I am attempting to update a data object that holds the data for my collectionView (simply just filtering the data model), and the wishing to reload the collectionView with the filtered data. The issue is upon reloading the collectionView I am getting and error indexPath out of range when the reload happens. Seems when debugging that the collectionView is attempting to reload the original dataObject, not the filtered one. What am I doing wrong:
func handleFilterAction(sender: FilterButton){
guard let type = sender.buttonFilterType else {return}
switch type {
case .FilterAll:
return
case .FilterDay:
return
case .FillterWeek:
return
case .FilterMonth:
collectionView?.performBatchUpdates({
let objects = FilterDataManager.filterDataWith(currentLocalData: &self.eventObjects, filterOption: .ThisMonth)
self.eventObjects.removeAll()
self.eventObjects = objects
}, completion: { (completion) in
self.navigationItem.title = "This Month"
self.collectionView?.reloadData()
})
}
self.handleShowFilterView()
}
The eventObjects is what the collectionView should be reading for the data:
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return eventObjects[section].sectionObjects.count
}
You call performBatchUpdates when you want to animate the changes to the collectionView. iOS expects you to make calls to methods such as collectionView?.insertItems(at: [IndexPath]) and
collectionView?.deleteItems(at: [IndexPath]) to let it know what you are inserting and deleting so that it can animate it. For both of these calls, you pass in an array of all of the IndexPaths being inserted or deleted.
When you do this, iOS has expectations for the number of items that are now in the collectionView. The formula is:
newItemCount = previousItemCount - deletedItemCount + insertedItemCount
In your case, you modified your model, but you never called the insertItems and deleteItems methods, so iOS still thinks all of the items are there. It is this disconnect between your model and the collectionView that is causing your problem.
To fix this, you need to do one of the following:
Call deleteItems and insertItems with the array of IndexPaths that you are deleting and inserting (call delete first).
Or, forget about performBatchUpdates and just update your model data and call reloadData.
Also, make sure numberOfSections is returning eventObjects.count.
Related
My app uses a UITableView to implement a TikTok-style UX. Each cell is the height of the entire screen. Pagination is enabled, and this works fine for the first batch of 10 records I load. Each UITableViewCell is one "page". The user can "flip" through the pages by swiping, and initially each "page" fully flips as expected. However when I add additional rows by checking to see if the currently visible cell is the last one and then loading 10 more rows, the pagination goes haywire. Swiping results in a partially "flipped" cell -- parts of two cells are visible at the same time. I've tried various things but I'm not even sure what the problem is. The tableView seems to lose track of geometry.
Note: After the pagination goes haywire I can flip all the way back to the first cell. At that point the UITableView seems to regain composure and once again I'm able to flip correctly through all of the loaded rows, including the new ones.
func tableView(_ tableView: UITableView, didEndDisplaying cell: UITableViewCell, forRowAt indexPath: IndexPath) {
// Pause the video if the cell is ended displaying
if let cell = cell as? HomeTableViewCell {
cell.pause()
}
if let indices = tableView.indexPathsForVisibleRows {
for index in indices {
if index.row >= self.data.count - 1 {
self.viewModel!.getPosts()
break
}
}
}
}
In order to create a "Tik Tok" style UX, I ended up using the Texture framework together with a cloud video provider (mux.com). Works fine now.
I was facing the same issue and as I couldn't find a solution anywhere else here's how I solved it without using Texture:
I used the UITableViewDataSourcePrefetching protocol to fetch the new data to be inserted
extension TikTokTableView: UITableViewDataSourcePrefetching {
func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
viewModel.prefetchRows(at: indexPaths)
}
}
prefetchRows will execute the request if the visible cell is the last one, as in my case
func prefetchRows(at indexPaths: [IndexPath]) {
if indexPaths.contains(where: isLastCell) {
getPosts(type: typeOfPosts, offset: posts.count, lastPostId: lastPost)
}
}
private func isLastCell(for indexPath: IndexPath) -> Bool {
return indexPath.row == posts.count - 1
}
I have a weak var view delegate type TikTokTableViewDelegate in my view model to have access to a function insertItems implemented by my TikTokTableView. This function is used to inform the UITableView where to insert the incoming posts at
self.posts.append(contentsOf: response.posts)
let indexPathsToReload = self.calculateIndexPathToReload(from: response.posts)
self.view?.insertItems(at: indexPathsToReload)
private func calculateIndexPathToReload(from newPosts: [Post]) -> [IndexPath] {
let startIndex = posts.count - newPosts.count
let endIndex = startIndex + newPosts.count
print(startIndex, endIndex)
return (startIndex..<endIndex).map { IndexPath(row: $0, section: 0) }
}
and this is the insertItems function implemented in TikTokTableView and here is the key: If we try to insert those rows, the pagination of the table will fail and leave that weird offset, we have to store the indexPaths in a local property and insert them once the scroll animation has finished.
