Tab with UITableView takes long to load - ios

Question

I have a tab that contains a UITableView. The UITableView loads JSON from a server. Here are some lines in my viewDidLoad():
// Register the UITableViewCell class with the tableView
self.tableView?.registerClass(UITableViewCell.self, forCellReuseIdentifier: self.cellIdentifier)
var tblView = UIView(frame: CGRectZero)
tableView.tableFooterView = tblView
tableView.backgroundColor = UIColor.clearColor()
startConnection()
Here is my startConnection():
func startConnection() {
let url = NSURL(string: "some correct URL")
var request = NSURLRequest(URL: url!)
var data = NSURLConnection.sendSynchronousRequest(request, returningResponse: nil, error: nil)
if data != nil {
var json = JSON(data: data!)
if let jsonArray = json.arrayValue {
for jsonDict in jsonArray {
var pageName: String? = jsonDict["title"].stringValue
//some code
}
}
activityIndicator.stopAnimating()
} else {
println("No data")
activityIndicator.stopAnimating()
var alert = UIAlertController(title: "No data", message: "No data received", preferredStyle: UIAlertControllerStyle.Alert)
let cancelAction = UIAlertAction(title: "Cancel", style: .Cancel) { (action) in
}
alert.addAction(cancelAction)
let OKAction = UIAlertAction(title: "Retry", style: .Default) { (action) in
self.startConnection()
}
alert.addAction(OKAction)
self.presentViewController(alert, animated: true, completion: nil)
}
}
After the first load, the tab will show upon clicking. I am thinking if it is the NSURLConnection.sendSynchronousRequest causing the lag. Any advice and suggestion? I don't really know how to use sendAsynchronousRequest either =/ Please help. Thank you! =D

Answer 1

Although there are several ways to get data from a website, the important thing is that you execute your UI updates on the main thread using dispatch_async(dispatch_get_main_queue()) {}. This is because URL tasks such as NSURLSession.dataTaskWithURL or NSURLConnection.sendAsynchronousRequest() {} execute on a background thread so if you don't explicitly update UI on the main thread you will often experience a lag. Here's what a simple request looks like:
func fetchJSON(sender: AnyObject?) {
let session = NSURLSession.sharedSession()
let url: NSURL! = NSURL(string: "www.someurl.com")
session.dataTaskWithURL(url) { (data, response, error) in
var rawJSON: AnyObject? = NSJSONSerialization.JSONObjectWithData(data, options: .allZeros, error: nil)
if let result = rawJSON as? [[String: AnyObject]] {
dispatch_async(dispatch_get_main_queue()) {
// Update your UI here ie. tableView.reloadData()
}
}
}.resume()
}

Answer 2

You can do it like this:
let url:NSURL = NSURL(string:"some url")
let request:NSURLRequest = NSURLRequest(URL:url)
let queue:NSOperationQueue = NSOperationQueue()
NSURLConnection.sendAsynchronousRequest(request, queue: queue, completionHandler:{ (response: NSURLResponse!, data: NSData!, error: NSError!) -> Void in
/* Your code */
})