Passing an NSMutableArray to another object in Swift

Question

I'm making a network call and retrieving some information from an API and storing it in an NSMutableArray. I hit a wall when trying to send that array info over to another object:
I don't have any errors. I am not able to access the array information in another class. It prints fine in the API class but when trying to access in another class the array prints empty.

This is my API class with an NSMutableArray at the very top to hold the info:

class API: NSObject {

    var informationArray = NSMutableArray();

    func getEarthquakeInformation() {

        let session = NSURLSession.sharedSession()
        let urlString = "http://ehp2-earthquake.wr.usgs.gov/fdsnws/event/1/query?format=geojson&limit=20"
        let url = NSURL(string: urlString)!
        let request = NSURLRequest(URL: url)
        let task = session.dataTaskWithRequest(request){ data,response,downloadError in

            if let error = downloadError {
                 print("could not complete the request\(error)")
            } else {

                let parsedResult = try! NSJSONSerialization.JSONObjectWithData(data! , options: NSJSONReadingOptions.AllowFragments)
                let dataDict = parsedResult as! NSDictionary

                // This holds all the information we need from the API.
                if let result = dataDict["features"] {

                    for var i = 0; i < result.count; i++ {
                        self.informationArray.addObject(result[i])
                        print(self.informationArray[i]) 
                    }

                } else {
                    print("error")
                }

                //print("info from the array \(self.informationArray)")   
            }  
        }
        task.resume() 
    }
}

And this is the class I'm trying to send it over to: MapViewController

 override func viewDidLoad() {
        super.viewDidLoad()

        // Instance of the api class
        let apiObject = API()
        apiObject.getEarthquakeInformation()
        print(apiObject.informationArray)

Your call (NSURLSession thing) is async. You'd print "print(apiObject.informationArray)" before "print(self.informationArray[i])". Use a block (closure I think in Swift) — Larme
– Larme, Commented Jan 20, 2016 at 15:27
i dont have any errors. I am not able to access the array information in another class. it prints fine in the api class but when trying to access in another class the array prints empty. — lipizr
– lipizr, Commented Jan 20, 2016 at 15:47

raf · Accepted Answer · 2016-01-20 15:40:53Z

1

Several things here:

First, please look into using a networking library (such as AlamoFire)

Second, when you declare your mutable array, you should do it in this form (No reason to use NSMutableArray()):

var myArray = [ObjectType]()

Third, don't use C-style for-loops, they're flagged to be removed from Swift. You should iterate instead:

for item in result {
    //Do something with item.
}

Also, as far as "sending" the array to your MapViewController object. If the API object lives in your MapViewController, then you could have your API function take in a closure as an argument. You can pass the array back to the MapViewController in the closure itself. Or you could also use notifications.

Hope this helps.

edited Jan 20, 2016 at 15:40

answered Jan 20, 2016 at 15:33

raf

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Comments

Ismail · Accepted Answer · 2016-01-20 16:07:27Z

  let apiObject = API()
    // Your problem it here this method takes time to update informationArray
    apiObject.getEarthquakeInformation()
    // But this line print immediately while it's still empty.
    print(apiObject.informationArray)

what you do is

remove informationArray from the API class at all and put it in MapViewController

change getEarthquakeInformation method to have a compeletion handler

class API: NSObject {

// remove it  //var informationArray = NSMutableArray();

func getEarthquakeInformation(compeletion: (informationArray: [AnyObject]!) ->()) {

    let session = NSURLSession.sharedSession()
    let urlString = "http://ehp2-earthquake.wr.usgs.gov/fdsnws/event/1/query?format=geojson&limit=20"
    let url = NSURL(string: urlString)!
    let request = NSURLRequest(URL: url)
    let task = session.dataTaskWithRequest(request){ data,response,downloadError in

        if let error = downloadError {
             print("could not complete the request\(error)")
        } else {

            let parsedResult = try! NSJSONSerialization.JSONObjectWithData(data! , options: NSJSONReadingOptions.AllowFragments)
            let dataDict = parsedResult as! NSDictionary

            // This holds all the information we need from the API.
            if let result = dataDict["features"] {
              compeletion(result)
            } else {
                print("error")
            }
        }    
    }

    task.resume()
}

and then in MapViewController

var informationArray: [AnyObject]!
override func viewDidLoad() {
   super.viewDidLoad()

    // Instance of the api class
    let apiObject = API()
    apiObject.getEarthquakeInformation() { [unowned self] (result) ->() in 
    self.inforamtionArray = result
    print(self.informationArray)
}

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