Properly configuring closure to capture results - ios

Question

I am writing some custom store methods for in app purchases; sort of a wrapper for SwiftyStore. The problem I'm running into is the inability to get the results from the closures before they exit.
Any suggestions on how to properly set them up? IE: Closures...
I have a function that checks for an existing subscription and returns true if it finds one in firebase, if it doesn't then it goes out to the apple store to verify a previously purchased subscription:
func checkSubscription() -> Bool {
var RetVal: Bool = false
var retStat: String = ""
var myVal: Bool = false
self.rootRef.child("users").child(self.userID!).observeSingleEvent(of: .value, with: { (snapshot) in
// Get user value
let value = snapshot.value as? NSDictionary
let mySubType = value?["subtyp"] as? String ?? ""
// set value
if mySubType == "" {
// get receipt
if self.myStore.getReceipt() == true {
(myVal, retStat) = self.myStore.verifyPurchase(product: "com.xxxxx.xxxxx.monthly")
if myVal == true && retStat == "Valid" {
// we have a valid product update firebase
print("Valid")
} else if myVal == true && retStat == "Expired" {
// we have a valid product that is expired
print("Expired")
}
}
} else {
// we have a purchase, verify its not expired.
print("Purchased")
RetVal = true
}
}) { (error) in
print(error.localizedDescription)
}
return RetVal
}
The problem here is its dropping down to the return RetVal before the closure is complete so the function could be returning an invalid value. Not sure how I can fix this in the current setup, but any suggestions or pointers would be appreciated.

Answer 1

To expand on Tom's comment, if you want to return a result when the nested asynchronous function is complete, you could pass in a completion handler closure that uses the Result type that Swift offers like the following:
func checkSubscription(completion: #escaping (Result<Bool, Error>) -> Void) {
var RetVal: Bool = false
var retStat: String = ""
var myVal: Bool = false
self.rootRef.child("users").child(self.userID!).observeSingleEvent(of: .value, with: { (snapshot) in
// Get user value
let value = snapshot.value as? NSDictionary
let mySubType = value?["subtyp"] as? String ?? ""
// set value
if mySubType == "" {
// get receipt
if self.myStore.getReceipt() == true {
(myVal, retStat) = self.myStore.verifyPurchase(product: "com.xxxxx.xxxxx.monthly")
if myVal == true && retStat == "Valid" {
// we have a valid product update firebase
print("Valid")
} else if myVal == true && retStat == "Expired" {
// we have a valid product that is expired
print("Expired")
}
}
} else {
// we have a purchase, verify its not expired.
print("Purchased")
RetVal = true
}
completion(.success(RetVal))
}) { (error) in
print(error.localizedDescription)
completion(.failure(error))
}
}
Calling the function using this type of completion handler would look something like this:
checkSubscription { (result) in
switch result {
case .success(let boolValue):
// do something with resulting boolean
break
case .failure(let error):
// do something with resulting error
break
}
}

Answer 2

func checkSubscription(completion: (_ scuess:Bool) ->()){
var RetVal: Bool = false
var retStat: String = ""
var myVal: Bool = false
self.rootRef.child("users").child(self.userID!).observeSingleEvent(of: .value, with: { (snapshot) in
// Get user value
let value = snapshot.value as? NSDictionary
let mySubType = value?["subtyp"] as? String ?? ""
// set value
if mySubType == "" {
// get receipt
if self.myStore.getReceipt() == true {
(myVal, retStat) = self.myStore.verifyPurchase(product: "com.xxxxx.xxxxx.monthly")
if myVal == true && retStat == "Valid" {
// we have a valid product update firebase
print("Valid")
} else if myVal == true && retStat == "Expired" {
// we have a valid product that is expired
print("Expired")
}
}
completion(false)
} else {
// we have a purchase, verify its not expired.
print("Purchased")
completion(true)
}
}) { (error) in
print(error.localizedDescription)
completion(false)
}
return RetVal
}
call completion(true) whenever your retValue supposed to be true and completion(false) whenever your retValue supposed to be true
Then call this function this way:
checkSubscription { (sucuess) in
if(sucuess){
print("OK")
}else{
print("BAD")
}
}