PerformSegueWithIdentifier not working Swift - ios

Question

I have a tableView on my page and when I press a specific row, my app is supposed to show another page using segue. However when i click on the appropriate row it freezes, and then when I click a different row the segue finally shows up, which is odd. The code used to work for me but for some reason stopped, and I can't identify the issue because the code is identical (at least as far as I can see). Here is a code snippet :
func restClient(client: DBRestClient!, loadedFile destPath: String!, contentType: String!, metadata: DBMetadata!){
let title = "This format is incorrect"
let message = "You can only download file that is in .txt format"
let okText = "OK"
let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.Alert)
let okayButton = UIAlertAction(title: okText, style: UIAlertActionStyle.Cancel, handler: nil)
alert.addAction(okayButton)
if contentType.rangeOfString("text") != nil{
print("this is text")
self.performSegueWithIdentifier("segue", sender: nil)
}
else{
print("this is an error")
presentViewController(alert, animated: true, completion: nil)
return;
}
let documentsDirectoryPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as! NSString
print("The file \(metadata.filename) was downloaded. Content type: \(contentType). The path to it is : \(documentsDirectoryPath)" )
progressBar.hidden = true
let documentsURL = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)[0]
let localFilePath = documentsURL.URLByAppendingPathComponent("Documents")
let checkValidation = NSFileManager.defaultManager()
if (checkValidation.fileExistsAtPath(localFilePath.path!))
{
print("FILE AVAILABLE");
}
else
{
print("FILE NOT AVAILABLE");
}
return
}
didDeselectRowAtIndexPath code :
func tableView(tableView: UITableView, didDeselectRowAtIndexPath indexPath: NSIndexPath){
let selectedFile: DBMetadata = dropboxMetadata.contents[indexPath.row] as! DBMetadata
let documentsDirectoryPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0]
let localFilePath = (documentsDirectoryPath as NSString).stringByAppendingPathComponent(selectedFile.filename)
print("The file to download is at: \(selectedFile.path)")
print("The documents directory path to download to is : \(documentsDirectoryPath)")
print("The local file should be: \(localFilePath)")
showProgressBar()
dbRestClient.loadFile(selectedFile.path, intoPath: localFilePath as String)
}
The picture below illustrates when I click on the file.txt row. As you can see it just stays grey and nothing happens, but after that, if I click on another file, say enumrec.pdf, it will show the appropriate page. Would be happy if anyone could point out what i am doing wrong here.

Answer 1

You should use didSelectRowAtIndexPath instead of didDeselectRowAtIndexPath. The latest is often propose first when using autocompletion, it's easy to make the mistake.

Answer 2

It looks like you are performing your seque after your data call which is on a different thread (so your app can carry on when your data call is running). When you change UI you have to run it on the main thread otherwise you can have issues like this. Just wrap your performSegue code in this:
dispatch_async(dispatch_get_main_queue(),{
self.performSegueWithIdentifier("segue", sender: nil)
});
You can read about threads/backgrounds tasks etc here:
https://developer.apple.com/library/mac/documentation/General/Conceptual/ConcurrencyProgrammingGuide/OperationQueues/OperationQueues.html