series of cloudkit callbacks - when to popover to previous controller - swift

Question

I have series of sequential cloud kit calls to fetch records each based on previous fetch. Any one of these fetches may fail and then I have to popover to previous controller. Since there are so many places the fetches can fail, I have to embed popViewController to previous controller in many locations. Can I avoid this and call popover only once if it is possible?
func iCloudSaveMeterHubPrivateDbCz() {
self.clOps.iCloudFetchRecord(recordName: locId, databaseScope: CKDatabaseScope.private, customZone: true, completion: { (locationRecord, error) in
guard error == nil else {
self.navigationController!.popViewController(animated: true)
return
}
self.iCloudFetchMeter(withLocationCKRecord: locationRecord!) { records, error in
if (error != nil ) {
if let ckerror = error as? CKError {
self.aErrorHandler.handleCkError(ckerror: ckerror)
}
self.navigationController!.popViewController(animated: true)
}
if let _ = records?.first {
self.clOps.iCloudFetchRecord(recordName: contactId, databaseScope: CKDatabaseScope.private, customZone: true, completion: { (contactRecord, error) in
if let ckerror = error as? CKError {
self.aErrorHandler.handleCkError(ckerror: ckerror)
self.navigationController!.popViewController(animated: true)
}
DispatchQueue.main.async {
if let record = contactRecord {
record.setObject("true" as NSString, forKey:"assignedEEP")
}
}
}
self.navigationController!.popViewController(animated: true)
}
}
})
}

Answer 1

Whenever I get into nested callbacks like this, I try to consolidate handling a response to a single point in the code. The popular motto of coders helps in this case: "don't repeat yourself"
Here's a suggestion for consolidating error handling and popping to a single place by making your main function have a closure:
func iCloudSaveMeter(finished: #escaping (_ success: Bool, _ error: CKError?) -> Void){
self.clOps.iCloudFetchRecord(recordName: locId, databaseScope: CKDatabaseScope.private, customZone: true, completion: { (locationRecord, error) in
if error != nil {
//:::
finished(false, error)
}
self.iCloudFetchMeter(withLocationCKRecord: locationRecord!) { records, error in
if error != nil {
//:::
finished(false, error)
}
if let _ = records?.first {
self.clOps.iCloudFetchRecord(recordName: contactId, databaseScope: CKDatabaseScope.private, customZone: true, completion: { contactRecord, error in
//:::
finished(false, error)
DispatchQueue.main.async {
if let record = contactRecord {
record.setObject("true" as NSString, forKey:"assignedEEP")
}
}
}
}
//:::
finished(true, nil)
}
})
}
//----
//Call it like this
iCloudSaveMeter(){ success, error in
//Pop
if !success{
self.navigationController!.popViewController(animated: true)
}
//Hande error
if let error = error{
self.aErrorHandler.handleCkError(ckerror: error)
}
}