How to update footer in Section via DiffableDataSource without causing flickering effect? - ios

A Section may contain 1 header, many content items and 1 footer.
For DiffableDataSource, most of the online examples, are using enum to represent Section. For instance
func applySnapshot(_ animatingDifferences: Bool) {
var snapshot = Snapshot()
snapshot.appendSections([.MainAsEnum])
snapshot.appendItems(filteredTabInfos, toSection: .MainAsEnum)
dataSource?.apply(snapshot, animatingDifferences: animatingDifferences)
}
However, when the Section has a dynamic content footer, we may need to use struct to represent Section. For instance
import Foundation
struct TabInfoSection {
// Do not include content items [TabInfo] as member of Section. If not, any mutable
// operation performed on content items, will misguide Diff framework to throw
// away entire current Section, and replace it with new Section. This causes
// flickering effect.
var footer: String
}
extension TabInfoSection: Hashable {
}
But, how are we suppose to update only footer?
The current approach provided by
DiffableDataSource: Snapshot Doesn't reload Headers & footers is not entirely accurate
If I try to update footer
class TabInfoSettingsController: UIViewController {
…
func applySnapshot(_ animatingDifferences: Bool) {
var snapshot = Snapshot()
let section = tabInfoSection;
snapshot.appendSections([section])
snapshot.appendItems(filteredTabInfos, toSection: section)
dataSource?.apply(snapshot, animatingDifferences: animatingDifferences)
}
var footerValue = 100
extension TabInfoSettingsController: TabInfoSettingsItemCellDelegate {
func crossButtonClick(_ sender: UIButton) {
let hitPoint = (sender as AnyObject).convert(CGPoint.zero, to: collectionView)
if let indexPath = collectionView.indexPathForItem(at: hitPoint) {
// use indexPath to get needed data
footerValue = footerValue + 1
tabInfoSection.footer = String(footerValue)
//
// Perform UI updating.
//
applySnapshot(true)
}
}
}
I will get the following flickering outcome.
The reason of flickering is that, the diff framework is throwing entire old Section, and replace it with new Section, as it discover there is change in TabInfoSection object.
Is there a good way, to update footer in Section via DiffableDataSource without causing flickering effect?
p/s The entire project source code can be found in https://github.com/yccheok/ios-tutorial/tree/broken-demo-for-footer-updating under folder TabDemo.

Have you thought about making a section only for the footer? So that way there's no reload, when it flickers, since it's technically not apart of the problematic section?

There is a fast fix for it, but you will loose the animation of the tableview. In TabInfoSettingsController.swift you can force false the animations in this function:
func applySnapshot(_ animatingDifferences: Bool) {
var snapshot = Snapshot()
let section = tabInfoSection;
snapshot.appendSections([section])
snapshot.appendItems(filteredTabInfos, toSection: section)
dataSource?.apply(snapshot, animatingDifferences: false)
}
You will not see the flickering effect but you will loose the standard animation.

if you want to update only collectionview footer text then make it variable of TabInfoSettingsFooterCell.
var tableSection: TabInfoSettingsFooterCell?
DataSource
func makeDataSource() -> DataSource {
let dataSource = DataSource(
collectionView: collectionView,
cellProvider: { (collectionView, indexPath, tabInfo) -> UICollectionViewCell? in
guard let tabInfoSettingsItemCell = collectionView.dequeueReusableCell(
withReuseIdentifier: TabInfoSettingsController.tabInfoSettingsItemCellClassName,
for: indexPath) as? TabInfoSettingsItemCell else {
return nil
}
tabInfoSettingsItemCell.delegate = self
tabInfoSettingsItemCell.reorderDelegate = self
tabInfoSettingsItemCell.textField.text = tabInfo.getPageTitle()
return tabInfoSettingsItemCell
}
)
dataSource.supplementaryViewProvider = { collectionView, kind, indexPath in
guard kind == UICollectionView.elementKindSectionFooter else {
return nil
}
let section = dataSource.snapshot().sectionIdentifiers[indexPath.section]
guard let tabInfoSettingsFooterCell = collectionView.dequeueReusableSupplementaryView(
ofKind: kind,
withReuseIdentifier: TabInfoSettingsController.tabInfoSettingsFooterCellClassName,
for: indexPath) as? TabInfoSettingsFooterCell else {
return nil
}
tabInfoSettingsFooterCell.label.text = section.footer
//set tableSection value
self.tableSection = tabInfoSettingsFooterCell
return tabInfoSettingsFooterCell
}
return dataSource
}
TabInfoSettingsItemCellDelegate
func crossButtonClick(_ sender: UIButton) {
let hitPoint = (sender as AnyObject).convert(CGPoint.zero, to: collectionView)
if let indexPath = collectionView.indexPathForItem(at: hitPoint) {
footerValue = footerValue + 1
tabInfoSection.footer = String(footerValue)
//Update section value
self.tableSection?.label.text = String(footerValue)
}
}

