Swift - Why fetching data from JSON have a blank TableView delay before data get displayed? - json

Question

Edit: Please ignore the old answers. I can't create a new question my accunt was blocked. So I edited this one with a new question in the title.
How can i have my data result as soon as i viewDidLoad my tableView ?
Here is a snippet of my code. Can anyone help me to understand the asynchronous part that make my code fetch data and bring me back the result late.
`
let apiUrl = "https://shopicruit.myshopify.com/admin/products.json?
page=1&access_token=c32313df0d0ef512ca64d5b336a0d7c6"
var myRowProduct : String = ""
var productArrayName : [String] = []
var productsPassedOver : [String] = []
override func viewDidLoad() {
super.viewDidLoad()
getFullProductsJson(url: apiUrl, tag1: myRowProduct){array, err in
if err != nil {
print("ERROR 2")
}else{
self.productsPassedOver = array
self.tableView.reloadData()
print("productsPassedOver \(self.productsPassedOver)")
}
}
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return productsPassedOver.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "ProductCell", for: indexPath)
cell.selectionStyle = .none
cell.textLabel?.text = "\(indexPath.row + 1). " + productsPassedOver[indexPath.row] + "\n" //label are in every single cell. The current text that is displayed by the label
cell.textLabel?.numberOfLines = 0; //removes any limitations on the number of lines displayed
return cell
}
//Networking JSON
func getFullProductsJson(url: String, tag1: String, completion: #escaping ([String], Error?) -> ()) {
Alamofire.request(url, method: .get).responseJSON {
response in
//response.result.value comes back as an optional so use ! to use it. Also value have datatype of Any? thats why we JSON casting
if response.result.isSuccess{
let fullJSON : JSON = JSON(response.result.value!)
let finalArrayOfProductS = self.updateTagProductData(json: fullJSON, tag2: tag1)
completion(finalArrayOfProductS, nil)
}
else{
print("Error JSON")
}
}
}
//JSON parsing, deal with formatting here
func updateTagProductData(json : JSON, tag2: String) -> [String]{
let tagClicked = tag2
var nbOfProducts : Int = 0
nbOfProducts = json["products"].count
var inventoryAvailableTotal : Int = 0
var nbOfVariants : Int = 0
for i in 0..<nbOfProducts {
let tagsGroup : String = json["products"][i]["tags"].stringValue
let productName : String = json["products"][i]["product_type"].stringValue
nbOfVariants = json["products"][i]["variants"].count
if tagsGroup.contains(tagClicked){
for j in 0..<nbOfVariants{
inventoryAvailableTotal += json["products"][i]["variants"][j]["inventory_quantity"].int!
}
print("\(tagClicked) tag exist in the product \(i): \(productName)")
print("inventorytotal \(inventoryAvailableTotal)")
productArrayName.append("\(productName): \(inventoryAvailableTotal) available")
}
}
return productArrayName
}
}
`

Answer 1

This is a function that does something in the background and return immediately, and when it finishes, it calls your completion handler.
So it is natural for this function to go directly to the return finaleNbOfRowsInProductsListPage.
Your solution is that the function shouldn't return the value, but it should
accept a completion handler, and call it when ended. This is the continuation passing style.
func getFullProductsJson(url: String, tag1: String, completion: #escaping (Int?, Error?) -> ()) {
Alamofire.request(url, method: .get).responseJSON {
response in
...
// When you are done
completion(finaleNbOfRowsInProductsListPage, nil)
}
}
Also please note to try avoiding setting a lot of variables, try to make everything a parameter or a return value from a function, this is easier to debug. For example, try to make the list as a parameter that is passed to the completion handler, not as a member variable of your view controller, make this member variable only for the list that is ready to be displayed.
func getFullProductsJson(url: String, tag1: String, completion: #escaping (Products?, Error?) -> ()) {
Alamofire.request(url, method: .get).responseJSON {
response in
...
// When you are done
completion(products, nil)
}
}
var products: [Product] = []
func refreshData() {
getFullProductsJson(url: "YOUR_URL_HERE", tag1: "TAG") {
// Try to use [weak self], also, read about Automatic Reference Counting
productsNullable, error in
if let products = productsNullable {
// Alamofire calls your callback on a background thread
// So you must return to the main thread first when you want
// to pass the result to any UI component.
DispatchQueue.main.async {
self?.products = products
self?.tableView.reloadData()
}
}
}
}