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I am using a UITableViewController and need to reload the table within a function. When I run the app the table view is not reloading. I am receiving no errors.
CODE:
func loadTheaters() {
let api = ""
let theaterId = id
let date = date
let url = URL(string: "http://data.tmsapi.com/v1.1/theatres/\(theaterId)/showings?startDate=\(date)&api_key=\(api)")
print(url!)
let request = URLRequest(
url: url! as URL,
cachePolicy: URLRequest.CachePolicy.reloadIgnoringLocalCacheData,
timeoutInterval: 10 )
let session = URLSession (
configuration: URLSessionConfiguration.default,
delegate: nil,
delegateQueue: OperationQueue.main
)
let task = session.dataTask(with: request, completionHandler: { (dataOrNil, response, error) in
if let data = dataOrNil {
do { let filmList = try! JSONDecoder().decode([Films].self, from: data)
self.films = filmList
self.tableView.reloadData()
}
}
})
task.resume()
}
Why is the tableview not reloading?
I had numberOfSections returned to 0.
Solved:
override func numberOfSections(in tableView: UITableView) -> Int {
// #warning Incomplete implementation, return the number of sections
return 1
}
You should reload tableView in the main queue,
DispatchQueue.main.async {
self.tableView.reloadData()
}
post this please check your numberOfSections and numberOfRowsInSection dataSource methods if they are handled properly
Related
I'm currently implementing an App which has a collectionView. The cells in the collection view are filled via an API-request. The requests are to the same API but with different locations. So for example for the first cell I'm calling: "google.de/GamesInItaly" and for the second cell: "google/GamesInGermany". While I'm scrolling down the collectionView the appearing cells should also make an API-request that has different countries.
The Problem I'm facing is, that I don't know how to handle the different API calls.
I managed to make one API-request and fill every cell with the same data, but I want different data for every cell.
My code looks like this:
CollectionView:
Call with from collectionView:
func fetchMatch() {
ApiService.sharedInstance.fetchGames(from: contentURL, completion: { (content: [[contentModel]]) in
self.content = content
self.collectionView.reloadData()
})
}
API-Services:
Set the Url:
func fetchGames(from url: String, completion: #escaping ([contentModel]) -> ()) {
fetchFeedForUrlString(urlString: "\(BaseUrl)/getgames/\(url)", completion: completion)
}
Fetch function:
func fetchFeedForUrlString<T: Decodable>(urlString: String, completion: #escaping (T) -> ())
{
let url = URL(string: urlString)
let task = URLSession.shared.dataTask(with: url!) { (data, response, error) in
guard let data = data else {
return
}
do {
let json = try JSONDecoder().decode(T.self, from: data)
DispatchQueue.main.async {
completion(json)
}
} catch let jsonError {
print(jsonError)
}
}
task.resume()
}
I think what I could do is make many of these fetchGames functions, but I think that would be a bad practice.
I've also read about DispatchGroup but I'm not really sure how I can implement these into my program.
Does somebody know how I can handle multiple API-calls in a good practice?
I have to populate a TableView with some data fetched with an URLSession task. The source is an XML file, so i parse it into the task. The result of parsing, is an array that i pass to another function that populate another array used by TableView Delegates.
My problem is that TableView Delegates are called before task ends, so tha table is empty when i start the app, unless a data reloading (so i know that parsing and task work fine).
Here is viewDidLoad function. listOfApps is my TableView
override func viewDidLoad() {
super.viewDidLoad()
fetchData()
checkInstalledApps(apps: <ARRAY POPULATED>)
listOfApps.delegate = self
listOfApps.dataSource = self
}
}
fetchData is the function where i fetch the XML file and parse it
func fetchData() {
let myUrl = URL(string: "<POST REQUEST>");
var request = URLRequest(url:myUrl!)
request.httpMethod = "POST"
let postString = "firstName=James&lastName=Bond";
request.httpBody = postString.data(using: String.Encoding.utf8);
let task = URLSession.shared.dataTask(with: request) { (data: Data?, response: URLResponse?, error: Error?) in
self.parser = XMLParser(data: data!)
self.parser.delegate = self
}
task.resume()
}
while checkInstalledApps is the function where i compose the array used by TableView Delegates.
func checkInstalledApps(apps: NSMutableArray){
....
installedApps.add(...)
installedApps.add(...)
....
