Swift tableView slow and scroll lag - ios

Question

I am Pulling data from a json API Call the table view populates but is very slow and lags when scrolling down how do i speed up the loading of the table. I am new to swift and xcode any tips would be appreciates
import Foundation
import UIKit
class featuredViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
#IBOutlet weak var tableView: UITableView!
#IBOutlet weak var searchBar: UISearchBar!
// Array for JSON Data
var property: [featuredClass.property] = []
var imageArray = [String]()
var imageCollection = [[String]]()
var refreshControl: UIRefreshControl!
override func viewDidLoad() {
super.viewDidLoad()
self.getProperties()
// Do any additional setup after loading the view, typically from a nib.
refreshControl = UIRefreshControl()
refreshControl.attributedTitle = NSAttributedString(string: "Pull to refresh")
refreshControl.addTarget(self, action: #selector(featuredViewController.getProperties), for: UIControlEvents.valueChanged)
tableView.addSubview(refreshControl)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
/***********************************************************************************************/
func getProperties() {
let downloadTask = APICalls.getFeatured()
URLSession.shared.dataTask(with: downloadTask, completionHandler: {(data, response, error) -> Void in
if let httpResponse = response as? HTTPURLResponse {
print("statusCode: \(httpResponse.statusCode)")
}
/******** Parse JSON **********/
do { // A Dictionary of Dictionaries
let jsonObject = try JSONSerialization.jsonObject(with: data!, options: JSONSerialization.ReadingOptions.mutableContainers)
if let jsonDict = jsonObject as? NSDictionary {
// Do smthg.
//print(jsonDict) // Debug the json
let meCount = Int((jsonDict.count)) - 1; //get number to use for our loop
for index in 0...meCount {
for (_, value) in jsonDict { //Turns every key's value into a dictionary
// Fill property struct from json
self.property.append(featuredClass.property.init(jsonDict: value as! NSDictionary))
//print(self.property) // Uncomment for debugging
/** Get Image 0 for featured Image **/
let myData = self.property[index].image
// print(myData ?? "Error")
if myData?["0"] != nil {
let myData2 = myData?["0"] as! NSDictionary
self.imageArray.append(myData2["url"] as! String)
//print(myData2["url"] as! String)
}
else {
self.imageArray.append("\(#imageLiteral(resourceName: "property-placeholder-800x500"))")
}
/* ENd Get image 0 */
}
}
}
}catch {
//...
}
let meCount = (self.property.count)-1
/******** End Parse JSON **********/
//print(meCount)
if meCount != -1 {
}
else {
// Show alert view
let contactAddedAlert = UIAlertController(title: "Error: Check if Access Key is correct",
message: nil, preferredStyle: .alert)
contactAddedAlert.addAction(UIAlertAction(title: "OK", style: .cancel, handler: nil))
self.present(contactAddedAlert, animated: true, completion: nil)
}
/******** Reload table View **********/
OperationQueue.main.addOperation({
self.tableView.reloadData()
self.refreshControl.endRefreshing()
}) }).resume()
}
/***********************************************************************************************/
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return property.count
}
/***********************************************************************************************/
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cellFeatured") as! featuredTableViewCell
cell.addressLabel.text = property[indexPath.row].address
cell.cityNameLabel.text = property[indexPath.row].cityName
let imgURL = NSURL(string: imageArray[indexPath.row])
if imgURL != nil {
let data = NSData(contentsOf: (imgURL as URL?)!)
cell.imgView.image = UIImage(data: data! as Data)
}
return cell
}
}

Answer 1

NSData(contentsOf: (imgURL as URL?)!) is synchronous. Please refer to the SDK document: https://developer.apple.com/reference/foundation/nsdata/1547245-datawithcontentsofurl
Which state that:
Do not use this synchronous method to request network-based URLs. For network-based URLs, this method can block the current thread for tens of seconds on a slow network, resulting in a poor user experience, and in iOS, may cause your app to be terminated.
Instead, for non-file URLs, consider using the dataTaskWithURL:completionHandler: method of the NSURLSession class. See URL Session Programming Guide for details.

Answer 2

You can use this pod to boost your speed
https://github.com/rs/SDWebImage
It will be great to load images.