extension TikTokTableView: TikTokTableViewDelegate {
func insertItems(at indexPathsToReload: [IndexPath]) {
DispatchQueue.main.async {
// if we try to insert rows in the table, the scroll animation will be stopped and the cell will have a weird offset
// that's why we keep the indexPaths and insert them on scrollViewDidEndDecelerating(:)
self.indexPathsToReload = indexPathsToReload
}
}
}
Since UITableView is a subclass of UIScrollView, we have access to scrollViewDidEndDecelerating, this func is triggered at the end of a user's scroll and this is the time when we insert the new rows
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
if !indexPathsToReload.isEmpty {
tableView.insertRows(at: indexPathsToReload, with: .none)
indexPathsToReload = []
}
}
I'm using RxDataSources to load and display a UITableview. I am trying to update the section header with the amount of items that it holds, however tough the cell and items update correctly, the title remains stale.
This is my code for the DataSource object:
tableViewDataSource = RxTableViewSectionedAnimatedDataSource<TableViewParticipationSection>(
configureCell: { (_, tableView, _, item) in
return TableViewCellType.transformData(item).cell(inTableView: tableView)
}, titleForHeaderInSection: { dataSource, index in
let sectionModel = dataSource.sectionModels[index]
return "\(sectionModel.items.count)"
})
The identity of the section header is just {return 0} since I only have a single section.
Furthermore I have confirmed that if I use this code:
DispatchQueue.main.asyncAfter(deadline: .now()+3, execute: {
self?.contentView.tableView.reloadData()
})
It will actually update the section title, so it seems to be some problem with staleness but I can't seem to track it down.
Does anyone have experience with dynamic titles using RxDataSources
Edit:
After further experiments, the title will update, if I scroll around in the tableview, the title changes at some point.
Turns out that the title or any data on the section model is not included in the diff, so no matter what you do, it won't make a difference. The RxDataSource doesn't support non static headers. The solution is to make a custom view and do the binding myself.
In my case I set new empty UIView for section in
func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
if section == 0 {
let customHeaderViewMulti = tableView.dequeueReusableHeaderFooterView(withIdentifier: "CustomHeaderView") as! CustomHeaderView
return customHeaderView
}
// This is WRONG:
return UIView()
}
You must return nil for other cases.
Its getting called in viewDidLoad, after fetching the data used.
After some print debugging it looks like it calls all the appropriate delegeate methods, if no data is changed. If there has been some data changed, cellForItemAt does not get called.
Reloading the whole section works fine. But gives me an unwanted animation. Tried disabling UIView animation before, and enabling after reloading section, but still gives me a little animation.
collectionView.reloadSections(IndexSet(integer: 0))
Here is my current situation, when using reloadData()
The UICollectionViewController is a part of a TabBarController.
I'm using custom UICollectionViewCells. The data is loaded from CoreData.
First time opening the tab, its works fine.
