Problem: When using Alamofire and SwiftyJSON to populate a UITableView, the table view loads but there is a 1 second pause before the data is displayed. I am not sure where I should be calling reloadData() to fix this.
There are various questions about when to call reloadData() using Alamofire and SwiftyJSON to populate a UITableView, but I have yet to find an answer that solves my problem.
A bit of background:
I am using the Google Places Web API to populate a UITableView with Google Place names, addresses and icons. Originally I was only using SwiftyJSON to accomplish this, but it was taking quite some time for the UITableView to load. Here is some of that code:
GooglePlacesRequest.swift:
...
var placesNearbyArray: [GooglePlaceNearby]?
if let url = NSURL(string: urlString) {
if let data = NSData(contentsOfURL: url, options: .allZeros, error: nil) {
let json = JSON(data: data)
placesNearbyArray = parseNearbyJSON(json)
completion(placesNearbyArray)
} else {
completion(placesNearbyArray)
}
} else {
completion(placesNearbyArray)
}
}
func parseNearbyJSON(json: JSON) -> [GooglePlaceNearby] {
var placesNearbyArray = [GooglePlaceNearby]()
for result in json["results"].arrayValue {
let name = result["name"].stringValue
let address = result["vicinity"].stringValue
...
placesNearbyArray.append(place)
}
return placesNearbyArray
}
And the code from viewWillAppear in the UITableView:
override func viewWillAppear(animated: Bool) {
...
placesRequest.getPlacesNearUserLocation(location, completion: { (googlePlaces) -> Void in
if let googlePlaces = googlePlaces {
self.venues = googlePlaces
}
dispatch_async(dispatch_get_main_queue(), { () -> Void in
self.tableView.reloadData()
})
})
}
As I said above, this approach was working, but the UITableView would often take 3 - 4 seconds to load. I then decided to use Alamofire along with SwiftyJSON and (posssibly) a cache.
Here are some snippets of the current code:
GooglePlacesRequest.swift:
...
var placesNearbyArray: [GooglePlaceNearby]?
request(.GET, urlString).responseSwiftyJSON({ (_, _, json, error) in
var innerPlacesArray = [GooglePlaceNearby]()
for result in json["results"].arrayValue {
let name = result["name"].stringValue
let address = result["vicinity"].stringValue
...
innerPlacesArray.append(place)
}
placesNearbyArray = innerPlacesArray
completion(placesNearbyArray)
})
completion(placesNearbyArray)
}
After adding this, I tried to use the same code from viewWillAppear in the UITableView, but this is what happens:
The UITableView loads much faster
There is then a 1 second pause before the table view cells are populated.
I have tried to place the new request function in various places in the UITableView, such as in the viewDidLoad:
override func viewDidLoad() {
super.viewDidLoad()
...
let placesRequest = PlacesRequest()
placesRequest.fetchNearbyPlaces(location, completion: { (googlePlaces) -> Void in
if let googlePlaces = googlePlaces {
self.venues = googlePlaces
}
dispatch_async(dispatch_get_main_queue(), { () -> Void in
self.tableView.reloadData()
})
}
)
And I have also tried to call reloadData() on the main thread in both viewWillLoad and viewWillAppear.
The result is always the same...there is a 1 second pause before the UITableView loads the data.
Before I even implement my cache, I need to figure out how (and where) to properly make my request. Can anyone assist me with this?
Related
UPDATE at the bottom.
I have followed the UIKit section of this Apple iOS Dev Tutorial, up to and including the Saving New Reminders section. The tutorials provide full code for download at the beginning of each section.
But, I want to get FirebaseFirestore involved. I have some other Firestore projects that work, but I always thought that I was doing something not quite right, so I'm always looking for better examples to learn from.
This is how I found Peter Friese's 3-part YT series, "Build a To-Do list with Swift UI and Firebase". While I'm not using SwiftUI, I figured that the Firestore code should probably work with just a few changes, as he creates a Repository whose sole function is to interface between app and Firestore. No UI involved. So, following his example, I added a ReminderRepository.
