Swift - Troubles with API calls / CompletionHandler / URLSessions - ios

Question

I have this long function here which makes a bunch of API calls, parses through data and returns two arrays representing a bunch of sight-seeing locations (one array holds the latitudes, one holds the latitudes). The issue I am having is determining when the two arrays are finished being populated. Ideally, I would like to be able to place
print("ArrayCount = \(self.latArray.count)")
somewhere in my code and receive a single print statement in the console reading ArrayCount = 123. However everywhere I place the print statement I get either an array count of 0 or a loop of values being printed out as they are added (1..2..3.. ... ..123). Thanks in advance!
func someFunction()
{
let url:URL = URL(string: "...")
let task = URLSession.shared.dataTask(with: URLRequest(url: url))
{
data, response, error in
if error != nil
{
print("ERROR IN API REQUEST: \(error!.localizedDescription)")
}
else
{
do
{
if let parsedData = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String: Any]
{
if let layerOne = parsedData["one"] as? [String: Any]
{
if let layerTwo = layerOne["two"] as? [[String: Any]]
{
for layerThree in layerTwo
{
if let variableName = layerThree["value"] as? String
{
let innerUrl:URL = URL(string: "...")!
let innerTask = URLSession.shared.dataTask(with: URLRequest(url: innerUrl))
{
data, response, error in
if error != nil
{
print("ERROR IN API REQUEST: \(error!.localizedDescription)")
}
else
{
do
{
if let parsedData = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String: Any]
{
if let layerA = parsedData["A"] as? [String: Any]
{
if let lat = layerA["Latitude"] as? String, let long = layerA["Longitude"] as? String
{
self.latArray.append(lat)
self.longArray.append(lon)
}
}
}
}
catch
{
print("ERROR IN JSON SERIALIZATION")
}
}
}
innerTask.resume()
}
}
}
}
}
}
catch
{
print("ERROR IN JSON SERIALIZATION")
}
}
}
task.resume()
}

Answer 1

I'm not sure exactly what you're trying to do, but once I thinned out your incredibly verbose code and tried to understand it, I think the conclusion is that you'll only want to record the array counts after the last iteration of your inner loop. For example:
Instead of doing this: for layerThree in layerTwo
do this: for (index, layerThree) in layerTwo.enumerated()
Then, after you append the lat/long values, add this check:
if index == layerTwo.count - 1 //if this is our last inner loop
{
//print the array counts
print("Lat count: \(latArray.count)")
print("Long count: \(longArray.count)")
}
This should work in your case. However, I disagree entirely with the execution of this simply because of the lack of portability and reusability of your code. Additionally, there are quite a few good language constructs which are being ignored. The relentless nested if let blocks could be reduced significantly with a few good guard statements. Furthermore, considering you aren't handling your errors in any catch blocks anyway, might as well just remove them and opt for a try? instead. One much swiftier way of handling things would be to just include a completion handler in the function itself so that the array count printing logic could be handled elsewhere. I'll include some example code of how I would clean things up:
func someFunction(completion: (([String], [String]) -> Void)?)
{
let url = URL(string: "...")!
var latArray: [String] = []
var longArray: [String] = []
let task = URLSession.shared.dataTask(with: URLRequest(url: url),
completionHandler: { (data, response, error) -> Void in
guard error == nil else
{
print("ERROR IN API REQUEST: \(error?.localizedDescription)")
return
}
guard let parsedData = try? JSONSerialization.jsonObject(with: data!, options: .allowFragments),
let parsedDict = parsedData as? [String: Any],
let layerOne = parsedDict["one"] as? [String: Any],
let layerTwo = layerOne["two"] as? [[String: Any]] else
{
print("JSON OBJECT DOES NOT MATCH EXPECTED PATTERN")
return
}
for (index, layerThree) in layerTwo.enumerated()
{
guard let _ = layerThree["value"] as? String else
{
print("Skip this iteration (I guess?)")
continue
}
let innerUrl = URL(string: "...")!
let innerTask = URLSession.shared.dataTask(with: URLRequest(url: innerUrl),
completionHandler: { (data, response, error) -> Void in
guard error == nil else
{
print("ERROR IN API REQUEST: \(error?.localizedDescription)")
return
}
guard let parsedData = try? JSONSerialization.jsonObject(with: data!, options: .allowFragments),
let parsedDict = parsedData as? [String: Any],
let layerA = parsedDict["A"] as? [String: Any],
let lat = layerA["Latitude"] as? String,
let long = layerA["Longitude"] as? String else
{
print("Something went wrong")
return
}
latArray.append(lat)
longArray.append(long)
if index == layerTwo.count - 1 //if this is our last inner loop
{
completion?(latArray, longArray)
}
}
)
innerTask.resume()
}
}
)
task.resume()
}
someFunction(completion: { (latArray, longArray) -> Void in
//print the array counts
print("Lat count: \(latArray.count)")
print("Long count: \(longArray.count)")
})
This could still be improved much further, though based on your question I don't see that I personally should be putting more time into constructing this for you. It would be best if you come up with a few methods of your own to build an application with more readable and reusable code.