Class proper not assigned in swift - request

Question

I'm doing a practice, and find my class property(adNames) can't be assigned. But it can be assigned outside(the place where I comment out). Here is my code:
import UIKit
import Alamofire
import SwiftyJSON
class AdTableViewController: UITableViewController {
var adNames: [JSON]?
override func viewDidLoad() {
super.viewDidLoad()
Alamofire.request(.GET, "http://codewithchris.com/code/afsample.json").responseJSON { (Response) -> Void in
if let value = Response.result.value{
let json = JSON(value)
print(json["secondkey"].arrayValue) //["item1","item2","item3"]
self.adNames = json["secondkey"].arrayValue
}
}
// self.adNames = ["item1", "item2", "item3"]
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
if let names = adNames {
return names.count
}
return 0
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
...
}
}
Can anybody tell me the reason? Thanks!

Answer 1

Your Alamofire request runs in the background. Meanwhile, your tableView wants to display and calls numberOfRowsInSection. By this time, Alamofire has not finished its work, so adnames hasn't been set.
You need to refresh the tableView with reloadData() after adNames is set. i.e.
Alamofire.request(.GET, "http://codewithchris.com/code/afsample.json").responseJSON { (Response) -> Void in
if let value = Response.result.value{
let json = JSON(value)
self.adNames = json["secondkey"].arrayValue
self.tableView.reloadData()
}
}
Then the tableView will refresh and re-call numberOfRowsInSection, and at this time, adNames will not be nil.

Answer 2

You are accessing self inside a closure which is passed to the request call. Use capture lists inside the closure to hold the references to the self object.
[weak self] (Response) -> Void in (in this case you have to use self? to access the self instance)
...
or [unowned self] (Response) -> Void in
If you are sure that the object will be present after the request call completes.