Using completion handlers inside while loop - swift

Question

How to use completion handlers/dispatchqueue within while loops?
I have this method called getHub() which is a completion handler as I would like code to be executed after it has finished with the relevant values. I call this when a user presses a button:
SetupAPI().getHub(completion: { response, error in
print("testing")
print(response)
print(error)
})
(The code above is where all of the code below should end at)
It calls my API and if the API returns an error/a value that I wasn't expecting, or if Almofire couldn't do the request for some reason, then it adds one onto the tries variable. The max amount of tries allowed is 3 given by the maxTries variable. If the tries variable is equal to the maxTries variable, then a bool timeout is set to true. If the tries variable is below the maxTries variable then the code waits timeoutInSeconds - which is 10 seconds - amount of time before exiting the while loop, which should run the code once more.
Similarly, If the right value is returned from fetching the data from my API then a bool found is set to true.
If either of these variables are true, then the while loop breaks. And an error is sent back to the completion handler for the code above (which then allows me to tell the user that something has gone wrong).
However, when I run it, the completion handler above is not finished, and the code just runs through the while loop and called function over and over again as my console fills with starting and fetching via my two print statements for debugging in below code. What's the problem, can I use a DispatchQueue/ completion handlers in this situation?
Function that gets called via above code:
func getHub(completion: #escaping (Bool, Error?) -> Void) {
var tries = 0
let maxTries = 3
let timeoutInSeconds = 10.0
var found = false
var timeout = false
while !found || !timeout{
print("starting")
getHubCallAPI(completion: {status, error in
if(error == nil){
print(status)
if (status == "No documents found"){
if(tries >= maxTries){
print("Tired too many times")
timeout = true
return completion(false, nil)
}
tries += 1
DispatchQueue.main.asyncAfter(deadline: .now() + timeoutInSeconds){
return
}
}else{
found = true
print("Hub found")
return completion(true, nil)
}
}else{
print("error")
return completion(false, error)
}
})
}
}
Function that calls the API and returns it back to the function above ^^:
func getHubCallAPI(completion: #escaping (String, Error?) -> Void) {
print("fetching")
AF.request("https://discovery.ellisn.com", encoding: URLEncoding.default).response { response in
print("Request: \(response.request)")
print("Response: \(response.response)")
print("Error: \(response.error)")
if(response.error != nil){
return completion("", response.error)
}
if let data = response.data, let status = String(data: data, encoding: .utf8) {
return completion(status, nil)
}
}
}
Any questions, or more clarification needed, then just ask. Thanks.

Answer 1

You can try the following:
func getHub(triesLeft: Int = 3, completion: #escaping (Bool, Error?) -> Void) {
let timeoutInSeconds = 1.0
print("starting")
getHubCallAPI(completion: { status, error in
if error == nil {
print(status)
if status != "No documents found" {
print("Hub found")
return completion(true, nil)
}
} else {
print("error")
return completion(false, error) // comment out if the loop should continue on error
}
if triesLeft <= 1 {
print("Tried too many times")
return completion(false, nil)
}
DispatchQueue.main.asyncAfter(deadline: .now() + timeoutInSeconds) {
getHub(triesLeft: triesLeft - 1, completion: completion)
}
})
}
And just call it once like this:
getHub(triesLeft: 2, completion: { ... })
Note that unless you need it for some other reason, there is no need to return (Bool, Error?). And the second parameter is always nil - you may want to propagate your error. You could in theory return (String?, Error?).