ios swift program flow - ios

Question

In my mainviewcontroller's viewDidLoad() method I am firing few processes.
let api = JsonData() // create instance of JsonData class
api.loadJson(nil) // this method receives json and writes it in the file.
//Function to find file location
func getFileURL(fileName: String) -> NSURL {
let manager = NSFileManager.defaultManager()
let dirURL = manager.URLForDirectory(.DocumentDirectory, inDomain: .UserDomainMask, appropriateForURL: nil, create: false, error: nil)
return dirURL!.URLByAppendingPathComponent(fileName)
}
//file with this name was created in loadJson method
let filePath = getFileURL("JSONFromServer.txt").path!
//trying to read this file
let newDictionary = NSKeyedUnarchiver.unarchiveObjectWithFile(filePath) as! [Dictionary <String,AnyObject> ]
I was expecting that file will be created in api.loadJson and straight after it I will be able to read it. But for some reason when I use debugger I see that there is no file yet. And only when program goes out from viewdidload method I can see that file was created.
I wonder if program flow is specific?
Here is my JsonData class:
import Foundation
class JsonData {
var bankDict = [Dictionary <String,AnyObject> ]()
var arrayOfBanks: [[String:AnyObject]] = []
func loadJson(completion: ((AnyObject) -> Void)!) {
var urlString = "http://almaz.com/getjson.php"
let session = NSURLSession.sharedSession()
let sourceUrl = NSURL(string: urlString)
var task = session.dataTaskWithURL(sourceUrl!){
(data, response, error) -> Void in
if error != nil {
println(error.localizedDescription)
} else {
var error: NSError?
var jsonData = NSJSONSerialization.JSONObjectWithData(data, options: .MutableContainers, error: &error) as! NSArray
//println(jsonData)
//convert from JSON into array of dictionaries
var rates = [ExchangeRates]() //instance of class Rate
var bnkDct = ["bank": "", "currency": "","buyrate": "", "sellrate": ""] //template
var indx : Int = 0 //index for iteration
for rate in jsonData{
let rate = ExchangeRates(rate as! NSDictionary)
rates.append(rate)
bnkDct["bank"] = rates[indx].bank
bnkDct["buyrate"] = rates[indx].buyRate
bnkDct["sellrate"] = rates[indx].sellRate
bnkDct["currency"] = rates[indx].currency
self.bankDict.append(bnkDct)
indx += 1
}
//println(self.bankDict)
//Store data in file
//File path and name
if let dirs : [String] = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.AllDomainsMask, true) as? [String] {
let dir = dirs[0] //documents directory
let filePath = dir.stringByAppendingPathComponent("JSONFromServer.txt");
NSKeyedArchiver.archiveRootObject(self.bankDict, toFile: filePath)
// println(filePath)
}
}
}
task.resume()
}
}

Answer 1

Your loadJson function takes a completion handler as a parameter but your loadJson function doesn't call it when it is done. Fix that first.
Then in your viewDidLoad function, pass in a completion handler when you call loadJson. The completion code you provide is where you should read and process the file saved by loadJson.