I am building an iOS app and I am trying to implement a pull-down refresh control on my project. The data is fetched correctly from an API and displayed on my table. But the problem rises when I do pull down to refresh. The following situations happen:
If I pull down for a long distance from the top, and the tableview.reloadData() function is called, the cells in the non-visible portion of the table come with the default tableview cells on top of them, overlapping...
if I pull down multiple times in quick succession the same issue happens.
I believe that it is because tableview.reloadData() is called multiple times in quick succession. But why are the default cells getting dequeued on top of my custom cells? Here is the section of code in the function to handle the pulldown:
#objc func refreshFunc(){
//let offset = scrollView.contentOffset.y
if myRefreshControl.isRefreshing{
readJson { (activities) in
self.activities = activities
self.tableView.reloadData()
self.myRefreshControl.endRefreshing()
}
}
}
Any help would be appreciated. Thanks in advance
UPDATE:
Changing the code to the code below seems to remove the error, but the problem is that now I need to pull down twice in order to get the results updated on the table:
#objc func refreshFunc(){
readJson { (activities) in
self.activities = activities
}
self.tableView.reloadData()
self.myRefreshControl.endRefreshing()
}
Please note that running the reloadData on the main thread gives the same result, I still need to pull down twice to update.
Please try to give some delay before refresh table view may it resolve your problem.
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + delayTime) { [weak self] in
self?.tableView.reloadData()
}
Hope it works
Cheers :)
DispatchQueue.main.async {
self.tableView.reloadData
}
Try this, always, if u want change UI you have to call on main thread
Related
I have this problem where (in several places) after executing an API call, the view does not refresh until a user action - like a btn click, tab bar switch, etc occurs. I have a feeling it is related to threading, but I can't seem to figure it out and I am new to iOS programming. I have tried different solutions with DispatchQueue etc, using it, and not using it. Trying to call setNeedsDisplay on the controller view. But no luck yet. The following is an example of code pulled right from one of my tab bar item view controllers:
func getEmployeeUpdates(){
self.showLoader()
APIAdaptor.shared.getEmployeeUpdates(forEmployee: Session.shared.employee, completion: {
(updates:[ScheduleUpdate]?, error:Error?) in
guard error == nil else{
DispatchQueue.main.async {
// self.resetMainScreen()
self.hideLoader();
}
return
}
DispatchQueue.main.async {
self.hideLoader();
self.ScheduleUpdates = updates!
self.tableView.reloadData();
}
})
}
func showLoader(){
NSLayoutConstraint.activate([
activityIndicator!.centerXAnchor.constraint(equalTo: self.tableView.centerXAnchor),
activityIndicator!.centerYAnchor.constraint(equalTo: self.tableView.centerYAnchor)])
activityIndicator?.startAnimating();
}
func hideLoader(){
print("Hiding");
activityIndicator?.stopAnimating()
}
I have attached two images. The first image is where the api call has finished (confirmed through testing) but the view is not refreshing. The loader is frozen. It should disappear after a call to hideLoader(). the second Image is after a click, or tab bar item switch.
I should also mention that in this example, as well as in other api calls the view will refresh eventually after completing, but only after a significant delay.
If anyone can help I would appreciate it very much!
This was a problem caused by the simulator on Xcode 10.1. If you run into this problem, try updating Xcode, or using a real device.
I'm trying to implement a tableView that has 4 different possible prototype cells. They all inherit from base UITableViewCell class and implement its protocol.
For two of the cells there's asynchronous data fetching but one in particular has been giving me fits. The flow is as follows:
1) Dequeue reusable cell
2) Call configure
func configure(someArguments: ) {
//some checks
process(withArguments: ) { [weak self in] in
if let weakSelf = self {
weakSelf.reloadDelegate.reload(forID: id)
}
}
}
3) If the async data is in the cache, configure the cell using the image/data/stuff available and be happy
4) If the async data is NOT in the cache, fetch it, cache it, and call the completion
func process(withArguments: completion:) {
if let async_data = cache.exists(forID: async_data.id) {
//set labels, add views, etc
} else {
fetch_async_data() {
//add to cache
//call completion
}
}
}
5) If the completion is called, reload the row in question by passing the index path up to the UITableViewController and calling reloadRows(at:with:)
func reload(forID: ) {
tableView.beginUpdates()
tableView.reloadRows(at: indexPath_matching_forID with: .automatic)
tableView.endUpdates()
}
Now, my understanding is that reloadRows(at:with:) will trigger another dataSource/delegate cycle and thus result in a fresh resuable cell being dequeued, and the configure method being called again, thereby making step #3 happy (the async data will now be in the cache since we just fetched it).
