cardigan cardigan - 1 month ago 4
JSON Question

Convert a callback Swift JSON AnyObject into a NSDictionary

I have a network connection with reads the data using JSON and gives a callback;

executeRequestURL(requestURL: url, taskCallback: {(status, resp) -> Void in

if (status == true) {
if let results = resp as? NSDictionary {
print ("\(results.count) results found")
let list = results.allValues.first as! NSArray

print (list)
}

} else {
print ("Error -- \(resp)")
}
})


This calls;

private class func executeRequestURL(requestURL: NSURL, taskCallback: @escaping (Bool, AnyObject?) -> ()) {
print ("Attempting URL -- \(requestURL)")

let request: NSURLRequest = NSURLRequest(url: requestURL as URL, cachePolicy: .reloadIgnoringLocalAndRemoteCacheData, timeoutInterval: kAPI_TIMEOUT)

let session: URLSession = URLSession.shared


let task = session.dataTask(with: request as URLRequest, completionHandler: {
(data, response, error) in

guard error == nil else {
print(error)
return
}
guard let data = data else {
print("Data is empty")
return
}

let json = try! JSONSerialization.jsonObject(with: data, options: [])
//print(json)

if let response = response as? HTTPURLResponse , 200...299 ~= response.statusCode {
taskCallback(true, json as AnyObject?)
} else {
taskCallback(false, json as AnyObject?)
}

})
task.resume()
}


The problem I have is that I want to read the results into a dictionary, loop through it and create objects.

For now, I will put my code in the executeRequestURL just to ensure it works, but I intend to seperate this code away for the required entity.

Question:

How do I read the
resp
as a dictionary?

Thanks

Sample response follows;

{
"objects": [
{
"uid": "coll_20ce39424470457c925f823fc150b3d4",
"title": "Popular",
"temp_image": "",
"body": "",
"active": true,
"slug": "popular",
"created": "2014-10-25T12:45:54+00:00",
"modified": "2014-10-25T12:45:54.159000+00:00",
"ends_on": "2100-01-01T00:00:00+00:00",
}
]
}

Answer

As the JSON is a dictionary, return a dictionary ([String:Any]) from the callback. In Swift 3 AnyObject has become Any. The strong type system of Swift encourages to be always as specific as possible.

Do a better error handling! You should return an error rather than just false.

The code uses the new Swift 3 structs URL and URLRequest

private class func executeRequestURL(requestURL: URL, taskCallback: @escaping (Bool, [String:Any]?) -> ()) {
  print ("Attempting URL -- \(requestURL)")

  let request = URLRequest(url: requestURL, cachePolicy: .reloadIgnoringLocalAndRemoteCacheData, timeoutInterval: kAPI_TIMEOUT)

  let session = URLSession.shared


  let task = session.dataTask(with: request, completionHandler: {
    (data, response, error) in

    guard error == nil else {
      print(error)
      taskCallback(false, nil)
      return
    }
    guard let data = data else {
      print("Data is empty")  // <- this will never be reached. If there is no error,
      taskCallback(false, nil) // data is always non-nil.
      return
    }
    if let response = response as? HTTPURLResponse , 200...299 ~= response.statusCode {
      let json = try! JSONSerialization.jsonObject(with: data, options: []) as!  [String:Any]
      taskCallback(true, json)
    } else {
      taskCallback(false, nil)
    }
  })
  task.resume()
}

The JSON result contains a dictionary with one key objects which contains an array of dictionaries. JSON collection types are very easy to distinguish: {} is dictionary, [] is array.


To map the JSON to objects create a struct

struct Item {

  var uid : String
  var title : String
  var tempImage : String
  var body : String
  var active : Bool
  var slug : String
  var created : String
  var modified : String
  var endOn : String
}

and an array

var items = [Item]()

Then map the dictionaries to Item

if let objects = json["objects"] as? [[String:Any]] {
  for object in objects {
    let uid = object["uid"] as! String
    var title = object["title"] as! String
    var tempImage = object["temp_image"] as! String
    var body = object["body"] as! String
    var active = object["active"] as! Bool
    var slug = object["slug"] as! String
    var created = object["created"] as! String
    var modified  = object["modified"] as! String
    var endOn  = object["end_on"] as! String
    let item = Item(uid: uid, title: title, tempImage:tempImage, body: body, active: active, slug: slug, created: created, modified: modified, endOn: endOn)
    items.append(item)

  }

The JSON values seem to come from a database which includes always all fields so the forced unwrapped values are safe.

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