Related

Ios images and labels keep loading while scrolling

I'm writing a demo to show user's tweets.
The question is:
Every time I scroll to the bottom and then scroll back, the tweet's images and comments are reloaded, even the style became mess up. I know it something do with dequeue, I set Images(which is an array of UIImageView) to [] every time after dequeue, but it is not working. I'm confused and couldn't quite sleep....
Here is core code of my TableCell(property and Images set), which provide layout:
class WechatMomentListCell: UITableViewCell{
static let identifier = "WechatMomentListCell"
var content = UILabel()
var senderAvatar = UIImageView()
var senderNick = UILabel()
var images = [UIImageView()]
var comments = [UILabel()]
override func layoutSubviews() {
//there is part of Image set and comments
if images.count != 0 {
switch images.count{
case 1:
contentView.addSubview(images[0])
images[0].snp.makeConstraints{ (make) in
make.leading.equalTo(senderNick.snp.leading)
make.top.equalTo(content.snp.bottom)
make.width.equalTo(180)
make.height.equalTo(180)
}
default:
for index in 0...images.count-1 {
contentView.addSubview(images[index])
images[index].snp.makeConstraints{ (make) in
make.leading.equalTo(senderNick.snp.leading).inset(((index-1)%3)*109)
make.top.equalTo(content.snp.bottom).offset(((index-1)/3)*109)
make.width.equalTo(90)
make.height.equalTo(90)
}
}
}
}
if comments.count != 0, comments.count != 1 {
for index in 1...comments.count-1 {
comments[index].backgroundColor = UIColor.gray
contentView.addSubview(comments[index])
comments[index].snp.makeConstraints{(make) in
make.leading.equalTo(senderNick)
make.bottom.equalToSuperview().inset(index*20)
make.width.equalTo(318)
make.height.equalTo(20)
}
}
}
}
Here is my ViewController, which provide datasource:
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
guard let tweetCell = tableView.dequeueReusableCell(withIdentifier: WechatMomentListCell.identifier, for: indexPath) as? WechatMomentListCell else {
fatalError("there is no WechatMomentList")
}
let tweet = viewModel.tweetList?[indexPath.row]
for i in tweet?.images ?? [] {
let flagImage = UIImageView()
flagImage.sd_setImage(with: URL(string: i.url))
tweetCell.images.append(flagImage)
}
for i in tweet?.comments ?? [] {
let flagComment = UILabel()
flagComment.text = "\(i.sender.nick) : \(i.content)"
tweetCell.comments.append(flagComment)
}
return tweetCell
}
The Images GET request has been define at ViewModel using Alamofire.
The firsttime is correct. However, If I scroll the screen, the comments will load again and images were mess up like this.
I found the problem in your tableview cell. in cell you have two variables like this.
var images = [UIImageView()]
var comments = [UILabel()]
Every time you using this cell images and comments are getting appended. make sure you reset these arrays every time you use this cell. like setting theme empty at initialization.

