UITableView pagination, willDisplay loading infinitely - ios

Question

I'm trying to implement a chat feature in my app which will mimic iMessages' pull to load more messages. My API sends 20 messages in each call along with pageIndex and other values to keep track of pages and messages.
I'm implementing pagination using TableView willDisplay and pull to refresh features.
I'm not able to add correct logic to load more messages in willDisplay and it's going into infinite loop. Can anyone point me to right direction by looking at below code?
import UIKit
class ChatViewController: UIViewController, UITableViewDelegate, UITableViewDataSource, UITextViewDelegate {
#IBOutlet weak var messagesTable: UITableView!
#IBOutlet weak var activityIndicator: UIActivityIndicatorView!
var messages: Messages!
var messageArray = [Message]()
// Pagination
var isLoading = false
var pageSize = 10
var totalPages: Int!
var currentPage: Int!
// Pull To Refresh
let refreshControl = UIRefreshControl()
override func viewWillAppear(_ animated: Bool){
super.viewWillAppear(animated)
activityIndicator.startAnimating()
fetchMessages(page: 1, completed: {
self.totalPages = self.messages.pageCount
self.currentPage = self.messages.currentPage
// Sort message by ID so that latest message appear at the bottom.
self.messageArray = self.messages.messages!.sorted(by: {$0.id! < $1.id!})
self.messagesTable.reloadData()
// Scroll to the bottom of table
self.messagesTable.scrollToBottom(animated: false)
self.activityIndicator.stopAnimating()
})
}
// MARK: - Table view data source
func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return messageArray.count
}
func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
if !self.isLoading && indexPath.row == 0 {
self.isLoading = true
fetchMessages(page: self.currentPage, completed: {
if self.currentPage == 0 {
self.messageArray.removeAll()
}
self.messageArray.append(contentsOf: self.messages!.messages!)
self.messageArray = self.messageArray.sorted(by: {$0.id! < $1.id!})
self.messagesTable.reloadData()
// Scroll to the top
self.messagesTable.scrollToRow(at: indexPath, at: UITableViewScrollPosition.top, animated: true)
self.currentPage = self.currentPage + 1
})
self.isLoading = false
}
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
guard let cell = tableView.dequeueReusableCell(withIdentifier: "MessageCell", for: indexPath) as? MessageCell else {
fatalError("Can't find cell")
}
return cell
}
private func fetchMessages(page: Int, completed: #escaping () -> ()){
guard let url = URL(string: "http://example.com/....") else { return }
URLSession.shared.dataTask(with: url) { (data, response, error) in
if error != nil {
print("Error in fetching data..........")
print(error!.localizedDescription)
}
guard let data = data else { return }
if let str = String(data: data, encoding: .utf8) { print(str) }
do {
let resultData = try JSONDecoder().decode(messagesStruct.self, from: data)
DispatchQueue.main.async {
print("DispatchQueue.main.async")
self.messages = resultData.data!
completed()
}
} catch let jsonError {
print(jsonError)
}
}.resume()
}
//Pull to refresh
#objc func refresh(_ refreshControl: UIRefreshControl) {
fetchMessages(completed: {
self.messagesTable.reloadData()
})
refreshControl.endRefreshing()
}
}

Answer 1

willDisplayCell is not the safe place to check if tableView is actually scrolled to bottom rather use scrollViewDelegate
func scrollViewDidScroll(_ scrollView: UIScrollView) {
if !self.isLoading && (messagesTable.contentOffset.y >= (messagesTable.contentSize.height - messagesTable.frame.size.height)) {
self.isLoading = true
fetchMessages(page: self.currentPage, completed: {[weak self]
guard let strongSelf = self else {
return
}
strongSelf.isLoading = false
if strongSelf.currentPage == 0 {
strongSelf.messageArray.removeAll()
}
strongSelf.messageArray.append(contentsOf: strongSelf.messages!.messages!)
strongSelf.messageArray = strongSelf.messageArray.sorted(by: {$0.id! < $1.id!})
strongSelf.messagesTable.reloadData()
strongSelf.currentPage = strongSelf.currentPage + 1
})
}
}
Hope it helps