尝试在已经呈现的View Controller上呈现UIAlertController(null)[Swift]

Question

我有一个警报视图,我试图在照片视图上呈现.

照片显示在列表中,可以推送到全屏视图.

照片视图以编程方式显示.我认为这是导致问题的原因,因为警报视图试图在已经呈现的(照片)视图之上呈现另一个视图.

警报视图正在尝试显示,但是收到此错误:

Warning: Attempt to present <UIAlertController: 0x147d2c6b0>  on <LiveDeadApp.ListViewController: 0x147d614c0> which is already presenting (null)

可能有问题的一行是这一行:

 self.present(textPrompt, animated: true, completion: nil)

这是主列表视图

这是截屏时的主要列表视图

这是主要的照片视图

这是主照片视图中的弹出窗口(通过"i"按钮访问)

在主照片视图上拍摄屏幕截图时,不会发生警报视图.但是,当设备的方向发生变化时,照片视图会返回列表并显示警报.

这就是我想要做的:

iOS 10中的Swift 3

谢谢!

这是列表视图和照片视图的代码:

import UIKit
import Kingfisher
import SKPhotoBrowser

class ListViewCell: UITableViewCell {

@IBOutlet weak var Cellimage: UIImageView!

@IBOutlet weak var cellVenue: UILabel!

@IBOutlet weak var cellLocation: UILabel!

@IBOutlet weak var cellDate: UILabel!
@IBOutlet weak var aiView: UIActivityIndicatorView!
}

class ListViewController: UITableViewController {

var subcategory:Subcategory!

var objects:[[String:String]] = [[String:String]]()

var images = [SKPhotoProtocol]()



override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)


}

override func viewDidLoad() {
    super.viewDidLoad()


    self.tableView.separatorStyle = .none

    self.view.backgroundColor = UIColor.black

    self.navigationController?.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName: UIColor.white]

    navigationController!.navigationBar.barTintColor = UIColor.black

    let requireTextInput = "require text input"
    // add observer for screen shot
    NotificationCenter.default.addObserver(forName: NSNotification.Name.UIApplicationUserDidTakeScreenshot, object: nil, queue: OperationQueue.main, using:
        { notification in

            self.definesPresentationContext = true

            var inputTextField = UITextField()

            let textPrompt = UIAlertController(title: "Test!", message: "Testing!", preferredStyle: .alert)

            textPrompt.addAction(UIAlertAction(title: "Continue", style: .default, handler: {
                (action) -> Void in
                // if the input match the required text

                let str = inputTextField.text
                if str == requireTextInput {
                    print("right")
                } else {
                    print("wrong")
                }

            }))

            textPrompt.addTextField(configurationHandler: {(textField: UITextField!) in
                textField.placeholder = ""
                inputTextField = textField

            })

            self.present(textPrompt, animated: true, completion: nil)

    })

    if subcategory != nil {
        self.title = subcategory.title
        self.objects = subcategory.photos

        createLocalPhotos()

        self.tableView.reloadData()
    }


}

func createLocalPhotos() {

    for item in objects {
        let photo = SKPhoto.photoWithImageURL(item["url"]!)
        photo.shouldCachePhotoURLImage = true
        images.append(photo)
    }

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}

override func numberOfSections(in tableView: UITableView) -> Int {
    return 1
}

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return objects.count
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cell: ListViewCell = tableView.dequeueReusableCell(withIdentifier: "Cell") as! ListViewCell

    let item = objects[indexPath.row]

    let title = item["title"]
    let location = item["location"]
    let date = item["date"]
    let urlSrt = item["url"]


    cell.cellVenue.text = title
    cell.cellLocation.text = location
    cell.cellDate.text = date

    if let url = URL(string: urlSrt!) {
        cell.aiView.startAnimating()
        cell.Cellimage.kf.setImage(with: url, placeholder: nil, options: nil, progressBlock: nil, completionHandler: { (image, error, cacheType, url) in
            cell.aiView.stopAnimating()
        })
    }

    return cell

}

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let cell = tableView.cellForRow(at: indexPath) as! ListViewCell

    if(cell.Cellimage.image != nil ) {
        SKPhotoBrowserOptions.displayToolbar = false
        SKPhotoBrowserOptions.displayCounterLabel = false
        SKPhotoBrowserOptions.displayBackAndForwardButton = false
        SKPhotoBrowserOptions.displayAction = false
        SKPhotoBrowserOptions.displayDeleteButton = true
        SKPhotoBrowserOptions.displayHorizontalScrollIndicator = false
        SKPhotoBrowserOptions.displayVerticalScrollIndicator = false
        SKPhotoBrowserOptions.displayStatusbar = false
        SKPhotoBrowserOptions.disableVerticalSwipe = true
        SKPhotoBrowserOptions.bounceAnimation = false
        let browser = ExtendedSKPhotoBrowser(originImage: cell.Cellimage.image!, photos: images, animatedFromView: cell)

        let btnSize = 80//24 * UIScreen.main.scale

        browser.updateCloseButton(UIImage(named: "ic_close_white")!, size: CGSize(width: btnSize, height: btnSize))
        browser.updateDeleteButton(UIImage(named: "ic_info_white")!, size: CGSize(width: btnSize, height: btnSize))
        browser.initializePageIndex(indexPath.row)
        browser.delegate = self
        present(browser, animated: true, completion: {})
        browser.toggleControls()
    }
}

override var prefersStatusBarHidden: Bool {
    get {
        return true
    }
}


var popOverVC:PopUpViewController!
}

extension ListViewController: SKPhotoBrowserDelegate {
func didShowPhotoAtIndex(_ index: Int) {