Swift Diffable datasource will crash when Firebase .observe() updates values

I am building an app where a user can read articles. Each article is written by an author, so, on the article view, when the user clicks on the author's profile picture it navigates to the Author's profile view.
In the Author Profile view, there is a "Follow" button, and in the same view, there are the statistics of the Author (ex. how many articles he/she wrote, how many followers they have, etc.). Something very close to this:
When the author profile view loads, everything is OK. But as soon as the user touches the "Follow" button, the app crashes with the following error:
Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Section identifier count does not match data source count. This is most likely due to a hashing issue with the identifiers.'
These are the steps I follow:
User in the Author Profile view
User sees the "Follow" button and the stats showing how many users are following the author
Say the author has 10 followers. The user touches the "Follow" button
Behind the scenes, I go into Firebase, get the author, and add the userID into an array of strings: followers: ["asdm132123", "asdadsa12931", "!123123jsdfjsf"] by using .observeSingleEvent() and setValue()
Then I read the data using the .observe() method of Firebase, to update the button state from "Follow" --> "Following" and increase the followers' value from "10" --> "11"
Edit: Code part:
enum AuthorProfileSection {
case details
case stats
case articles
}
Datasource creation:
func configureDataSource() -> UICollectionViewDiffableDataSource<AuthorProfileSection, AnyHashable> {
let dataSource = UICollectionViewDiffableDataSource<AuthorProfileSection, AnyHashable>(collectionView: collectionView) { (collectionView, indexPath, object) -> UICollectionViewCell? in
if let object = object as? Author {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: AuthorDetailsCell.reuseIdentifier, for: indexPath) as! AuthorDetailsCell
cell.configure(with: object)
return cell
}
if let object = object as? AuthorStatsForAuthorProfile {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: AuthorStatCell.reuseIdentifier, for: indexPath) as! AuthorStatCell
cell.configure(with: object)
return cell
}
if let object = object as? Article {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: AuthorArticleCell.reuseIdentifier, for: indexPath) as! AuthorArticleCell
cell.configure(with: object)
return cell
}
return nil
}
return dataSource
}
Updating snapshot
fileprivate func updateSnapshot(animated: Bool = false) {
guard let authorUID = authorUID else { return }
Firebase.Database.database().fetchSelectedAuthorProfileData( authorUID: authorUID, fromArticleUID: self.articleUID) { authorProfileSection in
var snapshot = self.dataSource.snapshot()
// sections
snapshot.appendSections([.details, .stats, .articles])
snapshot.appendItems([authorProfileSection.details], toSection: .details)
snapshot.appendItems(authorProfileSection.stats ?? [], toSection: .stats)
snapshot.appendItems(authorProfileSection.articles ?? [], toSection: .articles)
self.dataSource.apply(snapshot, animatingDifferences: animated)
}
}
And the cell:
class AuthorStatCell: UICollectionViewCell, SelfConfiguringCell {
typealias someType = AuthorStatsForAuthorProfile
static var reuseIdentifier = "AuthorStatCell"
override init(frame: CGRect) {
super.init(frame: frame)
buildUI()
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func configure(with data: AuthorStatsForAuthorProfile) {
print(data)
}
fileprivate func buildUI() {
backgroundColor = UIColor(red: 0.20, green: 0.83, blue: 0.60, alpha: 1.00)
layer.cornerRadius = 15
}
}
And this is the result (in red the part that changes if I touch the "follow" button):
Here is where the app crashes. Any idea why?
I suspect, the issue is inside updateSnapshot() you are getting the current snapshot and adding 3 new sections to it every time you touch follow button
var snapshot = self.dataSource.snapshot()
// sections
snapshot.appendSections([.details, .stats, .articles])
try this
var snapshot = NSDiffableDataSourceSnapshot<AuthorProfileSection, AnyHashable>()
Or if you are calling another func like createSnapshot Before updateSnapshot then just try removing the line of appendSections
var snapshot = self.dataSource.snapshot()
// sections
// remove it
//snapshot.appendSections([.details, .stats, .articles])
snapshot.appendItems([authorProfileSection.details], toSection: .details)
snapshot.appendItems(authorProfileSection.stats ?? [], toSection: .stats)
snapshot.appendItems(authorProfileSection.articles ?? [], toSection: .articles)
self.dataSource.apply(snapshot, animatingDifferences: animated)
I’m not sure 100% 🤔 about it bcs I just on my phone rn

