Global variable doesn't store any data in anonymous method - ios

Question

trying to get nasa.gov asteroid's data. There is a asteroids global variable of array of Asteroid instances. There is about 1000 occurrences in the jsonData variable. When I append the occurrence at the line self.asteroids.append(), I can see it's adding. When the anonymous completionHandler method ends, variable self.asteroids is empty again, so it doesn't reload no data.
It doesn't make any sense to me since asteroids is a global variable and it should store any data appended to it. Can anyone help?
class ViewController: UITableViewController {
var asteroids = [Asteroid]()
override func viewDidLoad() {
super.viewDidLoad()
let connectionString: String = "https://data.nasa.gov/resource/y77d-th95.json"
let url = NSURL(string: connectionString)!
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithURL(url, completionHandler: { (data: NSData?, response: NSURLResponse?, error: NSError?) in
do {
let jsonData = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions())
for index in 0 ... (jsonData.count - 1) {
self.asteroids.append(Asteroid(name: jsonData[index]["name"] as! NSString as String))
}
} catch {
print("Error")
return
}
})
task.resume()
self.tableView.reloadData()
}

Answer 1

Put the table view's reloadData method in the completion block, after the asteroids array has been modified.
Another way would be to reloadData in asteroid didSet method:
var asteroids = [Asteroid]() {
didSet {
dispatch_async(dispatch_get_main_queue()) {
self.tableView.reloadData()
}
}
}
Code of the completion handler is called after the end of scope of viewDidLoad function. Because the dataTaskWithURL is an asynchronous operation.

Answer 2

Is it empty or you're reloading the table view before the dataTask finishes?
Try to move the reloadData inside the completion closure:
override func viewDidLoad() {
super.viewDidLoad()
let connectionString: String = "https://data.nasa.gov/resource/y77d-th95.json"
let url = NSURL(string: connectionString)!
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithURL(url, completionHandler: { (data: NSData?, response: NSURLResponse?, error: NSError?) in
do {
let jsonData = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions())
for index in 0 ... (jsonData.count - 1) {
self.asteroids.append(Asteroid(name: jsonData[index]["name"] as! NSString as String))
}
self.tableView.reloadData()
} catch {
print("Error")
return
}
})
task.resume()
}
UPDATE: A second approach, if you're 100% sure you want the tableView to be updated after all data has been downloaded & parsed could be:
override func viewDidLoad() {
super.viewDidLoad()
let connectionString: String = "https://data.nasa.gov/resource/y77d-th95.json"
let url = NSURL(string: connectionString)!
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithURL(url, completionHandler: { (data: NSData?, response: NSURLResponse?, error: NSError?) in
do {
let jsonData = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions())
for index in 0 ... (jsonData.count - 1) {
self.asteroids.append(Asteroid(name: jsonData[index]["name"] as! NSString as String))
}
self.tableView.delegate = self
self.tableView.dataSource = self
} catch {
print("Error")
return
}
})
task.resume()
}