}

func willDismissAtPageIndex(_ index: Int) {

}

private func willShowActionSheet(photoIndex: Int) {
    // do some handle if you need
}

func didDismissAtPageIndex(_ index: Int) {
}

func didDismissActionSheetWithButtonIndex(_ buttonIndex: Int, photoIndex: Int) {
    // handle dismissing custom actions
}

func removePhoto(_ browser: SKPhotoBrowser, index: Int, reload: (() -> Void)) {
    popOverVC = self.storyboard?.instantiateViewController(withIdentifier: "sbPopUpID") as! PopUpViewController
    popOverVC.photoData = objects[index]

}

func viewForPhoto(_ browser: SKPhotoBrowser, index: Int) -> UIView? {
    return tableView.cellForRow(at: IndexPath(row: index, section: 0))
}
}


open class ExtendedSKPhotoBrowser: SKPhotoBrowser {

open override var preferredStatusBarStyle: UIStatusBarStyle {
    return .lightContent // white statusbar, .default is black
}

open override var prefersStatusBarHidden: Bool {
    return true
}
}

Answer 1

问题确实很简单，您正在尝试UIAlertController在当前显示的上显示另一个UIAlertController。

那么，如何解决这种情况呢？

1. 您需要获取UIAlertController当前视图控制器中使用的所有列表。

2. 您必须检查在当前视图控制器（或其他视图控制器（如果正在执行异步请求）中）显示警报的逻辑。

3. 当您要在另一个警报上显示一个警报时，您的代码必须像这样。

假设loadingAlert当前正在屏幕上显示：

self.loadingAlert.dismiss(animated: true, completion: {
     let anotherAlert = UIAlertController(title: "New One", message: "The Previous one is dismissed", preferredStyle: .alert)
     let okAction = UIAlertAction(title: "OK", style: .default, handler: nil)
     anotherAlert.addAction(okAction)
     self.present(anotherAlert, animated: true, completion: nil)
})

您必须先消除第一个，然后才能显示下一个。我之所以做出这样的回答，是为了消除没有按钮的警报，从而提高警报效率。

那么，带有操作按钮的警报呢？

当您单击UIAlertController创建的动作按钮之一时，它将自动关闭。

但是，如果同时显示两个UIAlertController包含UIButton的，则问题仍然会发生。您需要重新检查每个逻辑，或者可以在处理程序中为每个操作处理逻辑：

self.connectionErrorAlert.dismiss(animated: true, completion: {
     let anotherAlert = UIAlertController(title: "New One", message: "The Previous one is dismissed", preferredStyle: .alert)
     let okAction = UIAlertAction(title: "OK", style: .default, handler: {action in
            let nextAlert = UIAlertController(title: "New One", message: "The Previous one is dismissed", preferredStyle: .alert)
            self.present(nextAlert, animated: true, completion: nil)
     })
     anotherAlert.addAction(okAction)
     self.present(anotherAlert, animated: true, completion: nil)
})

对于迈克的答案：

DispatchQueue.main.async(execute: {

      if self.presentedViewController == nil {
           print("Alert comes up with the intended ViewController")
           var inputTextField = UITextField()

           let textPrompt = UIAlertController(title: "Test", message: "Testing", preferredStyle: .alert)

           textPrompt.addAction(UIAlertAction(title: "Continue", style: .default, handler: {
               (action) -> Void in
               // if the input matches the required text

               let str = inputTextField.text
               if str == requireTextInput {
                    print("right")
               } else {
                    print("wrong")
               }

           }))

           textPrompt.addTextField(configurationHandler: {(textField: UITextField!) in
                textField.placeholder = ""
                inputTextField = textField

            })
            weakSelf?.present(textPrompt, animated: true, completion: nil)
      } else {
            // either the Alert is already presented, or any other view controller
            // is active (e.g. a PopOver)
            // ...
            let thePresentedVC : UIViewController? = self.presentedViewController as UIViewController?
            if thePresentedVC != nil {
                 if let _ : UIAlertController = thePresentedVC as? UIAlertController {
                      print("Alert not necessary, already on the screen !")

              } else {

                      print("Alert comes up via another presented VC, e.g. a PopOver")
              }
            }
       }
})

感谢@Luke答案：https ://stackoverflow.com/a/30741496/3378606

Answer 2

Hy，我尝试了一个更简单的解决方案，该解决方案似乎有效，并且能够在第一个警报之前显示第二个警报，该警报将保留（在用户回答问题之前无需关闭）：

if self.presentedViewController==nil{
    self.present(MyAlert, animated: true, completion: nil)
}else{
    self.presentedViewController!.present(MyAlert, animated: true, completion: nil)
}