Pull to refresh in a tableview rx datasource

In my mobile application I would like to update the tableView datasource by a pull to refresh request, but I don't know how to insert the new items on top of the tableview datasource.
I see that there is a a method of insertRows such as : self.tableView?.insertRows(at: [indexPath], with: .top) but how do I add the newItems here according to my methods I have?
I have a function called initializedTableView() that initializes the tableView with PublishSubject observable items.
func initializeTableView() {
viewModel
.items
.subscribe(onNext: { items in
self.tableView?.delegate = nil
self.tableView?.dataSource = nil
Observable.just(items)
.bind(to:(self.tableView?.rx.items(cellIdentifier:
itemCell.Identifier, cellType: itemCell.self))!) {
(index, element, cell) in
cell.itemModel = element
}.disposed(by: self.disposeBag)
})
.disposed(by: disposeBag)
}
This function is called once a pull to refresh is requested by user:
func refreshTableView() {
// get new items
viewModel
.newItems
.subscribe(onNext: { newItems in
//new
let new = newItems.filter({ item in
// items.new == true
})
//old
var old = newItems.filter({ item -> Bool in
// items.new == false
})
new.forEach({item in
// how to update tableView.rx.datasource here???
})
}).disposed(by: disposeBag)
}
struct ViewModel {
let items: BehaviorRelay<[Item]>
init() {
self.items = BehaviorRelay(value: [])
}
func fetchNewItems() {
// This assumes you are properly distinguishing which items are new
// and `newItems` does not contain existing items
let newItems: [Item] = /* However you get new items */
// Get a copy of the current items
var updatedItems = self.items.value
// Insert new items at the beginning of currentItems
updatedItems.insert(contentsOf: newItems, at: 0)
// For simplicity this answer assumes you are using a single cell and are okay with a reload
// rather than the insert animations.
// This will reload your tableView since 'items' is bound to the tableView items
//
// Alternatively, you could use RxDataSources and use the `RxTableViewSectionedAnimatedDataSource`
// This will require a section model that conforms to `AnimatableSectionModelType` and some
// overall reworking of this example
items.accept(updatedItems)
}
}
final class CustomViewController: UIViewController {
deinit {
disposeBag = DisposeBag()
}
#IBOutlet weak var tableView: UITableView!
private var disposeBag = DisposeBag()
private let viewModel = ViewModel()
override func viewDidLoad() {
super.viewDidLoad()
tableView.register(CustomTableCell.self, forCellReuseIdentifier: "ReuseID")
tableView.refreshControl = UIRefreshControl()
viewModel.items
.bind(to: tableView.rx.items(cellIdentifier: "ReuseID", cellType: CustomTableCell.self)) { row, item, cell in
// Configure cell with item
cell.configure(with: item)
}
.disposed(by: disposeBag)
tableView.refreshControl?.rx.controlEvent(.valueChanged)
.subscribe(onNext: { [weak self] in
self?.viewModel.fetchNewItems()
})
.disposed(by: disposeBag)
}
}
Alternative answer using BehaviorRelay and bindings. This way, you are only updating the items relay and it will automatically update the tableView. It also provides a more "Rx" way of handling pull to refresh.
As mentioned in the code comments, this assumes you are determining which items are new and that newItems does not contain any existing items. Either way this should provide a starting point.
struct ViewModel {
let items: Observable<[Item]>
init(trigger: Observable<Void>, newItems: #escaping () -> Observable<[Item]>) {
items = trigger
.flatMapLatest(newItems)
.scan([], accumulator: { $1 + $0 })
}
}
The above doesn't handle errors, nor does it handle resets, but the scan will put the new items at the top of the list.
The situation doesn't feel right though. Normally, the API call returns all the items, how can it possibly know which items are "new"?
I did something similar with my app since I had issues with tableView.insertRows.
Here is the code:
func loadMoreComments() {
// call to backend to get more comments
getMoreComments { (newComments) in
// combine the new data and your existing data source array
self.comments = newComments + self.comments
self.tableView.reloadData()
self.tableView.layoutIfNeeded()
// calculate the total height of the newly added cells
var addedHeight: CGFloat = 0
for i in 0...result.count {
let indexRow = i
let tempIndexPath = IndexPath(row: Int(indexRow), section: 0)
addedHeight = addedHeight + self.tableView.rectForRow(at: tempIndexPath).height
}
// adjust the content offset by how much height was added to the start so that it looks the same to the user
self.tableView.contentOffset.y = self.tableView.contentOffset.y + addedHeight
}
}
So, by calculating the heights of the new cells being added to the start and then adding this calculated height to the tableView.contentOffset.y, I was able to add cells to the top of the tableView seamlessly without reworking my tableView. This may look like a jerky workaround, but the shift in tableView.contentOffset isn't noticeable if you calculate the height properly.

