View is not adding subviews asynchronously Swift - ios

Question

I'm working on Swift as iOS Developer and I'm having some trouble lately adding subviews in asynchronous way, I'm using dispatch_async(dispatch_get_main_queue() but still it doesn't work. The subviews are not adding one by one and in real time but I have to wait till the call is done then the UI is updated. My goal in this is to add subviews one by one and in real time while the for loop is still going. Below is a part of my code. If somebody can help me I would really appreciate it.
for i in 0 ..< self.allChannels.count {
let param = Params().getEpgParams(String(self.allChannels[i].channelNumber))
uNetwork().httpRequestNoLoading(self.utilityClass.currentServer , parameters: param, method: uNetwork.METHOD.POST, parent: self) { (epgResponse, extra_information) -> () in
if(extra_information != uNetwork.EXTRA_INFORMATION.SUCCESS){
self.presentViewController(self.utilityClass.alert("Error", message: "An Unexpected Error Happened"), animated: true, completion: nil)
} else if(epgResponse == nil){
self.presentViewController(self.utilityClass.alert("Error", message: "Couldn't get any response from the server"), animated: true, completion: nil)
} else {
do {
var titleArray = [String]()
var start = [String]()
var end = [String]()
var progressArray = [Float]()
let jsonObject = try NSJSONSerialization.JSONObjectWithData(epgResponse, options: []) as! NSDictionary
if let response_object = jsonObject["response_object"] as? [[String: AnyObject]] {
for menu in response_object{
titleArray.append(menu["title"] as! String)
start.append(menu["programstart"] as! String)
end.append(menu["programend"] as! String)
progressArray.append(menu["progress"] as! Float)
}
if(titleArray.count > 0){
currentTitle = titleArray[0]
currentStart = start[0][start[0].startIndex.advancedBy(12)..<start[0].startIndex.advancedBy(12+4)]
currentEnd = end[0][end[0].startIndex.advancedBy(12)..<end[0].startIndex.advancedBy(12+4)]
progressValue = Float(progressArray[0] / 100)
} else {
currentTitle = "Programet e \(self.allChannels[i].title)"
currentStart = "00:00"
currentEnd = "00:00"
progressValue = 0.5
}
dispatch_async(dispatch_get_main_queue(), {
indiSub[i].removeFromSuperview()
self.contentView = UIView(frame: CGRectMake(0, ((self.scrollView.frame.height / 4) * CGFloat(i)), self.epgView.frame.width, self.scrollView.frame.height / 4))
self.contentView.layer.masksToBounds = true
self.scrollView.addSubview(self.contentView)
let button = UIButton(frame: CGRectMake(0, ((self.scrollView.frame.height / 4) * CGFloat(i)), self.epgView.frame.width, self.scrollView.frame.height / 4))
button.tag = Int(self.allChannels[i].channelNumber)
button.addTarget(self, action: #selector(LiveTvTest.playFromEpg(_:)), forControlEvents: .TouchUpInside)
self.scrollView.addSubview(button)
let currentTime = UILabel(frame: CGRectMake((self.scrollView.frame.height / 4) + 25, 0, 60, self.contentView.frame.height / 3))
if currentStart.characters.count == 4{
currentTime.text = currentStart + " |"
} else if (currentStart.characters.count == 5){
currentTime.text = currentStart + " |"
}
currentTime.font = UIFont(name: "Helvetica Neue", size: 15)
currentTime.adjustsFontSizeToFitWidth = true
currentTime.textColor = UIColor(red:0.54, green:0.13, blue:0.13, alpha:1.0)
self.contentView.addSubview(currentTime)
let nextTime = UILabel(frame: CGRectMake((self.scrollView.frame.height / 4) + 25, currentTime.frame.height, 60, self.contentView.frame.height / 3))
if nextStart.characters.count == 4{
nextTime.text = nextStart + " |"
} else if (nextStart.characters.count == 5) {
nextTime.text = nextStart + " |"
}
nextTime.font = UIFont(name: "Helvetica Neue", size: 15)
nextTime.adjustsFontSizeToFitWidth = true
nextTime.textColor = UIColor(red:0.53, green:0.53, blue:0.53, alpha:1.0)
self.contentView.addSubview(nextTime)
})
} else {
print("something went wrong with response object")
}
} catch {
self.presentViewController(self.utilityClass.alert("Error", message: "Something went wrong, please try again later"), animated: true, completion: nil)
}
}
}
}

Answer 1

If you can ensure that your closure (that you hand in to httpRequestNoLoading) is running in an arbitrary thread, you could use dispatch_sync your UI-updates into the main thread; this will wait until the work item as executed. But if the close already runs in the main thread, this will surely deadlock.
Btw. you should also dispatch the presentViewController calls into the main thread.

Answer 2

I'd guess the problem is that you're setting up a set of http calls. Those calls get executed in parallel and return via the callback. then you're making several view updates very closely together, thus, even if the code is serial, the updates happen in quick succession.
That said, the other thing to keep in mind is that osx/ios batch their ui updates. so it could be that you're putting quite a bit of work on the mainQueue at once, and aren't getting a chance to see the work happen. Why not try adding in some random delays using dispatch_after to see if that makes things pop in at different times?