Cannot add element to array

Question

I'm new in Swift and I have issue with adding an element to an Array

I'm trying to store 6 objects from JSON to Array. But the Array is nil.

I see it add to Array when I debug it, I have no idea why it's nil after finished request JSON?

JSON:

[
    {
        "amount": "20.0",
        "date": "10/07/2016"
    },
    {
        "amount": "21.0",
        "date": "11/07/2016"
    },
    {
        "amount": "16.0",
        "date": "12/07/2016"
    },
    {
        "amount": "30.0",
        "date": "13/07/2016"
    },
    {
        "amount": "50.0",
        "date": "14/07/2016"
    },
    {
        "amount": "33.0",
        "date": "15/07/2016"
    }
]

Service:

    class DownloadService {
    static let instance = DownloadService()
    //static var goldArray = [Gold]()
    var goldArray = [Gold]()
    func getData() {
        Alamofire.request("https://rth-recruitment.herokuapp.com/api/prices/chart_data", headers: headers).responseJSON { response in
            if let objJson = response.result.value as! NSArray?{
                for element in objJson {
                    let data = element as! NSDictionary
                    let amount = data["amount"] as! String
                    let date = data["date"] as! String
                    let gold = Gold(amount: amount, date: date)
                    self.goldArray.append(gold)
                    print(self.goldArray.count)//print 1 to 6
                }
            }
        }
        printGoldArray()
    }

    func printGoldArray(){
        for element in self.goldArray {
            print(element)//print nothing
        }
    }
}

Gold class:

    class Gold{
    let amount:String
    let date: String

    init(amount: String, date: String) {
        self.amount = amount
        self.date = date
    }

}

ViewController:

    class ViewController: UIViewController {
    //var dataArray = [Gold]()
    override func viewDidLoad() {
        super.viewDidLoad()
        DownloadService.instance.getData()

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

It's because you are missing the asynchronous concept. If you add print("in alamofire closure") before print(self.goldArray.count) and print("calling print") just before printGoldArray(), you'll see that the order of the print is no the one you expect. Look for "Swift + Closure + Async". — Larme
– Larme, Commented Jul 6, 2017 at 10:36
Why do you forced unwrap an optional to an optional (as! NSArray?) ?? — vadian
– vadian, Commented Jul 6, 2017 at 10:41

Aravind A R · Accepted Answer · 2017-07-06 10:37:17Z

1

Here printGoldArray function is being called from outside the closure which means when printGoldArray is called the goldArray may not be having any values.

Try calling printGoldArray function from inside the closure after adding the values. Try the below code

func getData() {
    Alamofire.request("https://rth-recruitment.herokuapp.com/api/prices/chart_data", headers: headers).responseJSON { response in
        if let objJson = response.result.value as! NSArray?{
            for element in objJson {
                let data = element as! NSDictionary
                let amount = data["amount"] as! String
                let date = data["date"] as! String
                let gold = Gold(amount: amount, date: date)
                self.goldArray.append(gold)
                print(self.goldArray.count)//print 1 to 6
            }
        }
     printGoldArray()
    }

}

answered Jul 6, 2017 at 10:37

Aravind A R

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6 Comments

KhanhNg Over a year ago

Actually, my purpose is use goldArray[] at other method, so I declared it as global var but till cannot get data. So is there any way to use it?

Aravind A R Over a year ago

You can use closure in the func getData() also and on its completion closure you can use the goldArray

KhanhNg Over a year ago

Can I use outside of func getData()?

Aravind A R Over a year ago

Yup you can use goldArray outside getData but only after the execution of the alamofire's completion block/closure

KhanhNg Over a year ago

is it why my goldArray[] nil at that time? How can I know the execution of the Alamofire closure is completed?

|

Fangming · Accepted Answer · 2017-07-06 10:51:04Z

0

You need to parse your JSON data first before getting value out

do{
    let json = try JSONSerialization.jsonObject(with: response.result.value, options: []) as? [Any]
    let firstObj = json?[0] as! [String: String]
    let amount = firstObj["amount"]
    dump(amount)
}catch let error{

}

Then, your HTTP call will not get you the return value until the closure is executed. So to print your array, you need to do it inside your closure. For example, you can do so right after the json parsing, by calling printGoldArray()

edited Jul 6, 2017 at 10:51

answered Jul 6, 2017 at 10:37

Fangming

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Comments

Jaydeep Vora · Accepted Answer · 2017-07-06 11:36:14Z

First, your array is not print array element because you print it directly after closure. closure uses async paradigm. so put the print function inside closure.

and Second thing is why use to much force full unwrap. instead you can use if let or guard statement

you can see below code.

func getData() {
        Alamofire.request("https://rth-recruitment.herokuapp.com/api/prices/chart_data", headers: headers).responseJSON { response in
            if let objJson = response.result.value as? NSArray {
                for element in objJson {
                    if let data = element as? NSDictionary {
                        let amount = data["amount"] as! String
                        let date = data["date"] as! String
                        let gold = Gold(amount: amount, date: date)
                        self.goldArray.append(gold)
                        print(self.goldArray.count)
                    }
                }
            }
            printGoldArray()
        }
    }

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