UITableViewController's Cell's Content disappearing

I am making a coin collection app which is supposed to help users maintain a portable record of their collection. There are two view controllers so far: the CoinTableViewController which presents a tableview of all the categories of coins, and the CoinCategoryViewController which is supposed to have a table view of the specific coins in this category.
I obviously want my coins to be reportable based on multiple criteria (such as the same year, same country, etc. and etc.). To this effect, I have created a reusable tableview cell subclass called CoinTableViewCell that has 5 UILabels which represent all the information that the coins into the collection can be grouped into categories by.
Here is what my storyboard looks like
The logic is that based on my current sorting criteria, I can hide certain labels from the cell to reflect the criteria that the coins were sorted by. The settings wheel opens up a menu that appears on the left side of the screen with options for how to sort the coins, and the closing of the menu makes the Coin Categories controller resort the coins in the collection if the sorting option was changed.
My problem is that while my program works overall, sometimes, some of the cells do not appear completely after the program resorts them (after the user opens up the menu and selects an option).
Here's what this looks like:
As you may see, the bottom two cells in the view controller are missing the top label even though the other cells have them. And since I have implemented the tableview controller's cells as being resizable, the table view cells should automatically resize themselves to fit the content inside.
Here is my code:
// Controls the table view controller showing the general coins (one per each category)
import UIKit
import CoreData
class CoinTableViewController: UITableViewController, NSFetchedResultsControllerDelegate, UISearchResultsUpdating, UITabBarControllerDelegate
{
//this is an array of all the coins in the collection
//each row of this two-dimensional array represents a new category
var coinsByCategory: [CoinCategoryMO] = []
var fetchResultController: NSFetchedResultsController<CoinCategoryMO>!
//we sort the coins by the category and then display them in the view controller
//example includes [ [Iraq Dinar 1943, Iraq Dinar 1200], etc. etc.]
//<OTHER VARIABLES HERE>
//the data here is used for resorting the coins into their respective categories
//the default sorting criteria is sorting the coins into categories with the same country, value, and currency
//and the user can change the app's sorting criteria by opening the ConfiguringPopoverViewController and changing the sorting criteria there
private var isCurrentlyResortingCoinsIntoNewCategories : Bool = false
override func viewDidLoad()
{
super.viewDidLoad()
self.tabBarController?.delegate = self
//we now fetch the data
let fetchRequest : NSFetchRequest<CoinCategoryMO> = CoinCategoryMO.fetchRequest()
if let appDelegate = (UIApplication.shared.delegate as? AppDelegate)
{
let context = appDelegate.persistentContainer.viewContext
let sortDescriptor = NSSortDescriptor(key: "index", ascending: true)
fetchRequest.sortDescriptors = [sortDescriptor]
fetchResultController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
fetchResultController.delegate = self
do
{
try fetchResultController.performFetch()
if let fetchedObjects = fetchResultController.fetchedObjects
{
self.coinsByCategory = fetchedObjects
}
}
catch
{
print(error)
}
}
//if there is an empty area in the table view, instead of showing
//empty cells, we show a blank area
self.tableView.tableFooterView = UIView()
//we configure the row heights for the table view so that the cells are resizable.
//ALSO: should the user want to adjust the text size in "General"->"Accessibility"
//the text size in the app will be automatically adjusted for him...
tableView.estimatedRowHeight = 120
tableView.rowHeight = UITableViewAutomaticDimension
//WE CONFIGURE THE SEARCH BAR AND NAVIGATION BAR....
//if the user scrolls up, he sees a white background, not a grey one
tableView.backgroundView = UIView()
}
override func numberOfSections(in tableView: UITableView) -> Int {
return fetchResultController.sections!.count
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int
{
if searchController != nil && searchController.isActive
{
return searchResults.count
}
else
{
if let sections = fetchResultController?.sections
{
return sections[section].numberOfObjects
}
else
{
return 0
}
}
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
//configure the cell
let cellIdentifier = "Cell"
let cell = tableView.dequeueReusableCell(withIdentifier: cellIdentifier, for: indexPath) as! CoinTableViewCell
//Initialize the Cell
let category = (searchController != nil && searchController.isActive) ? searchResults[indexPath.row] : coinsByCategory[indexPath.row]
//we now remove the extra labels that we do not need
cell.configureLabelsForCategoryType(theType: (category.coinCategory?.currentCategoryType)!)
let sampleCoin : Coin = category.coinCategory!.getCoin(at: 0)!
cell.countryLabel.text = "Country: \(sampleCoin.getCountry())"
cell.valueAndDenominationLabel.text = "Value & Denom.: \(sampleCoin.valueAndDenomination)"
//now we add in the quantity
cell.quantityLabel.text = "Quantity: \(String(describing: coinsByCategory[indexPath.row].coinCategory!.count))"
//we now add in the denomination
cell.denominationOnlyLabel.text = "Denom.: \(sampleCoin.getDenomination())"
//we now add in the year
if sampleCoin.getYear() == nil
{
cell.yearLabel.text = "Year: " + (Coin.DEFAULT_YEAR as String)
}
else
{
let yearABS = abs(Int32(sampleCoin.getYear()!))
cell.yearLabel.text = "Year: \(yearABS) \(sampleCoin.getYear()!.intValue > 0 ? TimePeriods.CE.rawValue : TimePeriods.BCE.rawValue)"
}
//we add in an accessory to indicate that clicking this cell will result in more information
cell.accessoryType = .disclosureIndicator
