Can't get data from rest API to load on ViewDidLoad - json

Question

I'm new to swift and I can't get my head around this issue.
I can successfully make JSON fetch from an API, but data on the Table View only load after I click a button. Calling the same function on the viewDidLoad didn't load the data when the app is opening.
I tried lot of solutions, but I can't find where the fault is
here's the main view controller code:
import UIKit
struct ExpenseItem: Decodable {
let name: String
let amount: String
let id: String
let timestamp: String
let description: String
}
class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
#IBAction func fetchData(_ sender: Any) {
ds()
self.eTW.reloadData()
}
#IBOutlet weak var eTW: UITableView!
var allExpenses = [ExpenseItem]()
let expensesURL = "https://temp.cuttons.com/json/expenses.json"
override func viewDidLoad() {
super.viewDidLoad()
eTW.delegate = self
eTW.dataSource = self
ds()
self.eTW.reloadData()
}
func parseJSON(data: Data) -> [ExpenseItem] {
var e = [ExpenseItem]()
let decoder = JSONDecoder()
do {
e = try decoder.decode([ExpenseItem].self, from: data)
} catch {
print(error.localizedDescription)
}
return e
}
func ds() {
if let url = URL(string: expensesURL){
let session = URLSession(configuration: .default)
let task = session.dataTask(with: url) { (data, session, error) in
if error != nil {
print("some error happened")
} else {
if let content = data {
self.allExpenses = self.parseJSON(data: content)
}
}
}
task.resume()
}
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return self.allExpenses.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = eTW.dequeueReusableCell(withIdentifier: "expense", for: indexPath) as! myCellTableViewCell
cell.name.text = self.allExpenses[indexPath.row].name
if let am = Double(self.allExpenses[indexPath.row].amount) {
if (am > 0) {
cell.amount.textColor = .green
} else {
cell.amount.textColor = .red
}
}
cell.amount.text = self.allExpenses[indexPath.row].amount
return cell
}
thanks
L.

Answer 1

You have to reload the table view after receiving the data asynchronously.
Remove the line in viewDidLoad
override func viewDidLoad() {
super.viewDidLoad()
eTW.delegate = self
eTW.dataSource = self
ds()
}
and add it in ds
func ds() {
if let url = URL(string: expensesURL) {
let session = URLSession(configuration: .default)
let task = session.dataTask(with: url) { (data, response, error) in
if let error = error {
print("some error happened", error)
} else {
self.allExpenses = self.parseJSON(data: data!)
DispatchQueue.main.async {
self.eTW.reloadData()
}
}
}
task.resume()
}
}

Answer 2

Do not reload data after the api call in viewDidLoad(). Do it inside of the completion block after you parse the JSON into the object you need (assuming it's successful like you said).
let session = URLSession(configuration: .default)
let task = session.dataTask(with: url) { (data, session, error) in
guard error == nil else {
print("some error happened")
return
}
guard let data = data else {
print("bad JSON")
return
}
self.allExpenses = self.parseJSON(data: data)
DispatchQueue.main.async {
self.eTW.reloadData()
}
}
task.resume()
Also, use guard let instead of if let if possible.