Alexey K Alexey K - 1 month ago 16
Swift Question

How to create objects from SwiftyJSON

I have a code, that parses JSON's list of questions and I can get every property. How can I iterate through the whole file and for each question create an object ?

class ViewController: UIViewController {

var hoge: JSON?

override func viewDidLoad() {
super.viewDidLoad()

let number = arc4random_uniform(1000)
let url = NSURL(string: "http://www.wirehead.ru/try-en.json?\(number)")
var request = NSURLRequest(URL: url!)
var data = NSURLConnection.sendSynchronousRequest(request, returningResponse: nil, error: nil)
if data != nil {
hoge = JSON(data: data!)
let level = hoge!["pack1"][0]["level"].intValue
let questionText = hoge!["pack1"][0]["questionText"].stringValue
let answer1 = hoge!["pack1"][0]["answer1"].stringValue
let answer2 = hoge!["pack1"][0]["answer2"].stringValue
let answer3 = hoge!["pack1"][0]["answer3"].stringValue
let answer4 = hoge!["pack1"][0]["answer4"].stringValue
let correctAnswer = hoge!["pack1"][0]["correctAnswer"].stringValue
let haveAnswered = hoge!["pack1"][0]["haveAnswered"].boolValue

}
}
}


my model of Question which objects I want to create below

class Question {

var level : Int?
var questionText : String?
var answer1 : String?
var answer2 : String?
var answer3 : String?
var answer4 : String?
var correctAnswer : String?
var haveAnswered : Bool = false

init(level: Int, questionText:String, answer1:String, answer2:String, answer3:String, answer4:String, correctAnswer: String, haveAnswered:Bool) {
self.level = level
self.questionText = questionText
self.answer1 = answer1
self.answer2 = answer2
self.answer3 = answer3
self.answer4 = answer4
self.correctAnswer = correctAnswer
self.haveAnswered = false
}

}

Answer

This is how I would approach the problem.

Step 1

Since your init inside Question does receive non optional objects, I had the feeling that the properties of Questions should be non optional too. I also converted the properties from var to let (tell me if I am wrong).

Step 2

This is the refactored Question class. As you can see I added a class method build that receive a JSON (a SwiftyJSON) and returns a Question (if the json contains correct data), nil otherwise.

Right now I cannot do this with a failable initializer.

extension String {
    func toBool() -> Bool? {
        switch self.lowercaseString {
        case "true", "1", "yes" : return true
        case "false", "0", "no" : return false
        default: return nil
        }
    }
}

class Question {

    let level: Int
    let questionText: String
    let answer1: String
    let answer2: String
    let answer3: String
    let answer4: String
    let correctAnswer: String
    let haveAnswered: Bool

    init(level: Int, questionText:String, answer1:String, answer2:String, answer3:String, answer4:String, correctAnswer: String, haveAnswered:Bool) {
        self.level = level
        self.questionText = questionText
        self.answer1 = answer1
        self.answer2 = answer2
        self.answer3 = answer3
        self.answer4 = answer4
        self.correctAnswer = correctAnswer
        self.haveAnswered = false
    }

    class func build(json:JSON) -> Question? {
        if let
            level = json["level"].string?.toInt(),
            questionText = json["questionText"].string,
            answer1 = json["answer1"].string,
            answer2 = json["answer2"].string,
            answer3 = json["answer3"].string,
            answer4 = json["answer4"].string,
            correctAnswer = json["correctAnswer"].string,
            haveAnswered = json["haveAnswered"].string?.toBool() {
                return Question(
                    level: level,
                    questionText: questionText,
                    answer1: answer1,
                    answer2: answer2,
                    answer3: answer3,
                    answer4: answer4,
                    correctAnswer: correctAnswer,
                    haveAnswered: haveAnswered)
        } else {
            debugPrintln("bad json \(json)")
            return nil
        }
    }
}

Step 3

Now let's look at viewDidLoad.

func viewDidLoad() {
    super.viewDidLoad()

    let number = arc4random_uniform(1000)

    if let
        url = NSURL(string: "http://www.wirehead.ru/try-en.json?\(number)"),
        data = NSURLConnection.sendSynchronousRequest(NSURLRequest(URL: url), returningResponse: nil, error: nil) {
        // line #a
        let rootJSON = JSON(data: data) 
        // line #b
        if let questions = (rootJSON["pack1"].array?.map { return Question.build($0) }) {
            // now you have an array of optional questions [Question?]...
        }

    }
}

At line #a I put inside rootJSON the whole data received from the connection (converted into JSON).

What happen at line #b?

Well I try to access the array located inside "pack1".

rootJSON["pack1"].array?

If the array exists I run the map method. This will extract each cell of the array and I will be able to refer to it with the $0 parameter name inside the closure.

Inside the closure I use this json block (that should represent a question) to build a Question instance.

The result will be an array of Question?. There could be ill values if some son data was not valid. If you want I can show you how to remove the nil values from this array

I could not try the code with real data, hope this helps.