After updating the favorites item in another tab, and returning to this collectionView, its not updated. But if i select another tab, and go back to this one, its updated.
var favorites = [Item]()
override func viewWillAppear(_ animated: Bool) {
collectionView!.register(UINib.init(nibName: reuseIdentifier, bundle: nil), forCellWithReuseIdentifier: reuseIdentifier)
if let flowLayout = collectionView!.collectionViewLayout as? UICollectionViewFlowLayout {
flowLayout.estimatedItemSize = CGSize(width: 1,height: 1)
}
loadFavorites()
}
func loadFavorites() {
do {
print("Load Favorites")
let fetch: NSFetchRequest = Item.fetchRequest()
let predicate = NSPredicate(format: "favorite == %#", NSNumber(value: true))
fetch.predicate = predicate
favorites = try managedObjectContext.fetch(fetch)
if favorites.count > 0 {
print("Favorites count: \(favorites.count)")
notification?.removeFromSuperview()
} else {
showEmptyFavoritesNotification()
}
print("Reload CollectionView")
collectionView!.reloadData(
} catch {
print("Fetching Sections from Core Data failed")
}
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
print("Get number of section, \(favorites.count)")
if favorites.count > 0 {
return favorites.count
} else {
return 0
}
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
print("Get cell")
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! SubMenuCell
let menuItem = favorites[indexPath.row]
cell.title = menuItem.title
cell.subtitle = menuItem.subtitle
return cell
}
Console Print/Log
Starting the app, going to the CollectionView tab where there are no favorites:
Load Favorites
Get number of section, 0
Get number of section, 0
Reload CollectionView
Get number of section, 0
Switching tab, and adding and setting an Item object's favorite to true, then heading back to the CollectionView tab:
Load Favorites
Favorites count: 1
Reload CollectionView
Get number of section, 1
The datamodel has 1 item, reloading CollectonView, cellForRowAtIndex not called?
Selecting another tab, random which, then heading back to the CollectionView tab, without changing any data.
Load Favorites
Favorites count: 1
Reload CollectionView
Get number of section, 1
Get cell
Now my Item shows up in the list. You can see from the Get Cell that cellForItemAt is called aswell. Nothing has changed between these last two loggings, just clicked back/fourth on the tabs one time.
Forgot to mention, but this code IS working fine in the simulator.
On a read device its just not giving me any error, just not showing the cell (or calling the cellForItemAt)
After some more debugging i got an error when the items got reduced (instead of increasing like i've tried above).
UICollectionView received layout attributes for a cell with an index path that does not exist
This led med to iOS 10 bug: UICollectionView received layout attributes for a cell with an index path that does not exist
collectionView!.reloadData()
collectionView!.collectionViewLayout.invalidateLayout()
collectionView!.layoutSubviews()
This solved my problem.
I am using autoresizing cells, but i guess this does not explain why cellForItemAt did not get called.
in my case, my collectionview was in a stackview, i didnt make any constraints, when i added the necessary constraints it worked.
Just check collectionview's constraints.
Ok, maybe I can help someone =)
I do this:
Load data from API
Then after load data call DispatchQueue.main.async like this
DispatchQueue.main.async {
self.pointNews = pointNews
}
In self.pointNews didSet I try to do collectionView.reloadData(), but it work only, if I call DispatchQueue.main.async in didSet
DispatchQueue.main.async {
self.collectionView.reloadData()
}
var paths: [IndexPath] = []
if !data.isEmpty {
for i in 0...salesArray.count - 1 {
paths.append(IndexPath(item: i, section: 0))
}
collectionView.reloadData()
collectionView.reloadItems(at: paths)
}
This is the code helped me, for solving this kind of issue.
Post your code.
One possibility is that you are using `URLSession and trying to tell your collection view to update from the it's delegate method/completion closure, not realizing that that code is run on a background thread and you can't do UI calls from background threads.
I faced the same problem with self resizing cells and above solution works as well but collection view scroll position resets and goes to top. Below solution helps to retain your scroll position.
collectionView.reloadData()
let context = collectionView.collectionViewLayout.invalidationContext(forBoundsChange: collectionView.bounds)
context.contentOffsetAdjustment = CGPoint.zero
collectionView.collectionViewLayout.invalidateLayout(with: context)
collectionView.layoutSubviews()
i was facing also this kind of issue so finally i am able to solved using this line of code
[self.collectionView reloadData];
[self.collectionView reloadItemsAtIndexPaths:#[[NSIndexPath indexPathWithIndex:0]]];
I had the same issue. I was updating the height of the UICollectionView based on the content and reloadData() stops working when you set the height of the collection view to zero. After setting a minimum height. reloadData() was working as expected.
I actually want to create table with rows and columns and doing this using UICollectionView. Problem is with reloading or updating collectionView to add or delete rows in my table. Columns and hardcoded i-e 4.
