Swift JSON parsing with Dictionary with Array of Dictionaries - json

Question

I am a beginner in iOS development with Swift language. I have a JSON file contains the data as below.
{
"success": true,
"data": [
{
"type": 0,
"name": "Money Extension",
"bal": "72 $",
"Name": "LK_Mor",
"code": "LK_Mor",
"class": "0",
"withdraw": "300 $",
"initval": "1000 $"
},
{
},
{
},
]
}
I want to parse this file and have to return the dictionary which contain the data in the JSON file. This is the method I wrote.
enum JSONError: String, ErrorType {
case NoData = "ERROR: no data"
case ConversionFailed = "ERROR: conversion from JSON failed"
}
func jsonParserForDataUsage(urlForData:String)->NSDictionary{
var dicOfParsedData :NSDictionary!
print("json parser activated")
let urlPath = urlForData
let endpoint = NSURL(string: urlPath)
let request = NSMutableURLRequest(URL:endpoint!)
NSURLSession.sharedSession().dataTaskWithRequest(request) { (data, response, error) -> Void in
do {
guard let dat = data else {
throw JSONError.NoData
}
guard let dictionary: NSDictionary = try NSJSONSerialization.JSONObjectWithData(dat, options:.AllowFragments) as? NSDictionary else {
throw JSONError.ConversionFailed
}
print(dictionary)
dicOfParsedData = dictionary
} catch let error as JSONError {
print(error.rawValue)
} catch {
print(error)
}
}.resume()
return dicOfParsedData
}
When I modify this method to return a dictionary, it always return nil. How can I modify this method.

Answer 1

You can not return for an asynchronous task. You have to use a callback instead.
Add a callback like this one:
completion: (dictionary: NSDictionary) -> Void
to your parser method signature:
func jsonParserForDataUsage(urlForData: String, completion: (dictionary: NSDictionary) -> Void)
and call the completion where the data you want to "return" is available:
func jsonParserForDataUsage(urlForData: String, completion: (dictionary: NSDictionary) -> Void) {
print("json parser activated")
let urlPath = urlForData
guard let endpoint = NSURL(string: urlPath) else {
return
}
let request = NSMutableURLRequest(URL:endpoint)
NSURLSession.sharedSession().dataTaskWithRequest(request) { (data, response, error) -> Void in
do {
guard let dat = data else {
throw JSONError.NoData
}
guard let dictionary = try NSJSONSerialization.JSONObjectWithData(dat, options:.AllowFragments) as? NSDictionary else {
throw JSONError.ConversionFailed
}
completion(dictionary: dictionary)
} catch let error as JSONError {
print(error.rawValue)
} catch let error as NSError {
print(error.debugDescription)
}
}.resume()
}
Now you can use this method with a trailing closure to get the "returned" value:
jsonParserForDataUsage("http...") { (dictionary) in
print(dictionary)
}