parsing a JSON array in Swift - json

Question

I have this working but it seems like a very manual process and I can't work out how to loop inside a loop (or if I should). Right now I am just testing this with 3 variables, but there will ultimately be about 100. Here's my playground. Is there a way to simplify this so I don't have to manually add each array name?
import Foundation
var json_data_url = "216.92.214.107/data_test.json"
var LRKSFOweekdayDep : [String] = [String]()
var LRKSFOweekendDep : [String] = [String]()
var SFOLRKweekdayDep : [String] = [String]()
let journeysURL:NSURL = NSURL(string: json_data_url)!
let data = NSData(contentsOfURL: journeysURL)!
do {
let json = try NSJSONSerialization.JSONObjectWithData(data, options: .AllowFragments)
print(json)
if let dep_obj = json as? NSDictionary {
if let array_journey = dep_obj["journey"] as? NSArray{
if let journies = array_journey[0] as? NSDictionary {
if let array_dep = journies["LRKSFOweekdayDep"] as? NSDictionary{
if let dep = array_dep["dep"] as? NSArray {
for var i = 0; i < dep.count; ++i
{
let add = dep[i] as! String
LRKSFOweekdayDep.append(add)
}
print(LRKSFOweekdayDep)
}
}
}
if let journies = array_journey[1] as? NSDictionary {
if let array_dep = journies["LRKSFOweekendDep"] as? NSDictionary{
if let dep = array_dep["dep"] as? NSArray {
for var i = 0; i < dep.count; ++i
{
let add = dep[i] as! String
LRKSFOweekendDep.append(add)
}
print(LRKSFOweekendDep)
}
}
}
if let journies = array_journey[2] as? NSDictionary {
if let array_dep = journies["SFOLRKweekdayDep"] as? NSDictionary{
if let dep = array_dep["dep"] as? NSArray {
for var i = 0; i < dep.count; ++i
{
let add = dep[i] as! String
SFOLRKweekdayDep.append(add)
}
print(SFOLRKweekdayDep)
}
}
}
}
}
} catch {
print("error serializing JSON: \(error)")
}

Answer 1

You might want to look at using SwiftyJSON to make the parsing easier.

Answer 2

Right now, you have something like:
if let dep = array_dep["dep"] as? NSArray {
for var i = 0; i < dep.count; ++i {
let add = dep[i] as! String
LRKSFOweekendDep.append(add)
}
}
That can be simplified to:
LRKSFOweekendDep = array_dep["dep"] as? [String]
That assumes of course, that you define LRKSFOweekendDep to be optional. If it's not optional, you can do:
LRKSFOweekendDep = array_dep["dep"] as? [String] ?? []
But, it should be optional.
In a comment, you say that there are going to be 100 of these. Rather than having a variable for each, I would have thought that you'd rather keep an array of objects. For example, consider:
struct Journey {
let name: String
let departures: [String]
}
Then, to parse your JSON, you could iterate through the results:
let json = try NSJSONSerialization.JSONObjectWithData(data!, options: [])
var journeys = [Journey]()
if let results = json as? [String: AnyObject], let array = results["journey"] as? [[String: AnyObject]] {
for dictionary in array {
for (name, departures) in dictionary {
if let departureDictionary = departures as? [String: [AnyObject]], let departureList = departureDictionary["dep"] as? [String] {
journeys.append(Journey(name: name, departures: departureList))
}
}
}
}
Finally, I would advise against NSData(contentsOfURL:), because that's synchronous. Use NSURLSession's dataTaskWithURL, which is asynchronous. Also, if you use data! pattern, first check to make sure it's not nil. Otherwise, if data was nil for any reason outside of your control (e.g. the web server is down, internet is temporarily interrupted, etc.), the app will crash rather than handling it gracefully.
Putting that all together, you get something like:
func retrieveJourneys(completionHandler: ([Journey]?, NSError?) -> ()) {
let task = NSURLSession.sharedSession().dataTaskWithURL(journeysURL) { data, response, error in
guard error == nil && data != nil else {
completionHandler(nil, error)
return
}
var json: [String: AnyObject]?
do {
json = try NSJSONSerialization.JSONObjectWithData(data!, options: []) as? [String: AnyObject]
} catch let parseError as NSError {
completionHandler(nil, parseError)
}
var journeys = [Journey]()
if let array = json!["journey"] as? [[String: AnyObject]] {
for dictionary in array {
for (name, departures) in dictionary {
if let departureDictionary = departures as? [String: [AnyObject]], let departureList = departureDictionary["dep"] as? [String] {
journeys.append(Journey(name: name, departures: departureList))
}
}
}
}
completionHandler(journeys, nil)
}
task.resume()
}
And then you'd use it like so:
var journeys: [Journey]?
override func viewDidLoad() {
super.viewDidLoad()
retrieveJourneys { journeys, error in
guard error == nil && journeys != nil else { // make sure it didn't have network problem
print(error)
return
}
dispatch_async(dispatch_get_main_queue()) { // now update model on main queue
self.journeys = journeys
// and, for giggles and grins, this is how you might grab the first one and examine it:
let someJourney = self.journeys![0]
print(someJourney.name)
print(someJourney.departures)
}
}
}
Now, the above assumes that you wanted an ordered list of journeys, sorted by the order you received them.
On the other hand, if you didn't care about the order, but wanted an efficient way to retrieve the departures associated with a given key, you might use a dictionary, instead:
func retrieveDepartures(completionHandler: ([String: [String]]?, NSError?) -> ()) {
let task = NSURLSession.sharedSession().dataTaskWithURL(journeysURL) { data, response, error in
guard error == nil && data != nil else {
completionHandler(nil, error)
return
}
var json: [String: AnyObject]?
do {
json = try NSJSONSerialization.JSONObjectWithData(data!, options: []) as? [String: AnyObject]
} catch let parseError as NSError {
completionHandler(nil, parseError)
}
var departures = [String: [String]]()
if let array = json!["journey"] as? [[String: AnyObject]] {
for dictionary in array {
for (name, departureObject) in dictionary {
if let departureDictionary = departureObject as? [String: [AnyObject]], let departureList = departureDictionary["dep"] as? [String] {
departures[name] = departureList
}
}
}
}
completionHandler(departures, nil)
}
task.resume()
}
And then:
var departures: [String: [String]]?
override func viewDidLoad() {
super.viewDidLoad()
retrieveDepartures { departures, error in
guard error == nil && departures != nil else {
print(error)
return
}
dispatch_async(dispatch_get_main_queue()) {
self.departures = departures
// and, for giggles and grins, this is how you might grab a list of departures given a particular key
let departureTimes = self.departures!["LRKSFOweekdayDep"]
print(departureTimes)
}
}
}