Except...that's not always happening. If there are cells in my initial fetch that require reloading, it works - they get the data and display it. Sometimes, though, scrolling down to another cell that requires fetching DOES NOT get the right data...or more specifically, it doesn't trigger a reload that populates the cell with the right data. I CAN see the cache being updated with the fresh data, but it's not...showing up.
If, however, I scroll completely past the bad cell, and then scroll back up, the correct data is used. So, what the hell reloadRows?!
I've tried wrapping various things in DispatchQueue.main.async to no avail.
reloadData works, ish, but is expensive because of potentially many async requests firing on a full reload (plus it causes some excessive flickering as cells come back)
Any help would be appreciated!
Reused cells are not "fresh". Clear the cell while waiting for content.
func process(withArguments: completion:) {
if let async_data = cache.exists(forID: async_data.id) {
//set labels, add views, etc
} else {
fetch_async_data() {
// ** reset the content of the cell, clear labels etc **
//add to cache
//call completion
}
}
}
I have a tableView inside a collectionViewCell and I get an error when I try to reload the data.
*** Assertion failure in -[UITableView _endCellAnimationsWithContext:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-3600.6.21/UITableView.m:1610
I tried using Dispatch.main.async and it seems to get rid of the problem. The only thing is that it doesn't reload the data and nothing changes in the tableView
func cleanItems(completion: #escaping (Bool) -> Void) {
Dispatch.main.async {
cell.tableView.beginUpdates()
// Make changes in the Data Source
cell.tableView.deleteRows(at: selectedItems, with: .fade)
cell.tableView.endUpdates()
// Reloading sections accordingly depending on what the user has deleted
// Do I need to reload data here again? It used to work without Dispatch, but it wasn't stable
cell.tableView.reloadData()
// Updating items with if statements to reload data in Firebase
completion(true)
}
}
This doesn't reload the data at all and nothing seems to change. The good thing is that I don't get a random crash, which was the case before implementing Dispatch.main.async
I've retrieved the numberOfRows in each section to see how many rows there are after ending updates.
print(cell.tableView.numberOfRows(inSection: 1))
and I get the same number of rows that are in the current view.
This is crucial, because if the tableView sections are all zero, the collectionViewCell should disappear. And we never get here in the completion block as it says that the numberOfRows has never changed. Leaving us with a non updated tableView.
I solved this by moving Dispatch.main.async outside the function call.
Dispatch.main.async {
cleanItems(completion: { (success) in
etc.
})
}
I'm using background thread for getting my data from the network and main thread for presenting my cells:
dispatch_async(dispatch_get_global_queue(QOS_CLASS_BACKGROUND, 0), {
let _ = self.http.getInfo() { (result) in
self.cellsArray = result
dispatch_async(dispatch_get_main_queue(), {
self.tableView.reloadData()
})
completion(completed: true)
}
})
where self.http.getInfo is a NSURLSession.sharedSession().dataTaskWithRequest method for taking my network infos.
And when I run my app my cells start showing separately as: the first appears, in a second the next one appears, in 2 seconds the next one and etc.
Why they do not appear at the same time? And also, because of the background and main thread using, my UITableView jumps when I implement infinite scroll and append new cells to exist cell array.
How can I fix it?
write self.tableView.reloadData() this statement in completion handler of NSURLSession.sharedSession().dataTaskWithRequest.
Is there a way to increase the width of the section index titles displayed along the edge of a table view? In my current code some of the titles are being clipped on the left and right:
I'm not doing anything special in creating the list, just returning an NSArray filled with sorted NSStrings.
I had the same problem with my section index titles.
Not sure if this is the correct way, what worked for me was adding:
[self.tableView layoutIfNeeded];
before calling
[self.tableView reloadData];
jb
Fixed.
Turns out it's enough to return a single empty string the first time sectionIndexTitlesForTableView: is called, even if the real titles (when the data eventually arrives and the table is reloaded) will be wider.
Only if the initial call returns an empty list does the column for section index titles fail to adjust its width to fit the titles when they arrive.
Reload TableView and it should fix the issue,
override func viewDidLoad()
{
super.viewDidLoad()
self.tableView.reloadData()
}
iOS 8
I have that problem in iOS8 too.
This seems to be a bug in iOS8, which is not corrected at the time this post is written (10/2014).
Searching around I found two workarounds.
The first one is to force a reload of the data in the viewDidAppear. This will also correct the problem of self-sizing cells not working on first load.
override func viewDidAppear(animated: Bool) {
super.viewDidAppear(animated)
self.tableView.reloadData()
}
However in my case it was not solving the issue because I used to change the section index titles after viewDidAppear
So the second workaround is simply to realoadData() twice
self.tableView.reloadData()
self.tableView.reloadData()