It doesn't work, but I'm so close. The UITableView looks empty but I know that the records are being loaded.
Stepping through in the debugger, I see that the first time the numberOfRowsInSection is called, the data hasn't been loaded from the Firestore, so it returns 0. But, eventually the code does load the data. I can see each Reminder as it's being mapped and at the end, all documents are loaded into the reminderRepository.reminders property.
But I can't figure out how to get the loadData() to make the table reload later.
ReminderRepository.swift
class ReminderRepository {
let remindersCollection = Firestore.firestore()
.collection("reminders").order(by: "date")
var reminders = [Reminder]()
init() {
loadData()
}
func loadData() {
print ("loadData")
remindersCollection.addSnapshotListener { (querySnapshot, error) in
if let querySnapshot = querySnapshot {
self.reminders = querySnapshot.documents.compactMap { document in
do {
let reminder = try document.data(as: Reminder.self)
print ("loadData: ", reminder?.title ?? "Unknown")
return reminder
} catch {
print (error)
}
return nil
}
}
print ("loadData: ", self.reminders.count)
}
}
}
The only difference from the Apple code is that in the ListDataSource.swift file, I added:
var remindersRepository: ReminderRepository
override init() {
remindersRepository = ReminderRepository()
}
and all reminders references in that file have been changed to
remindersRepository.reminders.
Do I need to provide a callback for the init()? How? I'm still a little iffy on the matter.
UPDATE: Not a full credit solution, but getting closer.
I added two lines to ReminderListViewController.viewDidLoad() as well as the referenced function:
refreshControl = UIRefreshControl()
refreshControl?.addTarget(self, action: #selector(refreshTournaments(_:)), for: .valueChanged)
#objc
private func refreshTournaments(_ sender: Any) {
tableView.reloadData()
refreshControl?.endRefreshing()
}
Now, when staring at the initial blank table, I pull down from the top and it refreshes. Now, how can I make it do that automatically?
Firstly create some ReminderRepositoryDelegate protocol, that will handle communication between you Controller part (in your case ReminderListDataSource ) and your model part (in your case ReminderRepository ). Then load data by delegating controller after reminder is set. here are some steps:
creating delegate protocol.
protocol ReminderRepositoryDelegate: AnyObject {
func reloadYourData()
}
Conform ReminderListDataSource to delegate protocol:
class ReminderListDataSource: UITableViewDataSource, ReminderRepositoryDelegate {
func reloadYourData() {
self.tableView.reloadData()
}
}
Add delegate weak variable to ReminderRepository that will weakly hold your controller.
class ReminderRepository {
let remindersCollection = Firestore.firestore()
.collection("reminders").order(by: "date")
var reminders = [Reminder]()
weak var delegate: ReminderRepositoryDelegate?
init() {
loadData()
}
}
set ReminderListDataSource as a delegate when creating ReminderRepository
override init() {
remindersRepository = ReminderRepository()
remindersRepository.delegate = self
}
load data after reminder is set
func loadData() {
print ("loadData")
remindersCollection.addSnapshotListener { (querySnapshot, error) in
if let querySnapshot = querySnapshot {
self.reminders = querySnapshot.documents.compactMap { document in
do {
let reminder = try document.data(as: Reminder.self)
print ("loadData: ", reminder?.title ?? "Unknown")
delegate?.reloadYourData()
return reminder
} catch {
print (error)
}
return nil
}
}
print ("loadData: ", self.reminders.count)
}
}
Please try changing var reminders = [Reminder]() to
var reminders : [Reminder] = []{
didSet {
self.tableview.reloadData()
}
}
I have a tabBarController and in one of the tabs I can select whatever document to be in my Favourites tab.
So when I go to the Favourites tab, the favourite documents should appear.
