mysterious UIActivityIndicatorView error? - ios

Question

I've been getting an EXC_BAD_ACCESS error/crash when I engage in a specific action within my application. Figuring that this was a memory management issue, I enabled NSZombies to help me decipher the issue. Upon the crash, my console gave me the following message:
heres my stack trace:
and the new error highlighting my app delegate line:
Now being the debugger is referring to a UIActivityIndicatorRelease, and the only line of code highlighted in my stack trace is the 1st line in my delegate, is there an issue with my Activity Indicator UI Element? Here is the logic within my login action ( which forces the crash every time ):
#IBAction func Login(sender: AnyObject) {
activityIND.hidden = false
activityIND.startAnimating()
var userName = usernameText.text
var passWord = passwordText.text
PFUser.logInWithUsernameInBackground(userName, password: passWord) {
(user, error: NSError?) -> Void in
if user != nil {
dispatch_async(dispatch_get_main_queue()) {
self.performSegueWithIdentifier("loginSuccess", sender: self)
}
} else {
self.activityIND.stopAnimating()
if let message: AnyObject = error!.userInfo!["error"] {
self.message.text = "\(message)"
}
}
}
}
is there an error within it?

Answer 1

All your code that manipulates UI objects absolutely, positively must be done from the main thread. (and so it should be in a call to dispatch_async(dispatch_get_main_queue()) as #JAL says in his comment.
That includes not just the self.activityIND.stopAnimating() line, but the code that sets label text as well (any code that manipulates a UIKit object like a UIView).
Your if...else clause should look something like this:
if user != nil
{
dispatch_async(dispatch_get_main_queue())
{
self.activityIND.stopAnimating()
self.performSegueWithIdentifier("loginSuccess", sender: self)
}
}
else
{
dispatch_async(dispatch_get_main_queue())
{
self.activityIND.stopAnimating()
if let message: AnyObject = error!.userInfo!["error"]
{
self.message.text = "\(message)"
}
}
}

Answer 2

So it turns out, in my viewDidLoad() I had the following code in attempt to hide the indicator on the load:
UIActivityIndicator.appearance().hidden = true
UIActivityIndicatorView.appearance().hidesWhenStopped = true
not knowing this would deallocate the indicator for the remainder of the application so when i called the following in my login logic:
activityIND.hidden = false
activityIND.startAnimating()
i was sending a message to an instance that was no longer available, causing the crashes. So all i did was adjust my code in viewDidLoad()
to :
activityIND.hidden = true
activityIND.hidesWhenStopped = true
using the name of the specific outlet I created rather than the general UIActivityIndicatorView

Answer 3

All UI related operation should execute in Main Thread, i.e., within
dispatch_async(dispatch_get_main_queue(){}
block
#IBAction func Login(sender: AnyObject) {
activityIND.hidden = false
activityIND.startAnimating()
var userName = usernameText.text
var passWord = passwordText.text
PFUser.logInWithUsernameInBackground(userName, password: passWord) {
(user, error: NSError?) -> Void in
if user != nil {
dispatch_async(dispatch_get_main_queue()) {
self.performSegueWithIdentifier("loginSuccess", sender: self) //UI task
}
}
else {
dispatch_async(dispatch_get_main_queue())
{
self.activityIND.stopAnimating() //UI task
if let message: AnyObject = error!.userInfo!["error"]
{
self.message.text = "\(message)" //UI task
}
};
}
}
}
Refer some good articles on Concurrency here and here