UITableView重新加载数据不起作用

Question

I have a simple iOS application written in Swift that loads JSON data downloaded over the Internet and displays it into a UITableView. When I launch the application for the first time, everything works correctly and the table displays the correct information.

In my app, I have a button that triggers a refresh when I would like to reload the data. So I call the displayTable() method when the refresh button is tapped which downloads the data again and then calls the tableView.reloadData() method on the main thread to refresh the data but the reload does not appear to work. I manually change the data on the server and hit refresh but I still have the old data cached in my application. I can exit/kill the application and the old data stays 'stuck' forever unless I delete the app and reinstall.

I've attached the code for my ViewController below. I've spent way too many hours looking at this and I cannot seem to find why the reloadData doesn't work. Any ideas, hints would be greatly appreciated.

thanks

--Vinny

class ViewController: UITableViewController {

    var tableData = []

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func viewWillAppear(animated: Bool) {
        println("viewWillAppear was just called")
        super.viewWillAppear(true)

        self.displayTable()
    }

    func displayTable() {
        getJSONData("http://www.example.com/data.json") { (results, resultError) in

            if (resultError == nil) {
                if var results = results {
                    dispatch_async(dispatch_get_main_queue(), {
                        self.tableData = [] //create out data on subsequent refreshes
                        self.tableData = results
                        self.tableView.reloadData() //This doesn't appear to be working!
                    })
                } else {
                    self.displayErrorPopup()
                }
            } else {
                self.displayErrorPopup()
            }
        }
    }

    func displayErrorPopup() {
        let alertViewController = UIAlertController(title: "Error", message: "Couldn't connect to API", preferredStyle: .Alert)
        let okButton = UIAlertAction(title: "OK", style: .Default, handler: nil)
        let cancelButton = UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)
        alertViewController.addAction(okButton)
        alertViewController.addAction(cancelButton)
        self.presentViewController(alertViewController, animated: true, completion: nil)
    }

    //todo - extract this method into it's own class
    func getJSONData(ttAPIURL : String, completion: (resultsArray: NSArray?, resultError: NSError?) -> ()){
        let mySession = NSURLSession.sharedSession()
        let url: NSURL = NSURL(string: ttAPIURL)!

        let networkTask = mySession.dataTaskWithURL(url, completionHandler : {data, response, error -> Void in
            var err: NSError?
            if (error == nil) {
                var theJSON = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &err) as NSMutableDictionary
                let results : NSArray = theJSON["list"]!["times"] as NSArray
                completion(resultsArray: results, resultError: error)
            } else {
                completion(resultsArray: nil, resultError: error)
            }
        })
        networkTask.resume()
    }

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return tableData.count
    }

    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCellWithIdentifier("ttCell", forIndexPath: indexPath) as UITableViewCell
        let timesEntry = self.tableData[indexPath.row] as NSMutableDictionary
        cell.textLabel.text = (timesEntry["routeName"] as String)
        return cell
    }

    override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        return 1
    }

    @IBAction func refreshButtonTap(sender: AnyObject) {
        self.displayTable()
    }    
}

Answer 1

Ok, so you say that reloadData is not working but that is almost certainly not your problem. To debug this you should:

1. Make sure reloadData is actually being called (breakpoint or println )
2. Check if the UITableViewDataSource methods are being called after you call reloadData (breakpoint or println)
3. Check the results array that you are getting back from the network request (probably println(results) )

My guess is that it is failing at number 3 which means it has nothing to do with reloadData. Perhaps the shared NSURLSession has caching enabled? Try setting mySession.URLCache to nil .

Answer 2

Try to replace it

override func viewWillAppear(animated: Bool) {
    println("viewWillAppear was just called")
    super.viewWillAppear(true)
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), { () -> Void in
        self.displayTable()
    })
}

Answer 3

Thanks drewag and Jirom for your answers. Great comments that were very helpful. I just found my problem and its something I should have thought about earlier. The domain which is hosting my dynamic JSON data is being protected by CloudFlare and it appears that my pages rules to disable caching for a certain directory aren't working. So all of the JSON content was being cached and that was the reason my application wouldn't show the new data.

Thanks again guys for your responses.

--Vinny

PS: Per Drewag's suggestion, I added an instance of NSURLSessionConfiguration which defines the behavior and policies to use when downloading data using an NSURLSession object, and set the URLCache property to nil to disable caching.

let config = NSURLSessionConfiguration.defaultSessionConfiguration()
config.URLCache = nil
let mySession = NSURLSession(configuration: config)