直到在iOS中选中，UITableView中的单元格才会更新（快速）

Question

I'm developing an app with Parse that has a tableview with cells containing a label that has mutual friends from Facebook, my problem is that everything thing in the table works fine but the mutual friends label, it takes long to show unless I select the row (when I select the row the number appears immediately).. Here's my code for getting the mutual friends and setting the label in the cell:

let facebookContext = driverobj?.objectForKey("facebookContext") as! String
let user: PFUser = PFUser.currentUser()!
let access_token = user.valueForKey("authData")?.valueForKey("facebook")?.valueForKey("access_token") as! String
let usercontexturl: NSURL = NSURL(string: "https://graph.facebook.com/\(facebookContext)/mutual_friends?access_token=\(access_token)")!

let myrequest: NSURLRequest = NSURLRequest(URL: usercontexturl)
let mysession = NSURLSession.sharedSession()
let task = mysession.dataTaskWithRequest(myrequest) { data, response, error in
        print("Task completed")
        do {
             let jsonresult = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers)
             cell.mutualFriendsLabel?.text = (jsonresult.valueForKey("summary")?.valueForKey("total_count"))!.stringValue + " Mutual Friends"

        } catch {
             print(error)
        }
}
task.resume()

This code is inside cellForRowAtIndexPath method, and didSelectRowAtIndexPath method in empty.

Answer 1

The block passed to dataTaskWithRequest is probably not executing on the main thread which can cause these types of symptoms to appear. Try executing the UI updates to the main thread like:

dispatch_async(dispatch_get_main_queue()) {
    cell.mutualFriendsLabel?.text = (jsonresult.valueForKey("summary")?.valueForKey("total_count"))!.stringValue + " Mutual Friends"
}

Answer 2

I think you need to update UI on main queue like this:

dispatch_async_(your_queue) {
    task.response {
        //handle data
        dispatch_async(dispatch_get_main_queue()) {
            //update UI, etc. change label text
        }
    }
}