How to implement spinning wheel during a backend job? - ios

Question

I have a need to implement a spinning wheel during a backend job. I have my backend-job in a separate class.
class ViewControllerA: UITableViewController {
// Code
var GetBackendRecordObj = GetBackendRecord(initparam:param);
// CODE TO START ANIMATION (SPINNING WHEEL)
self.view.addSubview(self.activityIndicator)
self.activityIndicator.bringSubview(toFront: self.view)
self.activityIndicator.startAnimating()
// CODE TO CALL THE BACKEND IS IN ANOTHER CLASS
GetBackendRecordObj.fetch_record()
}
class GetBackendRecord{
var transaction_id: String = ""
var current_email_id: String = ""
init(initparam: String) {
self.initparam = initparam
}
func fetch_record (){
do{
DispatchQueue.global(qos: .userInitiated).async {
//code
DispatchQueue.main.async { () -> Void in
//code to process response from backend
// NEED CODE TO STOP ANIMATION (SPINNING WHEEL)THAT WAS STARTED IN VIEWCONTROLLERA
})
}
}
}
How can I access the UITableViewcontroller after the backend call is done, so I can stop the animation. OR If there is a better way to start / stop animation when executing a backend-job (in a separate class) please let me know.

Answer 1

Add a completion handler to fetch_record:
func fetch_record(_ completionHandler: #escaping () -> Swift.Void) {
do{
DispatchQueue.global(qos: .userInitiated).async {
//code
DispatchQueue.main.async { () -> Void in
//code to process response from backend
completionHandler()
})
}
}
}
When calling it in your ViewController, you can specify what to do after completion:
GetBackendRecordObj.fetch_record() {
self.activityIndicator.stopAnimating()
}

Answer 2

If you need to know when the response returns so that you can stop the loader, you need to add a completion handler to the method that makes your internet call. You should generally have completion handlers on most methods that make internet calls, especially if you need UI things to happen only once you have gotten a response.
So for the fetchRecord function:
I have added a completion handler to this call. Preferably you would hand something off here just after #escaping(something like a dictionary or an array if it is a JSON response) and then process that response in another method. But if you want the code to process the response in this method with the threading that you've set up here, then I've written it accordingly.
func fetch_record(withCompletion comp: #escaping () ->()){
do{
DispatchQueue.global(qos: .userInitiated).async {
//code
DispatchQueue.main.async { () -> Void in
//code to process response from backend
//this tells whatever called this method that it is done
comp()
})
}
}
}
Then in your view controller when you call GetBackendRecordObj.fetch_record()
GetBackendRecordObj.fetch_record(withCompletion: { [weak self] () in
//when it hits this point, the process is done
self?.activityIndicator.stopAnimating()
}

Answer 3

Instead of activityIndicator better to use MBProgressHUD.
https://github.com/jdg/MBProgressHUD
To show MBProgressHUD
let loadingNotification = MBProgressHUD.showHUDAddedTo(self.view, animated: true)
loadingNotification.mode = MBProgressHUDMode.Indeterminate
loadingNotification.labelText = "Loading"
To hide MBProgressHUD
DispatchQueue.main.async { () -> Void in
MBProgressHUD.hideAllHUDsForView(self.view, animated: true)
})
You can implement show MBProgressHUD in seperate class from where you initiate back end job and hide code once your back end process finish.