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Swift UITableView reloadData in a closure

Posted by: admin November 30, 2017 Leave a comment

Questions:

I believe I’m having an issue where my closure is happening on a background thread and my UITableView isn’t updating fast enough. I am making a call to a REST service and in my closure i have a tableView.reloadData() call but it takes a few seconds for this to happen. How do I make the data reload faster (perhaps on the main thread?)

REST Query Function – using SwiftyJSON library for Decoding

func asyncFlightsQuery() {
    var url : String = "http://127.0.0.1:5000/flights"
    var request : NSMutableURLRequest = NSMutableURLRequest()
    request.URL = NSURL(string: url)
    request.HTTPMethod = "GET"

    NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue(), completionHandler:{ (response:NSURLResponse!, networkData: NSData!, error: NSError!) -> Void in
        var error: AutoreleasingUnsafeMutablePointer<NSError?> = nil


        // Parse with SwiftyJSON
        let json = JSON(data: networkData)

        // Empty out Results array
        self.resultArray = []

        // Populate Results Array
        for (key: String, subJson: JSON) in json["flights"] {
            print ("KEY: \(key) ")
            print (subJson["flightId"])
            print ("\n")

            self.resultArray.append(subJson)
        }

        print ("Calling reloadData on table..??")
        self.tableView.reloadData()


    })
}

Once self.tableView.reloadData() is called in my debugger

Answers:

UIKit isn’t thread safe. The UI should only be updated from main thread:

dispatch_async(dispatch_get_main_queue()) {
    self.tableView.reloadData()
}

Update. In Swift 3 and later use:

DispatchQueue.main.async {
    self.tableView.reloadData()
}

Questions:
Answers:

You can also reload UITableView like this

self.tblMainTable.performSelectorOnMainThread(Selector("reloadData"), withObject: nil, waitUntilDone: true)

Questions:
Answers:

With Swift 3 use

DispatchQueue.main.async {
    self.tableView.reloadData()
}

Questions:
Answers:

SWIFT 3:

OperationQueue.main.addOperation ({
     self.tableView.reloadData()
})

Questions:
Answers:

You can also update the main thread using NSOperationQueue.mainQueue(). For multithreading, NSOperationQueue is a great tool.

One way it could be written:

NSOperationQueue.mainQueue().addOperationWithBlock({
     self.tableView.reloadData()       
})

Update: DispatchQueue is the way to go for this

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