问题
I've been working on an app, and ran into some problems, so I rebuilt it as simple as possible to find where the error happens at. My code uses CoreData, and my first example has the code for adding new items inside the plus button in the navigation bar. In other words, there is no change of view or segue. This version works as I would expect it to. See the following GIF.
But when I make a new view controller that adds the new item, I end up getting a blank cell instead. I have the exact same code behind the add button that I had in the plus button. And I just use a show segue to get from the tableview to a normal view controller. But if I quit the app and start it back up, it all shows correctly. See below.
If you are curious, I have the section it is adding to being a random number between 1 and 3. My guess is there is something I need to do with that segue but I don't have clue what it is. I'm very new at Swift so I have lots to learn.
Thank you in advance for any help you can give me. I think if I can solve this problem, I can finally move forward with developing my app. Thank you again. Below is my code for the case where it has a segue.
Table View Controller Code (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) [The 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.
}
*/
}
回答1:
Reload TableView Data is viewWillAppear method as :
override func viewWillAppear() {
super.viewWillAppear()
do {
try frc.performFetch()
} catch {
print("Failed to perform inital fetch")
}
}
As when you are navigating back from viewController you are not telling the TableViewController to update tableView so do it in viewWillAppear as it will fire when you are popping navController to come back.
回答2:
Here is the code that fixed the problem for me. I only changed the Table View Controller Code:
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)!)
}
}
回答3:
Muhammad's answer will surely solve the problem as it will trigger the reload of the table view every time viewWillAppear will call. But the problem is that is not a very good way of doing this.
You see, viewWillAppear gets called a lot of times. It is a UIViewController life cycle method. If you are going to the second view controller and coming back without pressing the add button, it will still reload the UITableView. Now, the point is not whether it is an expensive operation or not, the point is that viewWillAppear is not the place to do that kind of a stuff. What if you had to do something else before reloading the cell, you may not want to put it all there and risk creating bugs.
A good way of achieving this is through delegates (call backs). Read up more on this and you will see that it gives you a much needed flexibility.
来源：https://stackoverflow.com/questions/36994649/new-table-view-cell-shows-as-a-blank-cell