This is how i am doing;
Creating CollectionView from storyboard
After loading page. Hitting route to get data
After fetching data save the fetched data in an array object.
Update collection view with the size of the array by collectionView.reloadData().
Starting here.
Referring collection view from storyboard to my viewController
#IBOutlet weak var collectionView: UICollectionView!
then in "viewDidLoad".
self.collectionView.delegate = self
self.collectionView.dataSource = self
Now after getting response from server. I am updating my Array from which i get number of rows to create. After that This is how i am reloading collectionView.
DispatchQueue.main.async
{
self.collectionView.collectionViewLayout.invalidateLayout()
self.collectionView.reloadData()
print("size of the array is(self.portfolioHandler.data.count)")
}
In my numberOfSections function. i am getting correct number of cells to create. returning as well.
func numberOfSections(in collectionView: UICollectionView) -> Int {
var toReturn : Int = 1
if (self.portfolioHandler != nil) {
let data : [PortfolioData] = self.portfolioHandler.data!
print("dataCount : \(data.count)")
toReturn = data.count + 1
print("toReturn : \(toReturn)")
}
return toReturn
}
With logs i am getting the returned number. it is correct and returning data correctly.
Now in my cellForItem At index function. IndexPath is not updating. it is still 1. the top header i am creating. No Cell beneath it.
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "MyCell", for: indexPath) as! MyCollectionViewCell
print("section: \(indexPath.section) && row: \(indexPath.row)")
After everything i tried. Nothing helps me to get the correct cells to create in my collectionView.
A trick can work. Only if i give hardcoded value in numberOfSections in start. Then after server response and reloading collectionView it will create those number of cells like 3 or 4 what i hardcoded above. No more then that.
But i have to create number of cells which i get from server. Dynamic.
I have spent much time on it. Please help me where i am wrong. or how i can resolve this.
After all attempts. I am unable to solve this reload issue of collection view.
But I handle this in my app by this trick
collection view first time make cells correctly. problem is with reloading. So i made my server request in previous View Controller before coming to this View Controller. And sending the response to this View Controller. This way. i have number of cells to made. So it worked.
But as a learner i am looking forward for an answer and real solution to this reload issue problem.
I will appreciate that. Although thanks #ɯɐɹʞ for your comments.
I have a TableView in my app that when user tap the button in one of the cells the safari will open in the app and when the safari dismiss the app will crash because I want to update one of the parameters in the tableview so I need to remove all and append them again from Json But this will take some seconds so the app will crash because there is no data to show I used Timer But timer is not good solution because some times it will take more time than timer so it will crash again I need a method that wait to finish and then do some thing else of if you think this is not a good solution too please guide me which solution is good for this problem
here is what I used in my app after dismiss safari in application(its not all of the codes but these codes has problems )
if let payed = dict.value(forKey: "payed"){
factorViewController.payed.removeAll()
self.factorTableView.reloadData()
factorViewController.payed.append(payed as! Int)
self.factorTableView.reloadData()
print("payed = \([payed])")
}
Try reloading the data only once:
if let payed = dict.value(forKey: "payed") {
// Empty Array here
factorViewController.payed.removeAll()
// You are appending here, so array will not be empty
factorViewController.payed.append(payed as! Int)
// Now you can reload data
self.factorTableView.reloadData()
print("payed = \([payed])")
// Also, if this doesn't work, you can use a callback(completion handler).
}
That way, your array will not be empty when you need to reload data
How TableView Works
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return your_array.count // It returns how much cells you want in your tableview.
}
// This func defines what you wanted in your cell
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = dequeue_property // to dequeue your cell
your_lbl.text = your_array[indexpath.row] // as per logic
return cell
}
In your case
Count of array in numberOfRowsInSection is more than the array you'r using in the cellForRowAt so on dequeue your cell have more index than the array you are using in cellForRow. Thats why is doesn't getting index and crashes with IndexOutOFRange
You have array issue not tableView Reload issue
Take ref : Swift array always give me "fatal error: Array index out of range"
Ok That was easier than I thought ! I just defined another variables in my app and when started getting Json append new data to the new variables and then equals new variables to old variables ! thats it!