Swift - self.navigationController在转换后变为nil

Question

我在我的应用程序中遇到一个非常奇怪的错误,在两个视图之间,self.navigationController正在变为nil

我有几个视图控制器:MainViewController,SecondViewController PastSessionsViewController,JournalViewController.我使用JournalViewController两个目的,将新条目保存到CoreData或编辑较旧的条目.详细信息与此错误无关.

当我尝试弹出JournalViewController堆栈并返回MainViewController但仅在JournalViewController处于"编辑"模式时,而不是在"保存新的输入模式"时,会发生错误

任何想法1)为什么会发生这种情况2)如何正确地解决它,以便我可以在编辑模式下返回PastSessionsViewController时返回JournalViewController？

这里有一些代码可以使事情具体化.

在AppDelegate.swift(里面didFinishLaunchingWithOptions):

navController = UINavigationController()

navController!.navigationBarHidden = true
var viewController = MainViewController()
navController!.pushViewController(viewController, animated: false)

window = UIWindow(frame: UIScreen.mainScreen().bounds)
window?.backgroundColor = UIColor.whiteColor()
window?.rootViewController = navController
window?.makeKeyAndVisible()

在MainViewController:

func goToPastSessions(sender: UIButton) {
    let pastSessionsVC = PastSessionsViewController()
    self.navigationController?.pushViewController(pastSessionsVC, animated: true)
}

func goToWriteJournalEntry(sender: UIButton) {
    let journalVC = JournalViewController(label: "Record your thoughts")
    self.navigationController?.pushViewController(journalVC, animated: true)
}

在PastSessionsViewController:

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    let editJournalVC = JournalViewController(label: "Edit your thoughts")

    let indexPath = tableView.indexPathForSelectedRow()
    let location = indexPath?.row
    let currentCell = tableView.cellForRowAtIndexPath(indexPath!) as! EntryCell

    if let objects = pastSessionsDataSource.coreDataReturn {
        if let location = location {
            editJournalVC.journalEntryCoreDataLocation = location
            editJournalVC.editEntry = true
            editJournalVC.journalEntryToEdit = objects[location].journalEntry
        }
    }

    self.navigationController?.presentViewController(editJournalVC, animated: true, completion: nil)
}

最后,在JournalViewController:

func doneJournalEntry(sender: UIButton) {
    journalEntryTextArea?.resignFirstResponder()
    var entry = journalEntryTextArea?.text

    if let entry = entry {
        let appDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
        let managedObjectContext = appDelegate.managedObjectContext!
        let request = NSFetchRequest(entityName: "Session")
        var error: NSError?

        // new entry
        if journalEntryText == "Record your thoughts" {
            let result = managedObjectContext.executeFetchRequest(request, error: &error)

            if let objects = result as? [Session] {
                if let lastTime = objects.last {
                    lastTime.journalEntry = entry
                }
            }
        } else {
            // existing entry
            let sortDescriptor = NSSortDescriptor(key: "date", ascending: false)
            request.sortDescriptors = [sortDescriptor]

            let result = managedObjectContext.executeFetchRequest(request, error: &error)
            if let objects = result as? [Session] {
                var location = journalEntryCoreDataLocation

                var object = objects[location!]
                object.journalEntry = entry
            }
        }

        if !managedObjectContext.save(&error) {
            println("save failed: \(error?.localizedDescription)")
        }
    }

   // in "edit" mode, self.navigationController is `nil` and this fails
   // in "record a new entry" mode, it's not nil and works fine
    self.navigationController?.popViewControllerAnimated(true)
}

func cancelEntryOrEditAndReturn(sender: UIButton) {
    self.journalEntryTextArea?.resignFirstResponder()

   // in "edit" mode, self.navigationController is `nil` and this fails
   // in "record a new entry" mode, it's not nil and works fine
    self.navigationController?.popViewControllerAnimated(true)
}

谢谢参观

Answer 1

如果您希望它在同一个导航堆栈中,您应该推送editJournalVC而不是呈现.因为当您呈现控制器时它不再位于相同的导航堆栈中.此外,如果你提出它,你应该解雇它而不是流行.因此,如果您想要呈现控制器,您应该使用

self.dismissViewControllerAnimated(true, completion: nil)

代替

self.navigationController?.popViewControllerAnimated(true)