return cell
}
func deleteCoinCategory(rowPath: IndexPath)
{
if 0 <= rowPath.row && rowPath.row < self.coinsByCategory.count
{
//we have just tested that the rowPath index is valid
if let appDelegate = (UIApplication.shared.delegate as? AppDelegate)
{
let context = appDelegate.persistentContainer.viewContext
let coinCategoryToDelete = self.fetchResultController.object(at: rowPath)
context.delete(coinCategoryToDelete)
appDelegate.saveContext()
//ok we now deleted the category, now we update the indices
updateIndices()
appDelegate.saveContext()
}
}
}
func deleteCoin(c: Coin, indexOfSelectedCategory: IndexPath) -> Bool
{
//we have a coin that we want to delete from this viewcontroller
//and the data contained in it.
//
//the parameter indexOfSelectedCategory refers to the IndexPath of the
//row in the TableView contained in THIS viewcontroller whose category
//of coins we are modifying in this method
//
//Return value: a boolean that indicates whether a single coin has
//been deleted - meaning that the user should return to the parentviewcontroller
if 0 < indexOfSelectedCategory.row && indexOfSelectedCategory.row < self.coinsByCategory.count && self.coinsByCategory[indexOfSelectedCategory.row].coinCategory?.hasCoin(c: c) == true
{
//the index is valid as it refers to a category in the coinsByCategory array
//and the examined category has the coin in question
if self.coinsByCategory[indexOfSelectedCategory.row].coinCategory?.count == 1
{
//the coin "c" that we are going to delete is the only coin in the entire category
//we reduce the problem to a simpler one that has been already solved (thanks mathematicians!)
self.deleteCoinCategory(rowPath: indexOfSelectedCategory)
return true
}
else
{
//there is more than one coin in the category
self.coinsByCategory[indexOfSelectedCategory.row].coinCategory?.removeCoin(c: c)
//we save the changes in the database...
if let appDelegate = (UIApplication.shared.delegate as? AppDelegate)
{
appDelegate.saveContext()
}
return false
}
}
return false
}
func addCoin(coinToAdd: Coin)
{
//we check over each category to see if the coin can be added
var addedToExistingCategory: Bool = false
if let appDelegate = UIApplication.shared.delegate as? AppDelegate
{
for i in 0..<self.coinsByCategory.count
{
if self.coinsByCategory[i].coinCategory?.coinFitsCategory(aCoin: coinToAdd) == true
{
//we can add the coin to the category
self.coinsByCategory[i].coinCategory = CoinCategory(coins: self.coinsByCategory[i].coinCategory!.coinsInCategory+[coinToAdd], categoryType: coinsByCategory[i].coinCategory!.currentCategoryType)
addedToExistingCategory = true
break
}
}
if addedToExistingCategory == false
{
//since the coinToAdd does not fall in the existing categories, we create a new one
let newCategory = CoinCategoryMO(context: appDelegate.persistentContainer.viewContext)
newCategory.coinCategory = CoinCategory(coins: [coinToAdd], categoryType: CoinCategory.CategoryTypes.getTheCategoryFromString(str: UserDefaults.standard.object(forKey: "currentSortingCriteria") as! NSString).rawValue)
//this index indicates that we are going to insert this newCategory into index "0" of all the categories in the table
newCategory.index = 0
}
appDelegate.saveContext()
//now since we have added the coin, we now updated the indices of each CoinCategoryMO object
updateIndices()
}
}
func coinFitsExistingCategory(coin: Coin) -> Bool
{
//this function checks if the coin can be added to the existing categories
for i in 0..<self.coinsByCategory.count
{
if self.coinsByCategory[i].coinCategory?.coinFitsCategory(aCoin: coin) == true
{
//we can add the coin to the category
return true
}
}
return false
}
func resortCoinsInNewCategories(newCategorySetting : CoinCategory.CategoryTypes?)
{
//we want to resort all the coins in the category by new sorting criteria
if newCategorySetting != nil && newCategorySetting! != CoinCategory.CategoryTypes.getTheCategoryFromString(str: UserDefaults.standard.object(forKey: "currentSortingCriteria") as! NSString)
{
//We have a valid CoinCategory.CategoryTypes sorting criteria that is different from the one currently used.
//We resort the coins in the collection by the new category
UserDefaults.standard.setValue(newCategorySetting!.rawValue, forKey: "currentSortingCriteria")
if self.coinsByCategory.count != 0
{
//we actually have some coins to resort... let's get to work!
self.isCurrentlyResortingCoinsIntoNewCategories = true
//we first get an array of all the coins in existing categories
var allCoinsArray : [Coin] = []
for i in 0..<self.coinsByCategory.count
{
allCoinsArray += self.coinsByCategory[i].coinCategory!.coinsInCategory
}
//now we need to delete all the categories in existence...
let firstCategoryIndexPath = IndexPath(row: 0, section: 0)
let numberOfCategoriesToDelete = self.coinsByCategory.count
for _ in 0..<numberOfCategoriesToDelete
{
self.deleteCoinCategory(rowPath: firstCategoryIndexPath)
}
//OK... now that we have deleted all old categories... it is time to start to create new ones...
for i in 0..<allCoinsArray.count
{
//AND we add the coin to the array!
//this function also automatically updates the indices, so it is not an issue there
self.addCoin(coinToAdd: allCoinsArray[i])
}
//we are done resorting
self.isCurrentlyResortingCoinsIntoNewCategories = false
}
}
}
private func updateIndices()
{
//this function updates the "index" property so that
//each CoinCategoryMO object in the coinsByCategory array
//has an index corresponding to its position.
//After this function is called, we must save the core data in the AppDelegate.
//
//This function is called ONLY after the changes to the CoinCategoryMO objects
//are saved in core data and the self.coinsByCategory array is updated to have
//the latest version of the data
for i in 0..<self.coinsByCategory.count
{
//the only reason why we create an entirely new CoinCategory object
//is that the creation of an entirely new CoinCategory object
//is the only way that the appDelegate will save the information