}
So, for example, to set the number of rows i count installedApps elements
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
if (installedApps.count == 0) {
noApp = true
return 1
}
return installedApps.count
}
that are 0. Obviously, if i reload data, it's all ok.
My problem is the async call: first of that i used an XML accessible via GET request, so i can use XMLParser(contentsOf: myUrl) and the time is not a problem. Maybe if the XML will grow up, also in this way i will have some trouble, but now i've to use a POST request
I've tried with DispatchGroup, with a
group.enter() before super.viewDidLoad
group.leave() after task.resume()
group.wait() after checkInstalledApps()
where group is let group = DispatchGroup(), but nothing.
So, how can i tell to the tableview delegate to wait the task response and the next function?
thanks in advance
I would forget about DispatchGroup, and change a way of thinking here (you don't want to freeze the UI until the response is here).
I believe you can leave the fetchData implementation as it is.
In XMLParserDelegate.parserDidEndDocument(_:) you will be notified that the XML has been parsed. In that method call checkInstalledApps to populate the model data. After that simply call listOfApps.reloadData() to tell the tableView to reload with the new data.
You want to call both checkInstalledApps and listOfApps.reloadData() on the main thread (using DispatchQueue.main.async {}).
Also keep listOfApps.delegate = self and listOfApps.dataSource = self in viewDidLoad as it is now.
The cleaner way is to use an empty state view / activityIndicator / loader / progress hud (whatever you want), informing the user that the app is fetching/loading datas,
After the fetch is done, just reload your tableview and remove the empty state view / loader
Your problem is caused by the fact that you currently have no way in knowing when the URLSession task ended. The reloadData() call occurs almost instantly after submitting the request, thus you see the empty table, and a later table reload is needed, though the new reload should be no sooner that the task ending.
Here's a simplified diagram of what happens:
Completion blocks provide here an easy-to-implement solution. Below you can find a very simplistic (and likely incomplete as I don't have all the details regarding the actual xml parsing) solution:
func fetchData(completion: #escaping () -> Void) {
let task = URLSession.shared.dataTask(with: request) { (data: Data?, response: URLResponse?, error: Error?) in
self.parser = XMLParser(data: data!)
self.parser.delegate = self
completion()
}
override func viewDidLoad() {
super.viewDidLoad()
fetchData() { [weak self] in self?.tableView.reloadData() }
}
Basically the completion block will complete the xml data return chain.
I have a UITableView with about 1000 rows. I also have a timer running every 6 seconds that fetches data from a web service. Each time I call reloadData() there is a blip - my app freezes very noticeably for a brief moment. This is very evident when scrolling.
I tried fetching about 400 rows only and the blip disappears. Any tips how to get rid of this while still fetching the 1000 rows?
var items: [Item] = []
Timer.scheduledTimer(withTimeInterval: 6, repeats: true) { [weak self] _ in
guard let strongSelf = self else { return }
Alamofire.request(urlString, method: method, parameters: params) { response in
// parse the response here and save it in array called itemsFromResponse
OperationQueue.main.addOperation {
strongSelf.items = itemsFromResponse
strongSelf.itemsTableView.reloadData()
}
}
}
UITableViewDataSource code:
extension ItemViewController: UITableViewDataSource, UITableViewDelegate {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return items.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "itemCell", for: indexPath)
cell.textLabel?.text = items[indexPath.row].name
return cell
}
}
The problem is being caused because you are storing the items from the response and then updating the table view from the same OperationQueue, meaning that the UI thread is being blocked while your array is being updated. Using an operation queue in itself is not an optimal way to schedule tasks if you do not need fine grain control over the task (such as cancelling and advanced scheduling, like you don't need here). You should instead be using a DispatchQueue, see here for more.
In order to fix your issue, you should update your array from the background completion handler, then update your table.
Timer.scheduledTimer(withTimeInterval: 6, repeats: true) { [weak self] _ in
guard let strongSelf = self else { return }
Alamofire.request(urlString, method: method, parameters: params) { response in
// parse the response here and save it in array called itemsFromResponse
strongSelf.items = itemsFromResponse
// update the table on the main (UI) thread
DispatchQueue.main.async {
strongSelf.itemsTableView.reloadData()
}
}
}
You should also maybe look into a more efficient way to fetch new data, because reloading the entire dataset every 6 seconds is not very efficient in terms of data or CPU on the user's phone.
