Ios 尝试在已呈现的视图控制器上呈现UIAlertController（null）[Swift]

我有一个警报视图，我正试图在照片视图中显示

照片显示在列表中，可以推送到全屏视图

正在以编程方式显示照片视图。我认为这就是问题的原因，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

警报视图正试图显示，但出现以下错误：

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

<pre><code>    
@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIButton *btn1;
@property (weak, nonatomic) IBOutlet UIButton *btn2;
@end

@implementation ViewController

- (void)viewDidLoad {
   [super viewDidLoad];
}

- (IBAction)btn1:(id)sender {
   UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Btn1"
                   message:@"This is Btn1." preferredStyle:UIAlertControllerStyleAlert];

   UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * action) {}];

   [alert addAction:defaultAction];
   [self presentViewController:alert animated:YES completion:nil];
}

- (IBAction)btn2:(id)sender {
   UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Btn2"
                     message:@"This is Btn2." preferredStyle:UIAlertControllerStyleAlert];

   UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * action) {}];

   [alert addAction:defaultAction];
   [self presentViewController:alert animated:YES completion:nil];
}
</code></pre>

这是主列表视图

这是拍摄屏幕截图时的主列表视图

这是主要的照片视图

这是主照片视图中的弹出框（通过“i”按钮访问）

在主照片视图上拍摄屏幕截图时，不会出现警告视图。但是，当设备的方向改变时，照片视图返回列表并显示警报。

这就是我要做的：

iOS 10中的Swift 3

谢谢大家!

以下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
}
}

在ViewDidLoad中，
使

弱

变量，如

弱var weakSelf=self

在通知中心，
呈现

textPropmt

类似

weak var weakSelf = self
NotificationCenter.default.addObserver(forName: NSNotification.Name.UIApplicationUserDidTakeScreenshot, object: nil, queue: OperationQueue.main, using:
        { notification in
 DispatchQueue.main.async(execute: {
  //create textPrompt here in Main Thread
  weakSelf.present(textPrompt, animated: true, completion: nil)
 })
})

---

问题很简单，您正试图在当前显示的

UIAlertController

上显示另一个

UIAlertController

那么，如何解决这种情况呢

您需要获取当前视图控制器中使用的所有

UIAlertController

的列表。

您必须检查当前视图控制器（或其他视图控制器，如果您正在执行异步请求）中显示警报的逻辑。

如果要在一个警报上显示另一个警报，则代码必须如下所示。

假设loadingAlert当前显示在屏幕上：

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)
})

在下一个出现之前，您必须先关闭第一个。我之所以这样回答是因为我拒绝了一个没有按钮的警报，以提高它的效率

那么，带操作按钮的警报呢？

当您单击其中一个操作时，它将自动关闭 您创建的

UIAlertController

上的按钮

但是，如果同时显示两个包含

ui按钮的
ui警报控制器
s，则问题仍然会发生。您需要重新检查每个操作的逻辑，或者可以在每个操作的处理程序中处理它：

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)
})

要回答迈克的问题：

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 Answer:

在我的情况下，我无法将我的放在类重写中。下面是我得到的：

let viewController = self // I had viewController passed in as a function,
                          // but otherwise you can do this


// Present the view controller
let currentViewController = UIApplication.shared.keyWindow?.rootViewController
currentViewController?.dismiss(animated: true, completion: nil)

if viewController.presentedViewController == nil {
    currentViewController?.present(alert, animated: true, completion: nil)
} else {
    viewController.present(alert, animated: true, completion: nil)
}

我受了这个问题的折磨，一直到现在。这是一个简单的应用程序，上面有两个按钮。点击第一个按钮会导致“2019-03-05 16:58:04.094541-0500 ReadJason[41100:1610082]警告：尝试呈现已呈现的内容”错误

将按钮2复制为按钮1导致此问题。每个按钮都绑定到一个动作（btn1和btn2）。当我复制btn2来制作btn1时，btn2的连接包含在btn1的代码中。然后，我将连接添加到btn1，这导致两个发送事件连接到btn1，这就是导致错误的原因

检查按钮1的事件将显示两个操作：。删除不需要的操作将清除错误

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

---

我相信，您需要确保是否已经有另一个AlerViewController试图在ViewController上表示自己

---

至少这是我的问题。

我是否应该将警报视图的所有代码放在主线程的“//create textPrompt”中？谢谢你的回复！这就是为什么我在代码中添加了该注释，去吧，好的，对不起。仍然得到错误，没有弹出窗口。必须在“weakSelf”之后添加“？”。仅当您尝试呈现已呈现的控制器（或呈现的任何其他控制器）时，才会出现此错误。检查您是否在代码中的某个地方两次显示“UIAlertController”。@KrishnaDattShukla这是我唯一显示警报控制器的地方。不过，我也在演示一个popover控制器。我认为您同时演示了popover和alert。这就是产生此错误的原因。解除popover后，请出示您的警报控制器。@KrishnaDattShukla我不确定如何执行此操作。我已经在我的问题中添加了一些照片以供澄清。非常感谢你！谢谢你的全面回复。我仍然不确定如何着手做这件事。我已经在我的问题中添加了一些照片以供澄清。非常感谢。您当前的问题中有多少控制器？只有一个listViewController？只有一个：listViewController。如果我没记错的话，您正在listViewController中显示照片（1,2,3）。单击其中一个按钮时，将显示详细信息（假设1）。当您单击信息（i）时，弹出窗口会出现，当您单击“添加到Fav”时，会出现警报。我说的对吗？除了“添加到Fav”部分外，这是正确的。“添加到Fav”与此问题是分开的。拍摄屏幕截图时会出现此警报。这是一个优雅的简单解决方案，但您最好检查presentedViewController！=事先通知视图控制器。

<pre><code>    
@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIButton *btn1;
@property (weak, nonatomic) IBOutlet UIButton *btn2;
@end

@implementation ViewController

- (void)viewDidLoad {
   [super viewDidLoad];
}

- (IBAction)btn1:(id)sender {
   UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Btn1"
                   message:@"This is Btn1." preferredStyle:UIAlertControllerStyleAlert];

   UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * action) {}];

   [alert addAction:defaultAction];
   [self presentViewController:alert animated:YES completion:nil];
}

- (IBAction)btn2:(id)sender {
   UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Btn2"
                     message:@"This is Btn2." preferredStyle:UIAlertControllerStyleAlert];

   UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * action) {}];

   [alert addAction:defaultAction];
   [self presentViewController:alert animated:YES completion:nil];
}
</code></pre>

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