reloadData on CollectionView, Swift - swift

Question

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! UsersCollectionViewCell
someRequest(username: self.usernameUrl) { (userInfo, error) in
guard let userInfo = userInfo else {
// present error
return
}
print("Running")
let user_image_url = userInfo.items.map{($0.avatarURL)}
cell.userCellLabel.text = user_name[indexPath.item]
}
return cell
}
Why the code inside someRequest( ... ) is not running when I call reloadData on viewDidAppear?
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
self.collectionViewUsers.reloadData()
}
P.s. Somerequest just perform an Alamofire get

Answer 1

Async Alamofire request must be outside of the cellForItemAt handler. Because cellForItemAt is called every time the cell appeared on the screen, that means it will try to fetch same data for same cell for multiple times while scrolling, which is not intended. So viewDidLoad is a good place to start fetching, after async call completed don't forget to reload collectionview.
var user_image_url: String?
override func viewDidLoad(_ animated: Bool) {
someRequest(username: self.usernameUrl) { (userInfo, error) in
guard let userInfo = userInfo else {
// present error
return
}
print("Running")
user_image_url = userInfo.items.map{($0.avatarURL)}
self.collectionViewUsers.reloadData()
}
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! UsersCollectionViewCell
if let user_image_url = user_image_url {
//user_image_url is avaliable
}
return cell
}