The problem is you are reloading data every 6 seconds, so if the data is so big you're reloading 1000 rows every 6 seconds. I recommend you request the data and compare if there's new data so in that case you need to reload data or you simply ask to refresh once. For example:
var items: [Item] = []
Timer.scheduledTimer(withTimeInterval: 6, repeats: true) { [weak self] _ in
guard let strongSelf = self else { return }
Alamofire.request(urlString, method: method, parameters: params) { response in
// parse the response here and save it in array called itemsFromResponse
OperationQueue.main.addOperation {
if(strongSelf.items != itemsFromResponse){
strongSelf.items = itemsFromResponse
strongSelf.itemsTableView.reloadData()
}
}
}
I have a header view for every UITableViewCell. In this header view, I load a picture of an individual via an asynchronous function in the Facebook API. However, because the function is asynchronous, I believe the function is called multiple times over and over again, causing the image to flicker constantly. I would imagine a fix to this issue would be to load the images in viewDidLoad in an array first, then display the array contents in the header view of the UITableViewCell. However, I am having trouble implementing this because of the asynchronous nature of the function: I can't seem to grab every photo, and then continue on with my program. Here is my attempt:
//Function to get a user's profile picture
func getProfilePicture(completion: (result: Bool, image: UIImage?) -> Void){
// Get user profile pic
let url = NSURL(string: "https://graph.facebook.com/1234567890/picture?type=large")
let urlRequest = NSURLRequest(URL: url!)
//Asynchronous request to display image
NSURLConnection.sendAsynchronousRequest(urlRequest, queue: NSOperationQueue.mainQueue()) { (response:NSURLResponse!, data:NSData!, error:NSError!) -> Void in
if error != nil{
println("Error: \(error)")
}
// Display the image
let image = UIImage(data: data)
if(image != nil){
completion(result: true, image: image)
}
}
}
override func viewDidLoad() {
self.getProfilePicture { (result, image) -> Void in
if(result == true){
println("Loading Photo")
self.creatorImages.append(image!)
}
else{
println("False")
}
}
}
func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
//Show section header cell with image
var cellIdentifier = "SectionHeaderCell"
var headerView = tableView.dequeueReusableCellWithIdentifier(cellIdentifier) as! SectionHeaderCell
headerView.headerImage.image = self.creatorImages[section]
headerView.headerImage.clipsToBounds = true
headerView.headerImage.layer.cornerRadius = headerView.headerImage.frame.size.width / 2
return headerView
}
As seen by the program above, I the global array that I created called self.creatorImages which holds the array of images I grab from the Facebook API is always empty and I need to "wait" for all the pictures to populate the array before actually using it. I'm not sure how to accomplish this because I did try a completion handler in my getProfilePicture function but that didn't seem to help and that is one way I have learned to deal with asynchronous functions. Any other ideas? Thanks!
I had the same problem but mine was in Objective-C
Well, the structure is not that different, what i did was adding condition with:
headerView.headerImage.image
Here's an improved solution that i think suits your implementation..
since you placed self.getProfilePicture inside viewDidLoad it will only be called once section==0 will only contain an image,
the code below will request for addition image if self.creatorImages's index is out of range/bounds
func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
//Show section header cell with image
var cellIdentifier = "SectionHeaderCell"
var headerView = tableView.dequeueReusableCellWithIdentifier(cellIdentifier) as! SectionHeaderCell
if (section < self.creatorImages.count) // validate self.creatorImages index to prevent 'Array index out of range' error
{
if (headerView.headerImage.image == nil) // prevents the blinks
{
headerView.headerImage.image = self.creatorImages[section];
}
}
else // requests for additional image at section
{
// this will be called more than expected because of tableView.reloadData()
println("Loading Photo")
self.getProfilePicture { (result, image) -> Void in
if(result == true) {
//simply appending will do the work but i suggest something like:
if (self.creatorImages.count <= section)
{
self.creatorImages.append(image!)
tableView.reloadData()
println("self.creatorImages.count \(self.creatorImages.count)")
}
//that will prevent appending excessively to data source
}
else{
println("Error loading image")
}
}
}
headerView.headerImage.clipsToBounds = true
headerView.headerImage.layer.cornerRadius = headerView.headerImage.frame.size.width / 2
return headerView
}
You sure have different implementation from what i have in mind, but codes in edit history is not in vain, right?.. hahahaha.. ;)
Hope i've helped you.. Cheers!
