在强制展开可选的 swift 2 时发现 nil

Posted 2023-02-27

【中文标题】在强制展开可选的 swift 2 时发现 nil

【英文标题】：Found nil while force unwrapping an optional swift 2

【发布时间】：2015-11-27 15:07:41

【问题描述】：

我在展开可选值时不断收到错误消息，提示发现 nil。我不知道为什么会这样做，因为数据是从另一个视图控制器存储到变量中的，但它没有分配新值，而是将其保持为零。为什么要这样做？任何帮助将不胜感激。

注意：它在 userEventViewController 的第 47 行崩溃

在线崩溃：myTitle.title = event!.name

项目链接：https://www.dropbox.com/s/1d4d8opuxzpcuk4/TicketekApp.zip?dl=0

代码：

源视图控制器（EventTableViewController）：

//  EventTableViewController.swift



import UIKit

class EventTableViewController: UITableViewController 
// MARK: Properties
var currentlySelectedIndex = 0
var events = [Event]()
var isAdmin: Bool = false
var currentUser: String = ""
override func viewDidLoad() 
    super.viewDidLoad()
    print(currentUser)
    // Use the edit button item provided by the table view controller.
    if isAdmin == true 
    navigationItem.leftBarButtonItem = editButtonItem()
    
    // Load any saved events, otherwise load sample data.
    if let savedEvents = loadEvents() 
        events += savedEvents
     else 
        // Load the sample data.
        loadSampleEvents()
    


func loadSampleEvents() 
    let photo1 = UIImage(named: "event1")!
    let event1 = Event(name: "ACDC", photo: photo1, rating: 4, price: 100.0, eventDescription: "AC/DC are an Australian hard rock band, formed in November 1973 by brothers Malcolm and Angus Young, who continued as members until Malcolm's illness and departure in 2014. Date of Event: 1/3/16", album: "Redemption Tour")!

    let photo2 = UIImage(named: "event2")!
    let event2 = Event(name: "Cold Play", photo: photo2, rating: 5, price: 150.0, eventDescription: "Coldplay are a British rock band formed in 1996 by lead vocalist Chris Martin and lead guitarist Jonny Buckland at University College London. Date of Event: 12/12/15", album: "Mylo Xyloto")!

    let photo3 = UIImage(named: "event3")!
    let event3 = Event(name: "One Direction", photo: photo3, rating: 3, price: 120.0, eventDescription: "One Direction are an English-Irish pop boy band based in London, composed of Niall Horan, Liam Payne, Harry Styles, Louis Tomlinson, and previously, Zayn Malik until his departure from the band on 25 March 2015. Date of Event: 5/9/16", album: "Made in the A.M.")!

    events += [event1, event2, event3]


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


// MARK: - Table view data source

override func numberOfSectionsInTableView(tableView: UITableView) -> Int 
    return 1


override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int 
    return events.count


override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell 
    // Table view cells are reused and should be dequeued using a cell identifier.
    let cellIdentifier = "EventTableViewCell"
    let cell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier, forIndexPath: indexPath) as! EventTableViewCell

    // Fetches the appropriate event for the data source layout.
    let event = events[indexPath.row]

    cell.nameLabel.text = event.name
    cell.photoImageView.image = event.photo
    cell.ratingControl.rating = event.rating
    cell.priceLabel.text = event.album

    return cell

override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) 

    //Record the row selected
    currentlySelectedIndex = indexPath.row

    //check for admin
    if isAdmin == true 
        performSegueWithIdentifier("eventViewControllerSegue", sender: self)
     else 
        performSegueWithIdentifier("userEventViewControllerSegue", sender: self)
    


// Override to support conditional editing of the table view.
override func tableView(tableView: UITableView, canEditRowAtIndexPath indexPath: NSIndexPath) -> Bool 
    // Return false if you do not want item to be editable.
    if isAdmin == true 
    return true
     else 
        return false
    



// Override to support editing the table view.
override func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) 
    if isAdmin == true 
    if editingStyle == .Delete 
        // Delete the row from the data source
        events.removeAtIndex(indexPath.row)
        saveEvents()
        tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
     else if editingStyle == .Insert 
        // Create new instance of  class, add to the array, and add a new row to the table
    
    



/*
// Override to support rearranging the table view.
override func tableView(tableView: UITableView, moveRowAtIndexPath fromIndexPath: NSIndexPath, toIndexPath: NSIndexPath) 