I call the reloading after fetching from CoreData the favourite documents:
override func viewWillAppear(_ animated: Bool) {
languageSelected = UserDefaults().string(forKey: "language")!
self.title = "favourites".localized(lang: languageSelected)
// Sets the search Bar in the navigationBar.
let search = UISearchController(searchResultsController: nil)
search.searchResultsUpdater = self
search.obscuresBackgroundDuringPresentation = false
search.searchBar.placeholder = "searchDocuments".localized(lang: languageSelected)
navigationItem.searchController = search
navigationItem.hidesSearchBarWhenScrolling = false
// Request the documents and reload the tableView.
fetchDocuments()
self.tableView.reloadData()
}
The fetchDocuments() function is as follows:
func fetchDocuments() {
print("fetchDocuments")
// We make the request to the context to get the documents we want.
do {
documentArray = try context.fetchMOs(requestedEntity, sortBy: requestedSortBy, predicate: requestedPredicate)
***print(documentArray) // To test it works ok.***
// Arrange the documentArray per year using the variable documentArrayPerSection.
let formatter = DateFormatter()
formatter.dateFormat = "yyyy"
for yearSection in IndexSections.sharedInstance.allSections[0].sections {
let documentsFilteredPerYear = documentArray.filter { document -> Bool in
return yearSection == formatter.string(from: document.date!)
}
documentArrayPerSection.append(documentsFilteredPerYear)
}
} catch {
print("Error fetching data from context \(error)")
}
}
From the statement print(documentArray) I see that the function updates the content. However there is no reload of documents in the tableView.
If I close the app and open it again, then it updates.
Don't know what am I doing wrong!!!
The problem is that you're always appending to documentArrayPerSection but never clearing it so I imagine the array was always getting bigger but only the start of the array which the data source of the tableView was requesting was being used. Been there myself a few times.
I assume that reloadData() is called before all data processing is done. To fix this you will have to call completion handler when fetching is done and only then update tableView.
func fetchDocuments(_ completion: #escaping () -> Void) {
do {
// Execute all the usual fetching logic
...
completion()
}
catch { ... }
}
And call it like that:
fetchDocuments() {
self.tableView.reloadData()
}
Good luck :)
I am trying to make an API call in my Swift project. I just started implementing it and i am trying to return a Swift Dictionary from the call.
But I think i am doing something wrong with the completion handler!
I am not able to get the returning values out of my API call.
import UIKit
import WebKit
import SafariServices
import Foundation
var backendURLs = [String : String]()
class ViewController: UIViewController, WKNavigationDelegate, WKUIDelegate {
#IBOutlet var containerView : UIView! = nil
var webView: WKWebView!
override func viewDidLoad() {
super.viewDidLoad()
self.getBackendURLs { json in
backendURLs = self.extractJSON(JSON: json)
print(backendURLs)
}
print(backendURLs)
}
func getBackendURLs(completion: #escaping (NSArray) -> ()) {
let backend = URL(string: "http://example.com")
var json: NSArray!
let task = URLSession.shared.dataTask(with: backend! as URL) { data, response, error in
guard let data = data, error == nil else { return }
do {
json = try JSONSerialization.jsonObject(with: data, options: .mutableContainers) as? NSArray
completion(json)
} catch {
#if DEBUG
print("Backend API call failed")
#endif
}
}
task.resume()
}
func extractJSON(JSON : NSArray) -> [String : String] {
var URLs = [String : String]()
for i in (0...JSON.count-1) {
if let item = JSON[i] as? [String: String] {
URLs[item["Name"]! ] = item["URL"]!
}
}
return URLs
}
}
The first print() statements gives me the correct value, but the second is "nil".
Does anyone have a suggestion on what i am doing wrong?
Technically #lubilis has answered but I couldn't fit this inside a comment so please bear with me.
Here's your viewDidLoad
override func viewDidLoad() {
super.viewDidLoad()
self.getBackendURLs { json in
backendURLs = self.extractJSON(JSON: json)
print(backendURLs)
}
print(backendURLs)
}
What will happen is the following:
viewDidLoad is called, backendURLs is nil
you call getBackendURLs, which starts on another thread in the background somewhere.
immediately after that your code continues to the outer print(backendURLs), which prints nil as backendURLs is still nil because your callback has not been called yet as getBackendURLs is still working on another thread.
