Swift - Stop TableView Reloading After Dismissing A ViewController - ios

Question

I have a tableview that populates after a fetch request completes. Each row contains a link that opens in a SFSafariViewController. Once the user taps the Done button in the SF Safari VC, the tableview reloads and calls the fetch request again. I don't want this to happen as the fetch request can sometimes take upwards of 15 sec and I'm afraid its doubling my API call count.
Code below - is there anything I can do to prevent the tableview reloading once the Safari VC is dismissed? I tried using a boolean to track it but it simply gets changed again when viewDidLoad /appear gets called. Should I call my fetch request outside of viewdidload/appear somehow?
import SafariServices
import UIKit
class ArticlesTVC: UITableViewController, SFSafariViewControllerDelegate {
var articles = [Article]()
let cellId = "articleCell"
var refresh: Bool = false
override func viewDidLoad() {
super.viewDidLoad()
registerCell()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(true)
refresh = true
if refresh == true {
DispatchQueue.main.async {
self.fetchArticles()
self.refresh = false
}
}
}
func registerCell() { tableView.register(UITableViewCell.self, forCellReuseIdentifier: cellId) }
override func numberOfSections(in tableView: UITableView) -> Int { return 1 }
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int { return articles.count }
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath)
let article = articles[indexPath.row]
cell.textLabel?.text = article.title
cell.detailTextLabel?.text = article.description
return cell
}
override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
let article = articles[indexPath.row]
loadArticle(articleURL: article.url!)
}
func loadArticle(articleURL: String) {
if let url = URL(string: articleURL) {
let vc = SFSafariViewController(url: url)
vc.delegate = self
present(vc, animated: true)
}
}
func safariViewControllerDidFinish(_ controller: SFSafariViewController) {
dismiss(animated: true)
}
func fetchArticles() {
let baseURL = "url removed for privacy"
guard let url = URL(string: "\(baseURL)") else {
print("url failed")
return
}
let session = URLSession(configuration: .default)
let task = session.dataTask(with: url) { data, response, error in
if error != nil {
print(error)
return
}
if let safeData = data {
self.parseJSON(data: safeData)
}
}.resume()
}
func parseJSON(data: Data) {
let decoder = JSONDecoder()
do {
let decodedData = try decoder.decode(ArticleEnvelope.self, from: data)
let newsArticles = decodedData.news
for item in newsArticles {
let title = item.title
let description = item.description
let url = item.url
let image = item.image
let published = item.published
let article = Article(title: title, description: description, url: url, image: image, published: published)
DispatchQueue.main.async {
self.articles.append(article)
self.tableView.reloadData()
}
}
print("articles loaded successfully")
} catch {
print("Error decoding: \(error)")
}
}

Answer 1

Of course. You are 90% of the way there. Your viewWillAppear(_:) method checks a boolean flag refresh, and only fetches the data and reloads the table if refresh == true. However, it explicitly sets refresh = true. Your viewWillAppear(_:) function gets called every time you dismiss your other view controller and re-display the table view controller.
Move the line refresh = true into viewDidLoad(). Problem solved. (viewDidLoad() is only called once when the view controller is first created, not each time it is uncovered by dismissing/popping a view controller that is covering it.)
Edit:
Note that in this code:
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(true)
refresh = true
if refresh == true {
DispatchQueue.main.async { //This bit is not needed
self.fetchArticles()
self.refresh = false
}
}
}
The call to DispatchQueue.main.async is not needed, and will make fetching data slightly slower. viewWillAppear(_:) is already always called on the main thread.
Rewrite it like this:
override func viewDidLoad() {
super.viewDidLoad()
registerCell()
refresh = true //Moved from viewWillAppear
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(true)
//Remove refresh = true from this function.
if refresh == true {
//No need to use DispatchQueue.main.async here
self.fetchArticles()
self.refresh = false
}
}