*/


// Override to support conditional rearranging of the table view.
override func tableView(tableView: UITableView, canMoveRowAtIndexPath indexPath: NSIndexPath) -> Bool 
// Return false if you do not want the item to be re-orderable.
    if isAdmin == true 
return true
     else 
        return false
    




// MARK: - Navigation

// preparation before navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) 
    if segue.identifier == "eventViewControllerSegue"  
        let destinationVC1 = segue.destinationViewController as? EventViewController
        destinationVC1!.event = events[currentlySelectedIndex]
     else  if segue.identifier == "userEventViewControllerSegue"  
        let eventDetailViewController = segue.destinationViewController as! UserEventViewController
        //Get the associated event
        eventDetailViewController.event = events[currentlySelectedIndex]
        let destinationVC = segue.destinationViewController as? UserEventViewController
            destinationVC!.event = events[currentlySelectedIndex]
            destinationVC!.currentUser = currentUser

    
    else if segue.identifier == "AddItem" 
        print("Adding new event.")
    


@IBAction func unwindToMealList(sender: UIStoryboardSegue) 
    if let sourceViewController = sender.sourceViewController as? EventViewController, event = sourceViewController.event 
        if let selectedIndexPath = tableView.indexPathForSelectedRow 
            // Update an existing event.
            events[selectedIndexPath.row] = event
            tableView.reloadRowsAtIndexPaths([selectedIndexPath], withRowAnimation: .None)
         else 
            // Add a new event.
            let newIndexPath = NSIndexPath(forRow: events.count, inSection: 0)
            events.append(event)
            tableView.insertRowsAtIndexPaths([newIndexPath], withRowAnimation: .Bottom)
        
        // Save the events.
        saveEvents()
    


// MARK: NSCoding

func saveEvents() 
    let isSuccessfulSave = NSKeyedArchiver.archiveRootObject(events, toFile: Event.ArchiveURL.path!)
    if !isSuccessfulSave 
        print("Failed to save events...")
    


func loadEvents() -> [Event]? 
    return NSKeyedUnarchiver.unarchiveObjectWithFile(Event.ArchiveURL.path!) as? [Event]

目标视图控制器（userEventViewController）：

//  EventViewController.swift



import UIKit

class UserEventViewController: UIViewController 
// MARK: Properties










@IBOutlet weak var eventDescriptionLabel: UITextView!

@IBOutlet weak var priceLabel: UILabel!

@IBOutlet weak var nameLabel: UILabel!

@IBOutlet weak var photoImageView: UIImageView!

@IBOutlet weak var albumNameLabel: UILabel!

@IBOutlet weak var myTitle: UINavigationItem!

@IBOutlet weak var ratingControl: RatingControl!

var event: Event?
var currentUser: String = ""





override func viewDidLoad() 
    super.viewDidLoad()


    // Set up views if editing an existing event.
    //                        |
    // Crashes on this line  \./
        myTitle.title = event!.name
        nameLabel.text   = event!.name
        photoImageView.image = event!.photo
        ratingControl.rating = event!.rating
        eventDescriptionLabel.text = event!.eventDescription
        albumNameLabel.text = event!.album
        priceLabel.text = String(event!.price)
        print(currentUser)

    



@IBAction func buyTickets(sender: AnyObject) 
    performSegueWithIdentifier("BuyTickets", sender: self)




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

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) 
    if segue.identifier == "BuyTickets" 
        let destinationVC = segue.destinationViewController as? seatsPickerViewController
            destinationVC!.price = event!.price
            destinationVC!.name = event!.name
            destinationVC!.album = event!.album
            destinationVC!.photo = event!.photo
            destinationVC!.currentUser = currentUser

                

【问题讨论】：

在哪一行崩溃？

userEventViewController @luk2302 第 47 行

好吧，要么在源代码中包含行号（不推荐），要么告诉我们行，而不是行号，我应该如何计算 8 个空白连续几行？

抱歉，添加到@luk2302

尝试删除处理destinationVC的三行

【参考方案1】：

您尚未连接插座：

【参考方案2】：

它会崩溃，因为你还没有初始化event。你刚刚声明它是一个可选的，所以当你选择在几行之后打开它时它保持为零。我们知道，如果你试图解开 nil，你的程序就会崩溃。

给event赋值然后试试