新表格视图单元格显示为空白单元格

Question

我一直在开发应用程序，并遇到了一些问题，因此我尽可能简单地重新构建它以找出错误发生的位置。我的代码使用CoreData，我的第一个示例包含在导航栏中的加号按钮内添加新项目的代码。换句话说，视图或segue没有变化。这个版本的工作正如我所期望的那样。请参阅以下GIF。

但是当我创建一个添加新项目的新视图控制器时，我最终得到一个空白单元格。我在加号按钮的添加按钮后面有完全相同的代码。我只是使用show segue从tableview到普通的视图控制器。但是，如果我退出应用程序并重新启动它，它们都能正确显示。见下文。

如果你很好奇，我会将它添加为1到3之间的随机数。我的猜测是我需要做一些关于segue但我不知道它是什么。我在Swift非常新，所以我有很多东西需要学习。

提前感谢您提供给我的任何帮助。我想如果我能解决这个问题，我终于可以继续开发我的应用了。再次感谢你。下面是我的代码，它有一个segue。

表视图控制器代码（Swift）

import UIKit
import CoreData

class ListItemsTVC: UITableViewController, NSFetchedResultsControllerDelegate {

// MARK: - Constants and Variables

let moc = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
var frc: NSFetchedResultsController = NSFetchedResultsController()

// MARK: - App loading Functions

override func viewDidLoad() {
    super.viewDidLoad()

    frc = getFCR()
    frc.delegate = self

    do {
        try frc.performFetch()
    } catch {
        print("Failed to perform inital fetch")
    }
    self.tableView.rowHeight = 62

}

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

// MARK: - Outlets and Actions

/*@IBAction func addItem(sender: AnyObject) {

    let entityDesc = NSEntityDescription.entityForName("Items", inManagedObjectContext: moc)
    let item = Items(entity: entityDesc!, insertIntoManagedObjectContext: moc)

    if (NSUserDefaults.standardUserDefaults().objectForKey("nextItemID") == nil) {
        NSUserDefaults.standardUserDefaults().setObject(1, forKey: "nextItemID")
        NSUserDefaults.standardUserDefaults().synchronize()
    }

    let id = NSUserDefaults.standardUserDefaults().integerForKey("nextItemID")

    item.id = id
    switch id {
    case 1...9:
        item.name = "Item ID: 0\(id)"
    default:
        item.name = "Item ID: \(id)"
    }
    item.brand = "Brand \(id)"
    item.qty = 1
    item.price = 0
    item.size = "Size \(id)"
    let sec: Int = Int(arc4random_uniform(UInt32(4 - 1))) + 1
    item.section = "Section \(sec)"
    item.isChecked = false

    do {
        try moc.save()
        NSUserDefaults.standardUserDefaults().setObject(id + 1, forKey: "nextItemID")
        NSUserDefaults.standardUserDefaults().synchronize()
    } catch {
        fatalError("New item save failed")
    }

}*/

// MARK: - Table view data source

override func numberOfSectionsInTableView(tableView: UITableView) -> Int {

    if let sections = frc.sections {
        return sections.count
    }

    return 0

}

override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

    if let sections = frc.sections {
        let currentSection = sections[section]
        return currentSection.numberOfObjects
    }

    return 0

}

override func tableView(tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {

    return 28

}

override func tableView(tableView: UITableView, titleForHeaderInSection section: Int) -> String? {

    if let sections = frc.sections {
        let currentSection = sections[section]
        return currentSection.name
    }

    return nil

}

func controllerWillChangeContent(controller: NSFetchedResultsController) {

    tableView.beginUpdates()

}

func controllerDidChangeContent(controller: NSFetchedResultsController) {

    tableView.endUpdates()

}

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    let cell = tableView.dequeueReusableCellWithIdentifier("listContentCell", forIndexPath: indexPath) as! ListItemsTVCell
    let item = frc.objectAtIndexPath(indexPath) as! Items

    cell.separatorInset = UIEdgeInsets(top: 0, left: 78, bottom: 0, right: 0)
    cell.itemName.text = item.name
    cell.itemSection.text = item.section
    cell.itemQty.text = "Qty: \(item.qty!)"
    cell.itemSize.text = item.size
    cell.itemPrice.text = floatToCurrency(Float(item.price!))
    //cell.itemImage.image = UIImage(data: item.image!)
    cell.itemID.text = String(item.id!)

