UITableView reloadData not working properly - ios

Question

I'm working on an app, in which I'm calculating data in a loop and for each cycle I want to publish new section in tableview showing that calculated result. I'm adding results to an array and calling tableView.reloadData(). Problem is, the UI is not updating after each loop, but only after the last loop of the cycle and everything is done.
Some notes:
Delegation and dataSource are connected correctly, as the method is working, just not whenever I want
I also tried dispatching the whole loop into async block
I tried calling the reloadData() alone in an async block (lot's of sources advised to try this)
I tried loads of combinations including functions beginUpdates, endUpdates, reload/insert sections/rows. You get the drift.
When calling reloadData(), numberOfSections method is always called, but the cellForRow only after the whole work is done
For cells I'm using custom cells with UITableViewAutomaticDimension property on the tableView. This ensures that multiline text is shown correctly. I really want to believe my constraints on the cells are fine.
Computation code overview:
override func viewDidAppear(animated: Bool) {
for i in 0..<data.count {
// Do computationally intensive work
results[i].append(result) // multidimensional array
Util.safeInc(&doneCounter) // made thread-safe just in case with objc_sync_enter
resultTableView.reloadData()
}
}
Following are the tableView functions. I have created an expandable tableview. Also have some header functions, to create padding between sections, and selection function. They don't seem to be important here.
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
if expandedCells.contains(section) {
return results[section].count + 1
} else {
return 1
}
}
func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return doneCounter
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
if indexPath.row == 0 {
let cell = tableView.dequeueReusableCellWithIdentifier("titleCell") as! electionNameTableViewCell
cell.label.text = ...
return cell
} else {
let cell = tableView.dequeueReusableCellWithIdentifier("resultCell") as! resultTableViewCell
// set texts for cell labels
return cell
}
}
Any ideas?

Answer 1

You should call resultTableView.reloadData() on the main thread like so :
dispatch_async(dispatch_get_main_queue) {
resultTableView.reloadData()
}

Answer 2

I ended up using my own queue + dispatching reloadData() to the main queue from it.
override func viewDidAppear(animated: Bool) {
let backgroundQueue = dispatch_queue_create("com.example.workQueue", DISPATCH_QUEUE_SERIAL);
for i in 0..<data.count {
dispatch_async(backgroundQueue) {
// Do computationally intensive work
dispatch_async(dispatch_get_main_queue()) {
resultTableView.reloadData()
}
}
}
}