At some later point your getBackendURLs finishes retrieving data and parsing and executes this line completion(json)
now your callback is executed with the array and your inner print(backendURLs) is called...and backendURLs now has a value.
To solve your problem you need to refresh your data inside your callback method.
If it is a UITableView you could do a reloadData() call, or maybe write a method that handles updating the UI for you. The important part is that you update the UI inside your callback, because you don't have valid values until then.
Update
In your comments to this answer you say:
i need to access the variable backendURLs right after the completionHandler
To do that you could make a new method:
func performWhateverYouNeedToDoAfterCallbackHasCompleted() {
//Now you know that backendURLs has been updated and can work with them
print(backendURLs)
//do what you must
}
In the callback you then send to your self.getBackendURLs, you invoke that method, and if you want to be sure that it happens on the main thread you do as you have figured out already:
self.getBackendURLs { json in
backendURLs = self.extractJSON(JSON: json)
print(backendURLs)
DispatchQueue.main.async {
self.performWhateverYouNeedToDoAfterCallbackHasCompleted()
}
}
Now your method is called after the callback has completed.
As your getBackendURLs is an asynchronous method you can not know when it has completed and therefore you cannot expect values you get from getBackedURLs to be ready straight after calling getBackendURLs, they are not ready until getBackendURLs has actually finished and is ready to call its callback method.
Hope that makes sense.
I'm currently struggling to find an easy-to-use programming approach/design pattern, which solves the following problem:
I've got an REST API where the iOS app can request the required data. The data is needed in different ViewControllers. But the problem is, that the data should "always" be up to date. So I need to set up a timer which triggers a request every 5-20 seconds, or sth like that. Everytime the data changes, the view needs to be updated (at the current viewcontroller, which is displayed).
I tried some stuff with delegation and MVC Pattern, but it's kind a messy. How is it done the right way?
In my current implementation I only can update the whole UICollectionView, not some specific cells, because I don't know how the data changed. My controller keeps track of the data from the api and updates only if the hash has changed (if data changed on the server). My models always holds the last fetched data.
It's not the perfect solution, in my opinion..
I also thought about models, that keep themselves up to date, to abstract or virtualise my Rest-API. In this case, my controller doesn't even know, that it isn't directly accessible data.
Maybe someone can help me out with some kind of programming model, designpattern or anything else. I'm happy about anything!
UPDATE: current implementation
The Controller, which handles all the data
import Foundation
import SwiftyJSON
import SwiftyTimer
class OverviewController {
static let sharedInstance = OverviewController()
let interval = 5.seconds
var delegate : OverviewControllerUpdateable?
var model : OverviewModel?
var timer : NSTimer!
func startFetching() -> Void {
self.fetchData()
timer = NSTimer.new(every: interval) {
self.fetchData()
}
timer.start(modes: NSRunLoopCommonModes)
}
func stopFetching() -> Void {
timer.invalidate()
}
func getConnections() -> [Connection]? {
return model?.getConnections()
}
func getConnectionsSlave() -> [Connection]? {
return model?.getConnectionsSlave()
}
func getUser() -> User? {
return model?.getUser()
}
func countConnections() -> Int {
if let count = model?.getConnections().count {
return count
}
return 0
}
func countConnectionsSlave() -> Int {
if let count = model?.getConnectionsSlave().count {
return count
}
return 0
}
func fetchData() {
ApiCaller.doCall(OverviewRoute(), completionHandler: { (data, hash) in
if let actModel = self.model {
if (actModel.getHash() == hash) {
//no update required
return
}
}
var connections : [Connection] = []
var connectionsSlave : [Connection] = []
for (_,connection):(String, JSON) in data["connections"] {
let connectionObj = Connection(json: connection)
if (connectionObj.isMaster == true) {
connections.append(connectionObj)
} else {
connectionsSlave.append(connectionObj)
}
}
let user = User(json: data["user"])
//model needs update
let model = OverviewModel()
model.setUser(user)
model.setConnections(connections)
model.setConnectionsSlave(connectionsSlave)
model.setHash(hash)
self.model = model
//prevent unexpectedly found nil exception
if (self.delegate != nil) {
self.delegate!.reloadView()
}
}, errorHandler: { (errors) in
}) { (progress) in
}
}
}
protocol OverviewControllerUpdateable {
func reloadView()
}
The model, which holds the data:
class OverviewModel {
var user : User!