self.coinsByCategory[i].index = Int16(i)
}
if let appDelegate = UIApplication.shared.delegate as? AppDelegate
{
appDelegate.saveContext()
}
}
//these delegate methods control the core data database
func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>)
{
tableView.beginUpdates()
}
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?)
{
switch type
{
case .insert :
if let newIndexPath = newIndexPath
{
tableView.insertRows(at: [newIndexPath], with: .fade)
}
case .delete:
if let indexPath = indexPath
{
tableView.deleteRows(at: [indexPath], with: .fade)
}
case .update:
if let indexPath = indexPath
{
tableView.reloadRows(at: [indexPath], with: .fade)
}
default:
tableView.reloadData()
}
if let fetchedObjects = controller.fetchedObjects
{
self.coinsByCategory = fetchedObjects as! [CoinCategoryMO]
}
}
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>)
{
tableView.endUpdates()
if self.isCurrentlyResortingCoinsIntoNewCategories != true
{
//we let the user know if the collection is empty
if self.coinsByCategory.count == 0
{
self.messageUserIfCollectionEmpty()
}
else
{
self.activateCollectionEmptyLabel(newState: false)
}
}
}
And then my CoinTableViewCell class is:
// Represents a cell of the coin buttons
import UIKit
class CoinTableViewCell: UITableViewCell {
#IBOutlet var countryLabel: UILabel!
#IBOutlet var valueAndDenominationLabel: UILabel!
#IBOutlet var quantityLabel: UILabel!
#IBOutlet var denominationOnlyLabel : UILabel!
#IBOutlet var yearLabel : UILabel!
override func awakeFromNib() {
super.awakeFromNib()
// Initialization code
}
func restoreAllLabelsToCell()
{
//this is a function that is called when this cell is being initialized in the cellForRowAt method in a tableview..
//we want to make all the labels visible so that the previous usage of a reusable tableview cell does not affect this usage of the cell
countryLabel.isHidden = false
valueAndDenominationLabel.isHidden = false
quantityLabel.isHidden = false
denominationOnlyLabel.isHidden = false
yearLabel.isHidden = false
}
func configureLabelsForCategoryType(theType : NSString)
{
//in this function, we remove all the extra labels
//that contain information that does not relate to the general type of the category from the stack view
//For example, the year label is removed when the category is a country, as a year does not determine what category a coin falls into.
//we restore all the labels in this cell as we do not want the reusable cell's past usage
//which may have lead to a label dissappearing to carry over into this new usage of the cell
self.restoreAllLabelsToCell()
switch theType
{
case CoinCategory.CategoryTypes.COUNTRY_VALUE_AND_CURRENCY.rawValue:
//we do not need information about the coin's denomination (without its value) or the year
denominationOnlyLabel.isHidden = true
yearLabel.isHidden = true
//after we remove the labels, we now make the first label bold and black
valueAndDenominationLabel.font = UIFont.boldSystemFont(ofSize: self.valueAndDenominationLabel.font.pointSize)
valueAndDenominationLabel.textColor = UIColor.black
case CoinCategory.CategoryTypes.COUNTRY.rawValue:
//we do not need the information about the coin's value and denominations nor year
valueAndDenominationLabel.isHidden = true
denominationOnlyLabel.isHidden = true
yearLabel.isHidden = true
//after we remove the labels, we make the first label bold and black
countryLabel.font = UIFont.boldSystemFont(ofSize: self.countryLabel.font.pointSize)
countryLabel.textColor = UIColor.black
case CoinCategory.CategoryTypes.CURRENCY.rawValue:
//we do not information about the coin's value & denomination (together, that is), or year
valueAndDenominationLabel.isHidden = true
yearLabel.isHidden = true
//after we remove the labels, we make the first label bold and black
denominationOnlyLabel.font = UIFont.boldSystemFont(ofSize: self.denominationOnlyLabel.font.pointSize)
denominationOnlyLabel.textColor = UIColor.black
case CoinCategory.CategoryTypes.YEAR.rawValue:
//we do not information about the coin's value, denomination, or country
valueAndDenominationLabel.removeFromSuperview()
denominationOnlyLabel.isHidden = true
countryLabel.isHidden = true
//after we remove the labels, we make the first label bold and black
yearLabel.font = UIFont.boldSystemFont(ofSize: self.yearLabel.font.pointSize)
yearLabel.textColor = UIColor.black
default:
//the string does not match any of the categories available
//we do not remove any labels
break
}
}
}
My CoreData implementation is a collection of CoinCategoryMO objects which have the property "Index" (for their position in the uitableviewcontroller) and a CoinCategory object which holds objects of the Coin Class.
I have been trying to debug this for several days now, and I have no idea what is going wrong. Could anyone please help?
Many many thanks in advance, and have a great day!
I guess, CategoryType in category.coinCategory?.currentCategoryType is not same across all objects in searchResults / coinsByCategory.
i.e. 2nd and 3rd objects has COUNTRY_VALUE_AND_CURRENCY as its currentCategoryType and 4th and 5th has COUNTRY.
Can you confirm that currentCategoryType is same for all objects in searchResults / coinsByCategory?
I think I know what the error is now:
In my configureLabelsForCategoryType method for my CoinTableViewCell class, I had invoked the removeFromSuperView() method on the valueAndDenomination label, which had the effect of permanently removing that label from the cell.
Thus the cell did not have that label, even if it was later reused for another CoinCategory.
I replaced the valueAndDenominationLabel.removeFromSuperView() line with valueAndDenominationLabel.isHidden = true which has the effect of hiding the valueAndDenominationLabel from the user, but not permanently removing it from the cell.
Many many thanks to those who took the time to read my question and to respond.
Your efforts helped me think about my problem and track it down!
Thank you!