    return cell

}

override func tableView(tableView: UITableView, editActionsForRowAtIndexPath indexPath: NSIndexPath) -> [UITableViewRowAction]? {

    let delete = UITableViewRowAction(style: .Destructive, title: "Delete") { (action, indexPath) in

        let item = self.frc.objectAtIndexPath(indexPath) as! Items
        let id = item.id!
        let request = self.fetchRequest()
        let pred = NSPredicate(format: "%K == %@", "id",id)
        request.predicate = pred
        var fetchResults = [AnyObject]()

        do {
            fetchResults = try self.moc.executeFetchRequest(request)
        } catch {
            fatalError("Fetching Data to Delete Failed")
        }

        self.moc.deleteObject(fetchResults[0] as! NSManagedObject)
        fetchResults.removeAtIndex(0)

        do {
            try self.moc.save()
        } catch {
            fatalError("Failed to Save after Delete")
        }

    }

    return [delete]

}

func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType) {

    switch type {
    case NSFetchedResultsChangeType.Delete:
        self.tableView.deleteSections(NSIndexSet(index: sectionIndex), withRowAnimation: UITableViewRowAnimation.Automatic)
    case NSFetchedResultsChangeType.Insert:
        self.tableView.insertSections(NSIndexSet(index: sectionIndex), withRowAnimation: UITableViewRowAnimation.Automatic)
        /*case NSFetchedResultsChangeType.Update:
         tableView.reloadSections(NSIndexSet(index: sectionIndex), withRowAnimation: UITableViewRowAnimation.Automatic)*/
    default:
        print("Default in didChangeSection was called")
        break
    }

}

internal func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {

    switch type {
    case NSFetchedResultsChangeType.Delete:
        self.tableView.deleteRowsAtIndexPaths([indexPath!], withRowAnimation: UITableViewRowAnimation.Automatic)
    case NSFetchedResultsChangeType.Insert:
        self.tableView.insertRowsAtIndexPaths([newIndexPath!], withRowAnimation: UITableViewRowAnimation.Fade)
    default:
        print("Default in didChangeObject was called")
        break
    }

}

/*
// 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 the specified item to be editable.
    return true
}
*/

/*
// Override to support editing the table view.
override func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
    if editingStyle == .Delete {
        // Delete the row from the data source
        tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
    } else if editingStyle == .Insert {
        // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
    }    
}
*/

/*
// 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.
    return true
}
*/

/*

// MARK: - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    // Get the new view controller using segue.destinationViewController.
    // Pass the selected object to the new view controller.
}
*/

// MARK: - Custom Functions

func fetchRequest() -> NSFetchRequest {

    let fetchRequest = NSFetchRequest(entityName: "Items")
    let sortDesc1 = NSSortDescriptor(key: "section", ascending: true)
    let sortDesc2 = NSSortDescriptor(key: "isChecked", ascending: true)
    let sortDesc3 = NSSortDescriptor(key: "name", ascending: true)
    fetchRequest.sortDescriptors = [sortDesc1, sortDesc2, sortDesc3]

    return fetchRequest

}

func getFCR() -> NSFetchedResultsController {

    frc = NSFetchedResultsController(fetchRequest: fetchRequest(), managedObjectContext: moc, sectionNameKeyPath: "section" , cacheName: nil)

    return frc

}

func floatToCurrency(flt: Float) -> String {

    let formatter = NSNumberFormatter()
    formatter.numberStyle = NSNumberFormatterStyle.CurrencyStyle
    return String(formatter.stringFromNumber(flt)!)

}

}

View Controller（Swift）[segue view]

import UIKit
import CoreData

class AddItemListVC: UIViewController, NSFetchedResultsControllerDelegate {

// MARK: - Constants and Variables

let moc = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
//var frc: NSFetchedResultsController = NSFetchedResultsController()

// MARK: - App loading Functions

override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view.
}

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

// MARK: - Outlets and Actions

@IBAction func addItem(sender: AnyObject) {

    let entityDesc = NSEntityDescription.entityForName("Items", inManagedObjectContext: moc)
    let item = Items(entity: entityDesc!, insertIntoManagedObjectContext: moc)

    if (NSUserDefaults.standardUserDefaults().objectForKey("nextItemID") == nil) {
        NSUserDefaults.standardUserDefaults().setObject(1, forKey: "nextItemID")
        NSUserDefaults.standardUserDefaults().synchronize()
    }

    let id = NSUserDefaults.standardUserDefaults().integerForKey("nextItemID")

    item.id = id
    switch id {
    case 1...9:
        item.name = "Item ID: 0\(id)"
    default:
        item.name = "Item ID: \(id)"
    }
    item.brand = "Brand \(id)"
    item.qty = 1
    item.price = 0
    item.size = "Size \(id)"
    let sec: Int = Int(arc4random_uniform(UInt32(4 - 1))) + 1
    item.section = "Section \(sec)"
    item.isChecked = false

    do {
        try moc.save()
        NSUserDefaults.standardUserDefaults().setObject(id + 1, forKey: "nextItemID")
        NSUserDefaults.standardUserDefaults().synchronize()
    } catch {
        fatalError("New item save failed")
    }