I have a simple iOS application written in Swift that loads JSON data downloaded over the Internet and displays it into a UITableView. When I launch the application for the first time, everything works correctly and the table displays the correct information.
In my app, I have a button that triggers a refresh when I would like to reload the data. So I call the displayTable() method when the refresh button is tapped which downloads the data again and then calls the tableView.reloadData() method on the main thread to refresh the data but the reload does not appear to work. I manually change the data on the server and hit refresh but I still have the old data cached in my application. I can exit/kill the application and the old data stays 'stuck' forever unless I delete the app and reinstall.
I've attached the code for my ViewController below. I've spent way too many hours looking at this and I cannot seem to find why the reloadData doesn't work. Any ideas, hints would be greatly appreciated.
thanks
--Vinny
class ViewController: UITableViewController {
var tableData = []
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewWillAppear(animated: Bool) {
println("viewWillAppear was just called")
super.viewWillAppear(true)
self.displayTable()
}
func displayTable() {
getJSONData("http://www.example.com/data.json") { (results, resultError) in
if (resultError == nil) {
if var results = results {
dispatch_async(dispatch_get_main_queue(), {
self.tableData = [] //create out data on subsequent refreshes
self.tableData = results
self.tableView.reloadData() //This doesn't appear to be working!
})
} else {
self.displayErrorPopup()
}
} else {
self.displayErrorPopup()
}
}
}
func displayErrorPopup() {
let alertViewController = UIAlertController(title: "Error", message: "Couldn't connect to API", preferredStyle: .Alert)
let okButton = UIAlertAction(title: "OK", style: .Default, handler: nil)
let cancelButton = UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)
alertViewController.addAction(okButton)
alertViewController.addAction(cancelButton)
self.presentViewController(alertViewController, animated: true, completion: nil)
}
//todo - extract this method into it's own class
func getJSONData(ttAPIURL : String, completion: (resultsArray: NSArray?, resultError: NSError?) -> ()){
let mySession = NSURLSession.sharedSession()
let url: NSURL = NSURL(string: ttAPIURL)!
let networkTask = mySession.dataTaskWithURL(url, completionHandler : {data, response, error -> Void in
var err: NSError?
if (error == nil) {
var theJSON = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &err) as NSMutableDictionary
let results : NSArray = theJSON["list"]!["times"] as NSArray
completion(resultsArray: results, resultError: error)
} else {
completion(resultsArray: nil, resultError: error)
}
})
networkTask.resume()
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return tableData.count
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("ttCell", forIndexPath: indexPath) as UITableViewCell
let timesEntry = self.tableData[indexPath.row] as NSMutableDictionary
cell.textLabel.text = (timesEntry["routeName"] as String)
return cell
}
override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return 1
}
#IBAction func refreshButtonTap(sender: AnyObject) {
self.displayTable()
}
}
Ok, so you say that reloadData is not working but that is almost certainly not your problem. To debug this you should:
Make sure reloadData is actually being called (breakpoint or println)
Check if the UITableViewDataSource methods are being called after you call reloadData (breakpoint or println)
Check the results array that you are getting back from the network request (probably println(results))
My guess is that it is failing at number 3 which means it has nothing to do with reloadData. Perhaps the shared NSURLSession has caching enabled? Try setting mySession.URLCache to nil.
Try to replace it
override func viewWillAppear(animated: Bool) {
println("viewWillAppear was just called")
super.viewWillAppear(true)
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), { () -> Void in
self.displayTable()
})
}
Thanks drewag and Jirom for your answers. Great comments that were very helpful. I just found my problem and its something I should have thought about earlier. The domain which is hosting my dynamic JSON data is being protected by CloudFlare and it appears that my pages rules to disable caching for a certain directory aren't working. So all of the JSON content was being cached and that was the reason my application wouldn't show the new data.
Thanks again guys for your responses.
--Vinny
PS: Per Drewag's suggestion, I added an instance of NSURLSessionConfiguration which defines the behavior and policies to use when downloading data using an NSURLSession object, and set the URLCache property to nil to disable caching.
let config = NSURLSessionConfiguration.defaultSessionConfiguration()
config.URLCache = nil
let mySession = NSURLSession(configuration: config)