var connections : [Connection]!
var connectionsSlave : [Connection]!
var connectionRequests : [ConnectionRequest]!
var hash : String!
...
}
And in the ViewController, I use it like this:
class OverviewVC: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate, OverviewControllerUpdateable {
let controller = OverviewController.sharedInstance
override func viewDidLoad() {
super.viewDidLoad()
self.controller.delegate = self
self.controller.startFetching()
}
//INSIDE THE UICOLLECTIONVIEW DELEGATE METHODS
...
if let user : User = controller.getUser() {
cell.intervalTime = interval
cell.nameLabel.text = "Ihr Profil"
}
...
func reloadView() {
self.userCollectionView.reloadData()
}
}
You could use a Singleton object to fetch your data periodically, then post notifications (using NSNotificationCenter) when the data is updated. Each view controller dependent on the data would listen for these notifications, then reload UI based on the updated data.
I am new to IOS and swift. I am trying to implement an api get request that returns json and then display it in a table. Below is my current code. When I run simulator I am getting the following error:
fatal error: Cannot index empty buffer
If I remove the hardcoded return 3 in the tableView function and instead use doDatItems.count nothing renders in the table because I guess the array of doDatItems starts empty before the get request is made. It seems like a timing thing? How do I ensure the get request is made before the table loads?
import UIKit
class ViewController: UIViewController, UITableViewDelegate {
var doDatItems:[String] = []
#IBOutlet weak var doDatItem: UITextField!
#IBOutlet weak var yourDoDats: UILabel!
#IBAction func addDoDat(sender: AnyObject) {
doDatItems.append(doDatItem.text)
println(doDatItems)
}
override func viewDidLoad() {
super.viewDidLoad()
let urlPath = "http://localhost:3000/dodats"
let url: NSURL = NSURL(string: urlPath)!
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithURL(url, completionHandler: {data, response, error -> Void in
println("Task completed")
if((error) != nil) {
// If there is an error in the web request, print it to the console
println(error.localizedDescription)
}
var err: NSError?
var jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &err) as NSDictionary
if(err != nil) {
// If there is an error parsing JSON, print it to the console
println("JSON Error \(err!.localizedDescription)")
} else {
let dataArray = jsonResult["dodats"] as [String]
for item in dataArray {
self.doDatItems.append(item)
}
// println(self.doDatItems)
}
})
task.resume()
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 3
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell
{
let cell = UITableViewCell(style: UITableViewCellStyle.Default, reuseIdentifier: "Cell")
println(self.doDatItems)
cell.textLabel?.text = self.doDatItems[indexPath.row]
return cell
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
I found several problems -
You ViewController should conform to UITableViewDatasource (which is missing, not sure how it went that far)
Do not return 3 when self.doDatItems does not have any items. It will cause a crash. As long as the data loads let the table remain empty. return self.doDatItems.count
Once data is loaded and ready to display from self.doDatItems array, just call reloadData() method of your table view.
Before that, you should have a reference (or IBOutlet) of your tableView so that you can call reloadData() from anywhere.
You need to trigger a page refresh once the data has been received and parsed.
Something along the lines of
self.tableView.reloadData()
In this delegate method, which return number of rows,
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int
Don't use static number as 3. Get your Array Count & return the count in here.
After the json response comes, reload the tableView. In objective-c it's done by
[tableView reloadData];