}

/*
// MARK: - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    // Get the new view controller using segue.destinationViewController.
    // Pass the selected object to the new view controller.
}
*/

}

Answer 1

将TableView数据重新加载为android:focusable="false"方法为：

viewWillAppear

当您从override func viewWillAppear() { super.viewWillAppear() do { try frc.performFetch() } catch { print("Failed to perform inital fetch") } } 导航回来时，您并没有告诉viewController更新tableView，所以请在viewWillAppear中执行，因为当您弹出navController返回时它会触发。

Answer 2

以下是为我解决问题的代码。我只更改了表视图控制器代码：

import UIKit
import CoreData

class ListItemsTVC: UITableViewController, NSFetchedResultsControllerDelegate {

// MARK: - Constants and Variables

let moc = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
var frc: NSFetchedResultsController = NSFetchedResultsController()

// MARK: - App loading Functions

override func viewDidLoad() {
    super.viewDidLoad()

    frc = getFCR()
    frc.delegate = self

    do {
        try frc.performFetch()
    } catch {
        print("Failed to perform inital fetch")
    }
    self.tableView.rowHeight = 62

}

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)

    self.tableView.reloadData()

}

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

// MARK: - Outlets and Actions

/*@IBAction func addItem(sender: AnyObject) {

    let entityDesc = NSEntityDescription.entityForName("Items", inManagedObjectContext: moc)
    let item = Items(entity: entityDesc!, insertIntoManagedObjectContext: moc)

    if (NSUserDefaults.standardUserDefaults().objectForKey("nextItemID") == nil) {
        NSUserDefaults.standardUserDefaults().setObject(1, forKey: "nextItemID")
        NSUserDefaults.standardUserDefaults().synchronize()
    }

    let id = NSUserDefaults.standardUserDefaults().integerForKey("nextItemID")

    item.id = id
    switch id {
    case 1...9:
        item.name = "Item ID: 0\(id)"
    default:
        item.name = "Item ID: \(id)"
    }
    item.brand = "Brand \(id)"
    item.qty = 1
    item.price = 0
    item.size = "Size \(id)"
    let sec: Int = Int(arc4random_uniform(UInt32(4 - 1))) + 1
    item.section = "Section \(sec)"
    item.isChecked = false

    do {
        try moc.save()
        NSUserDefaults.standardUserDefaults().setObject(id + 1, forKey: "nextItemID")
        NSUserDefaults.standardUserDefaults().synchronize()
    } catch {
        fatalError("New item save failed")
    }

}*/

// MARK: - Table view data source

override func numberOfSectionsInTableView(tableView: UITableView) -> Int {

    if let sections = frc.sections {
        return sections.count
    }

    return 0

}

override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

    if let sections = frc.sections {
        let currentSection = sections[section]
        return currentSection.numberOfObjects
    }

    return 0

}

override func tableView(tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {

    return 28

}

override func tableView(tableView: UITableView, titleForHeaderInSection section: Int) -> String? {

    if let sections = frc.sections {
        let currentSection = sections[section]
        return currentSection.name
    }

    return nil

}

func controllerWillChangeContent(controller: NSFetchedResultsController) {

    tableView.beginUpdates()

}

func controllerDidChangeContent(controller: NSFetchedResultsController) {

    tableView.endUpdates()

}

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    let cell = tableView.dequeueReusableCellWithIdentifier("listContentCell", forIndexPath: indexPath) as! ListItemsTVCell
    let item = frc.objectAtIndexPath(indexPath) as! Items

    cell.separatorInset = UIEdgeInsets(top: 0, left: 78, bottom: 0, right: 0)
    cell.itemName.text = item.name
    cell.itemSection.text = item.section
    cell.itemQty.text = "Qty: \(item.qty!)"
    cell.itemSize.text = item.size
    cell.itemPrice.text = floatToCurrency(Float(item.price!))
    //cell.itemImage.image = UIImage(data: item.image!)
    cell.itemID.text = String(item.id!)

