nil)
        }
    }
}

输出量

Answer 2

您正在尝试使用视图控制器的引用（实例），该引用将不再存在于内存中。

尝试这个

if let presentingVC = self.presentingViewController {
        let filterVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "CViewControllerID")
        filterVC.modalPresentationStyle = UIModalPresentationStyle.custom
        presentingVC.present(filterVC, animated: true, completion: nil)
}

注意：关闭当前视图控制器后，请提供一个新的视图控制器（filterVC）。 一个视图控制器一次只能显示一个视图控制器（如果您选择模态显示）。 延迟1秒后执行此操作。

编辑

尝试使用此编辑后的代码。

Class AViewController: UIViewController {

    var timer: Timer?
    var presentingVC: UIViewController?
    override func viewDidLoad() {
        super.viewDidLoad()

        //set the timer , and chagne view to C ViewController
        Timer.scheduledTimer(timeInterval: 5,
                             target: self,
                             selector: #selector(self.changeToAnswerView),
                             userInfo: nil,
                             repeats: false)
    }


    @objc func changeToAnswerView() {
        dismissLoader()
    }

    func dismissLoader() {
        dismiss(animated: true) {
            print("Dismissing Loader view Controller")
        }
    }

    override func viewDidAppear(_ animated: Bool) {
         super.viewDidAppear(animated)
        //change view to Answer ViewController
        if let presentingVC = self.presentingViewController {
           self.presentingVC = presentingVC
        }
    }

    override func viewWillDisappear(_ animated: Bool) {
        //change view to Answer ViewController
        super.viewWillDisappear(animated)
       if let presentingVC = self.presentingVC {

        let filterVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "CViewControllerID")
        filterVC.modalPresentationStyle = UIModalPresentationStyle.custom
        presentingVC?.present(filterVC, animated: true, completion: nil)

      } else {
         print("Presenting View controller is nil")
      }
    }

}

Answer 3

尝试将dismissLoader函数更改为以下内容：

func dismissLoader() {
    dismiss(animated: true) {
        print("Dismissing Loader view Controller")
        if let presentingController = self.presentingViewController {
            let filterVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "BViewControllerID")
            filterVC.modalPresentationStyle = UIModalPresentationStyle.custom
            presentingController.present(filterVC, animated: true, completion: nil)
        }
    }
}

并删除viewWillDisappear函数。

问题是您正在尝试将BViewController从被解雇（即从窗口层次结构中删除）之后的加载器中呈现出来，那时该视图不存在。

因此，解决方案是您可以获得对呈现视图控制器的引用，该视图控制器正在呈现加载器，并且在解除加载器并从此处呈现新视图控制器后将出现该视图控制器。

Answer 4

在您的B视图控制器被解雇后，在其完成处理程序中

 self.dismiss(animated: true) {
     if let presentingVC = self.presentingViewController {
        present c view controller here
     }
 }

以上是这样做的一种方法，另一种方法是通过委托

在视图控制器中：

if let bVC = self.storyboard.instantiateViewController(withIdentifier: B.controllerIdentifier) as? B  {

        bVC.delegate = self
        self.present(bVC, animated: true, completion: nil)
    }

内部B View Controller

为协议添加委托方法

protocol BProtocol: class {
    func didClose()
}

并在B中解雇

 var delegate:  BProtocol?
self.dismiss(animated: true) {
     self.delegate?.didClose()
 }

此委托将由ViewController实现为

extension AViewController: BProtocol {
    func didClose() {
        //present C
    }
}