can't set data to the variable when i parse json - ios

Question

I am currently trying to set data I get from parsing my json to a variable in my ViewController from RawDataCategory file, which decodes json.
Here is how I call a static method in CategoryViewController
class CategoryViewController: UIViewController {
#IBOutlet weak var tableView: UITableView!
var categoryProducts: [Datum]? // this is the variable i want with data i get
override func viewDidLoad() {
super.viewDidLoad()
tableView.dataSource = self
tableView.delegate = self
Datum.fetchProducts { (categoryProductsFromJSON) -> () in // here i call a static function.. i will paste the code below
self.categoryProducts = categoryProductsFromJSON //here i set value
print(self.categoryProducts?[0].name) // if i try to print the value in the scope i can access it. and it shows with no problem
}
print(categoryProducts?[0].name) //here is the problem. when i get out of the scope it return nil.
}
}
I can access the variable in the scope but somehow when i try to call it outside it prints nil.
Here is the static function (method) i call to get decoded json:
static func fetchProducts(_ completionHandler: #escaping ([Datum]) -> ()) {
guard let url = URL(string: "http://localhost:8888/dayhandan/public/api/v1/category/1") else { return }
let session = URLSession(configuration: .default)
let task = session.dataTask(with: url, completionHandler: { (data, response, error) -> Void in
if error != nil {
print("error")
return
}
do {
print("no error so far")
guard let data = data else { return }
let rawData = try JSONDecoder().decode(CategoryRawData.self, from: data)
DispatchQueue.main.async(execute: { () -> Void in
completionHandler(rawData.data ?? [])
})
} catch let err {
print(err)
}
})
task.resume()
}
I don't get any errors while i decode json. In fact I can pass it to my ViewContoller. There are no errors overall. categoryProducts just becomes nil when i call it outside the scope.
Is this a good way to use decoded data. if it is can someone help me to solve the issue. or can someone point at a good way to use decoded data. Thanks for your time

Answer 1

You should only try to use the result of fetchProducts in the completion handler because the completion handler will be executed at some point in the future. Anything outside of the completion handler will be executed immediately.
Reload your tableView from within the completion handler:
Datum.fetchProducts { (categoryProductsFromJSON) -> () in
self.categoryProducts = categoryProductsFromJSON
DispatchQueue.main.async {
self.tableView.reloadData()
}
}
Then you should have some logic to populate the tableView:
extension CategoryViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return categoryProducts?.count ?? 0
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
// something like this
guard let category = categoryProducts?[indexPath.row] else { return UITableViewCell() }
let cell = tableView.dequeueReusableCell(withIdentifier: "cell")
cell.titleLabel?.text = category.title
return cell
}
}