How to get the indexPath of the current cell

I have currently trying to create a way to delete an item in a collection view at the indexPath of 1 back. So far i have used some help to create a function with scrollview did scroll to create a way to count which image the user is on by the current image method. I now need a way to count which cell the user is on. Here is my code>
var currentImage = 0
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let x = floor(myCollectionView.contentOffset.x / view.frame.width)
if Int(x) != currentImage {
currentImage = Int(x)
//print(currentImage)
}
if currentImage > 0 {
for collectionCell in myCollectionView.visibleCells as [UICollectionViewCell] {
let indexPath = myCollectionView.indexPath(for: collectionCell as UICollectionViewCell)!
let indexPathOfLastItem = (indexPath?.item)! - 1
let indexPathOfItemToDelete = IndexPath(item: (indexPathOfLastItem), section: 0)
imageArray.remove(at: 0)
myCollectionView.deleteItems(at: [indexPathOfItemToDelete])
currentImage = 1
Based more on the comments than your actual question, what you seem to want is to get the first visible cell's index path so you can use that path to delete the cell.
let visibleCells = myCollectionView.visibleCells
if let firstCell = visibleCells.first() {
if let indexPath = myCollectionView.indexPath(for: collectionCell as UICollectionViewCell) {
// use indexPath to delete the cell
}
}
None of this should be used or done in the scrollViewDidScroll delegate method.
[Updated for Swift 5.2] Here's a slightly more succinct way than #rmaddy's answer (but that one works just fine):
guard let indexPath = collectionView.indexPathsForVisibleItems.first else {
return
}
// Do whatever with the index path here.

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