How to make async api calls in Swift - ios

Question

I am trying to make api call and print the result at UICollectionView cellForItemAt function but UICollectionView is lagging while fetching data from api. I tried collection view prefetching api but I couldn't implement it. How can I solve lagging scroll problem? Here is the problem:
Here is my api call class:
class ApiManager {
static var url: String?
static var header: [String : String]?
static var httpMethod: String?
static let session = URLSession.shared
static func getTask(itemName: String, completion:#escaping ([String]) -> Void) -> URLSessionDataTask {
let url = URL(string: ApiManager.url!)
var request = URLRequest(url: url!, cachePolicy: .useProtocolCachePolicy, timeoutInterval: 10.0)
request.allHTTPHeaderFields = ApiManager.header!
request.httpMethod = ApiManager.httpMethod
let session = ApiManager.session
let dataTask = session.dataTask(with: request) { data, response, error in
if error == nil && data != nil {
if (error != nil) {
print(error!)
} else {
do {
if let dictionary = try JSONSerialization.jsonObject(with: data!, options: []) as? [[String:Any]] {
var itemArray = [String]()
for index in 0...dictionary.count - 1 {
if let items = dictionary[index][itemName] as? String {
itemArray.append(items)
}
}
completion(itemArray)
}
} catch {
}
}
}
}
return dataTask
}
}
Here is my ViewController code:
class ViewController: UIViewController {
#IBOutlet weak var collectionView: UICollectionView!
var quoteArray = [String]()
var categories = ["love", "motivational", "mothersday", "all"]
override func viewDidLoad() {
super.viewDidLoad()
collectionView.delegate = self
collectionView.dataSource = self
for category in categories {
ApiManager.url = "https://famous-quotes4.p.rapidapi.com/random?category=\(category)&count=1000"
}
ApiManager.header = ["x-rapidapi-host": "famous-quotes4.p.rapidapi.com", "x-rapidapi-key": "SECRET_API_KEY" ]
ApiManager.httpMethod = "GET"
ApiManager.getTask(itemName: "text") { items in
DispatchQueue.main.async {
self.quoteArray.append(contentsOf: items)
self.collectionView.reloadData()
}
}.resume()
}
}
Here is my cellForItemAt func code:
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as? Cell else { fatalError("cell dequeue error") }
cell.label.text = self.quoteArray[indexPath.row]
return cell
}