swift & json: array of objects

Question

I am trying to convert json array of objects to a Dictionary,

I have this code:

func load() { //this function is the first that is executed

    getActivities {
        (response) in
        self.loadActivities(response as NSArray)
    }
}

func getActivities(callback:(NSDictionary) -> ()){ //the next url contains the json array of objects
    request("http://localhost/llancaActivity/public/activity/getListJSON/0/2", callback: callback)
}

func request(url:String, callback:(NSDictionary) -> ()){
    var nsURL : NSURL = NSURL(string: url)!;

    let task = NSURLSession.sharedSession().dataTaskWithURL(nsURL){
        (data, response, error) in
        var error: NSError?
        var response = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &error) as NSDictionary;

        callback(response);
    }

    task.resume();
}


func loadActivities(activities:NSArray){
    for activity in activities {
        println(activity["id"]); //<-- These line never is executed!!!! 
    }
}

If I visit with my browser the next URL: http: // localhost/llancaActivity/public/activity/getListJSON/0/2

I have the next response:

 [{"id":"3","title":"Confer\u00e8ncia de meteorologia \u201cEl canvi clim\u00e0tic\u201d","description":"Hora: 19h\nLloc: Sala de Confer\u00e8ncies de la Casa de Cultura","start_date":"2014-12-13","end_date":"2014-12-13","id_category":null},{"id":"4","title":"Espectacle a favor de la Marat\u00f3 de TV3","description":"Hora: 17h\nEntrada: la voluntat\nLloc: Sala d\u2019Actes de la Casa de Cultura\nOrganitza: Associaci\u00f3 de Puntaires de Llan\u00e7\u00e0\nCol\u00b7labora: Entitats i Associacions de Llan\u00e7\u00e0 i l\u2019Ajuntament de Llan\u00e7\u00e0","start_date":"2014-12-13","end_date":"2014-12-13","id_category":null}]

Please, sorry for my english...

Did you inspect the response and error variables? What do they contain? — Aaron Brager
– Aaron Brager, Commented Dec 13, 2014 at 1:22

Rob · Accepted Answer · 2014-12-13 02:28:16Z

You are trying to return a dictionary representation of your JSON, but it's not a dictionary. It's an array. Yes, it's an array of dictionaries, but that's a very different thing than a simple dictionary.

So the JSON parsing is simply:

let responseObject = NSJSONSerialization.JSONObjectWithData(data!, options: nil, error: &parseError) as NSArray

Integrating that into your request function, it looks like:

func request(urlString: String, callback: (responseObject: NSArray?, error: NSError?) -> ()) {
    let url = NSURL(string: urlString)!

    let task = NSURLSession.sharedSession().dataTaskWithURL(url) {
        data, response, error in

        if data == nil {
            callback(responseObject: nil, error: error)
        } else {
            var parseError: NSError?
            let responseObject = NSJSONSerialization.JSONObjectWithData(data!, options: nil, error: &parseError) as? NSArray
            callback(responseObject: responseObject, error: parseError)
        }
    }
    task.resume()
}

Note:

I changed the closure to return two parameters, the responseObject and an error (that way the caller can detect errors), but that's up to you.
I cast the NSJSONSerialization result to an NSArray, not a NSDictionary.
More accurately, I actually cast it to an optional array (using as?), so it will gracefully handle any parsing errors.

Alternatively, you could make this return a Swift array of Swift dictionaries:

func request(urlString: String, callback: (responseObject: [[String: AnyObject]]?, error: NSError?) -> ()) {
    let url = NSURL(string: urlString)!

    let task = NSURLSession.sharedSession().dataTaskWithURL(url) {
        data, response, error in

        if data == nil {
            callback(responseObject: nil, error: error)
        } else {
            var parseError: NSError?
            let responseObject = NSJSONSerialization.JSONObjectWithData(data!, options: nil, error: &parseError) as? [[String: AnyObject]]
            callback(responseObject: responseObject, error: parseError)
        }
    }
    task.resume()
}

Clearly, whatever you change the request closure to, you'd want to make the same change to getActivities, but that should be self explanatory.

hd1 · Accepted Answer · 2014-12-13 02:27:22Z

0

With swifty, you only need to issue the following stanza to convert a json array of dicts to an object:

let data = "[{\"id\":\"3\",\"title\":\"Confer\u00e8ncia de meteorologia \u201cEl canvi clim\u00e0tic\u201d\",\"description\":\"Hora: 19h\nLloc: Sala de Confer\u00e8ncies de la Casa de Cultura\",\"start_date\":\"2014-12-13\",\"end_date\":"2014-12-13\",\"id_category\":null}" // .... and the rest of your JSON
let json = JSON(data:data)

Now json will have the parsed data.

edited Dec 13, 2014 at 2:27

answered Dec 13, 2014 at 1:23

hd1

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