calling self.tableView.reloadData takes 10-15 seconds

Question

I am trying to load data into a Table View with Swift. My problem is that the displaying of the data takes a good 10-15 seconds. The data does end up getting displayed, but it just takes to long of a time. I am retrieving events from iCal and then displaying them in a table view. Is there a problem with the code?

class EventsViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {

    @IBOutlet weak var eventCounterLabel: UILabel!
    @IBOutlet weak var tableView: UITableView!

    var eventStore = EKEventStore()
    var calendar: EKCalendar?
    var events = NSMutableArray() as NSMutableArray
    var times = NSMutableArray() as NSMutableArray

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)

        //Table View Data Source and Delegate
        self.tableView.delegate = self
        self.tableView.dataSource = self

        //Event Kit access
        eventStore.requestAccessToEntityType(EKEntityTypeEvent,
            completion: {(granted: Bool, error:NSError!) in
                if !granted {
                    println("Access to store not granted")
                }else{
                    self.getTheCalendar()
                }
        })
    }

    //Event Kit Methods
    func getTheCalendar(){
        //Set the start and finish dates for events
        let start = NSDate() as NSDate
        let finish = NSDate() as NSDate

        //Make the predicate
        let eventPredicate =     self.eventStore.predicateForEventsWithStartDate(start, endDate: finish, calendars: nil) as NSPredicate

       self.eventStore.enumerateEventsMatchingPredicate(eventPredicate, usingBlock: { (event: EKEvent!, stop: UnsafeMutablePointer<ObjCBool>) -> Void in
            if event != nil{
                self.events.addObject(event.title)
                self.times.addObject(event.startDate)
            }

            //Set the event counter label
            if self.events.count == 1{
                self.eventCounterLabel.text = "You have " + "\(self.events.count)" + " event today."
            }else{
                self.eventCounterLabel.text = "You have " + "\(self.events.count)" + " events today."
            }

            //Reload the table view
            self.tableView.reloadData()
        })
    }

    //Table View Methods
    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return self.events.count
    }

    func tableView(tableView: UITableView, cellForRowAtIndexPath  indexPath: NSIndexPath) -> UITableViewCell {
        var cell:EventsTableViewCell =   self.tableView.dequeueReusableCellWithIdentifier("Cell") as   EventsTableViewCell

        //Set the event label
        cell.eventLabel.text = (self.events.objectAtIndex(indexPath.row) as String)

        cell.eventLabel.adjustsFontSizeToFitWidth = true

        //Set the event time label
        let calendar = NSCalendar.currentCalendar()
        let components = calendar.components(.CalendarUnitHour | .CalendarUnitMinute, fromDate:self.times.objectAtIndex(indexPath.row) as NSDate)

        let hour = components.hour as Int

        var theHourOfTheEvent = hour
        if theHourOfTheEvent < 12{

            if theHourOfTheEvent == 0{

                cell.eventTimeLabel.text = "All Day"

            }else{

                cell.eventTimeLabel.text = "\(theHourOfTheEvent)" + " am"

            }

        }else if theHourOfTheEvent > 12 && theHourOfTheEvent < 24{

            theHourOfTheEvent -= 12

            cell.eventTimeLabel.text = "\(theHourOfTheEvent)" + " pm"

        }else if theHourOfTheEvent == 24{

            theHourOfTheEvent -= 12

            cell.eventTimeLabel.text = "\(theHourOfTheEvent)" + " am"

        }else if theHourOfTheEvent > 24{

            theHourOfTheEvent -= 24

            cell.eventTimeLabel.text = "\(theHourOfTheEvent)" + " am"

        }else if theHourOfTheEvent == 12{

            cell.eventTimeLabel.text = "\(theHourOfTheEvent)" + " pm"

        }

        return cell
    }

    func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
        return 100.0
    }

    func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

    }
}

Answer 1

You are reloading the table view inside the EventKit enumerator.

   self.eventStore.enumerateEventsMatchingPredicate(eventPredicate, usingBlock: { 
        ...
        self.tableView.reloadData()
    })

This means you reload it once for each retrieved event in the calendar - which is likely to be a lot of un-necessary reloads, and slow.

You should only call this function once, after all the events are collected. Move it outside the loop and you should see an improvement.

   self.eventStore.enumerateEventsMatchingPredicate(eventPredicate, usingBlock: { 
        ...
    })
    self.tableView.reloadData()

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You may also want to call it in a dispatch block on the main thread; Calls to change the UI should always be on the main thread, and it's unclear from your example what thread is executing the code.

---

Alternatively, you might want to add the elements to the table as soon as you get them - in this case, don't use reloadTable, but use insertRowsAtIndexPaths as you get the new data. This is cheaper than calling reloadData every time, since it doesn't visit every cell - and in fact will only visit on-screen cells, which is cheap assuming you add new events to the end of the list (not the start).