    return cell

}

override func tableView(tableView: UITableView, editActionsForRowAtIndexPath indexPath: NSIndexPath) -> [UITableViewRowAction]? {

    let delete = UITableViewRowAction(style: .Destructive, title: "Delete") { (action, indexPath) in

        let item = self.frc.objectAtIndexPath(indexPath) as! Items
        let id = item.id!
        let request = self.fetchRequest()
        let pred = NSPredicate(format: "%K == %@", "id",id)
        request.predicate = pred
        var fetchResults = [AnyObject]()

        do {
            fetchResults = try self.moc.executeFetchRequest(request)
        } catch {
            fatalError("Fetching Data to Delete Failed")
        }

        self.moc.deleteObject(fetchResults[0] as! NSManagedObject)
        fetchResults.removeAtIndex(0)

        do {
            try self.moc.save()
        } catch {
            fatalError("Failed to Save after Delete")
        }

    }

    return [delete]

}

func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType) {

    switch type {
    case NSFetchedResultsChangeType.Delete:
        self.tableView.deleteSections(NSIndexSet(index: sectionIndex), withRowAnimation: UITableViewRowAnimation.Automatic)
    case NSFetchedResultsChangeType.Insert:
        self.tableView.insertSections(NSIndexSet(index: sectionIndex), withRowAnimation: UITableViewRowAnimation.Automatic)
        /*case NSFetchedResultsChangeType.Update:
         tableView.reloadSections(NSIndexSet(index: sectionIndex), withRowAnimation: UITableViewRowAnimation.Automatic)*/
    default:
        print("Default in didChangeSection was called")
        break
    }

}

internal func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {

    switch type {
    case NSFetchedResultsChangeType.Delete:
        self.tableView.deleteRowsAtIndexPaths([indexPath!], withRowAnimation: UITableViewRowAnimation.Automatic)
    case NSFetchedResultsChangeType.Insert:
        self.tableView.insertRowsAtIndexPaths([newIndexPath!], withRowAnimation: UITableViewRowAnimation.Fade)
    default:
        print("Default in didChangeObject was called")
        break
    }

}

/*
// 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 the specified item to be editable.
    return true
}
*/

/*
// Override to support editing the table view.
override func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
    if editingStyle == .Delete {
        // Delete the row from the data source
        tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
    } else if editingStyle == .Insert {
        // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
    }    
}
*/

/*
// 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.
    return true
}
*/

/*

// MARK: - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    // Get the new view controller using segue.destinationViewController.
    // Pass the selected object to the new view controller.
}
*/

// MARK: - Custom Functions

func fetchRequest() -> NSFetchRequest {

    let fetchRequest = NSFetchRequest(entityName: "Items")
    let sortDesc1 = NSSortDescriptor(key: "section", ascending: true)
    let sortDesc2 = NSSortDescriptor(key: "isChecked", ascending: true)
    let sortDesc3 = NSSortDescriptor(key: "name", ascending: true)
    fetchRequest.sortDescriptors = [sortDesc1, sortDesc2, sortDesc3]

    return fetchRequest

}

func getFCR() -> NSFetchedResultsController {

    frc = NSFetchedResultsController(fetchRequest: fetchRequest(), managedObjectContext: moc, sectionNameKeyPath: "section" , cacheName: nil)

    return frc

}

func floatToCurrency(flt: Float) -> String {

    let formatter = NSNumberFormatter()
    formatter.numberStyle = NSNumberFormatterStyle.CurrencyStyle
    return String(formatter.stringFromNumber(flt)!)

}

}

Answer 3

穆罕默德的答案肯定会解决问题，因为每次viewWillAppear调用时它都会触发表视图的重新加载。但问题是这不是一个很好的方法。

你看，Starting a new Gradle Daemon for this build (subsequent builds will be faster). 被召唤了很多次。它是一个UIViewController生命周期方法。如果您要转到第二个视图控制器并在没有按下添加按钮的情况下返回，它仍将重新加载UITableView。现在，重点不在于它是否是一项昂贵的操作，重点是viewWillAppear不是那种做某种东西的地方。如果在重新加载单元格之前必须执行其他操作，那么您可能不希望将其全部放在那里并冒着创建错误的风险。

实现这一目标的一个好方法是通过代表（回拨）。阅读更多相关内容，您将看到它为您提供了急需的灵活性。