NSTimer stops after a few seconds

Question

I'm making a social media app and one of the features in the sign up screen is it checks if the username is taken in real time and puts an X or Check if it's taken (again in real time). I use a timer to accomplish this but for some reason the timer stops after a few seconds. What's going on? And is there a better way of going about doing this?

override func viewDidLoad() {
    username.delegate = self
    email.delegate = self
    password.delegate = self
    var timer = NSTimer()
    timer = NSTimer.scheduledTimerWithTimeInterval(0.01, target: self, selector: Selector("checkOrX"), userInfo: nil, repeats: true)
}

func checkOrX() {
    var query = PFQuery(className: "_User")
    query.whereKey("username", equalTo: self.username.text)
    query.findObjectsInBackgroundWithBlock { (users, error) -> Void in
        if let users = users {
            self.usernameCheck.image = UIImage(named: "X.png")
        } else {
            self.usernameCheck.image = UIImage(named: "Check.png")
        }
    }
}

woah, i doubt parse will appreciate that request spam. In what way does the timer "stop"??? Have you added a logging statement? — luk2302, Aug 29 '15 at 16:57
logging statement: `print("in checkOrX")` in the method. Spend some time reading about debugging, you will be doing a lot of it, we all do. — zaph, Aug 29 '15 at 17:01
you did not just seriously ask what I mean with logging :O :'((( — luk2302, Aug 29 '15 at 17:01
It might be more effective to check only if the content of the text field changes – there are notifications for that purpose – rather than 100 times a second. — vadian, Aug 29 '15 at 17:03
@luke2302 Oh I know what a logging statement is. I actually did a lot of that during this. And found out that it stopped printing to the logs. — Ethan Cotler, Aug 29 '15 at 17:03
@vadian How would I use that? Would I implement that in my timer or what? — Ethan Cotler, Aug 29 '15 at 17:09
please read the documentation about text programming: https://developer.apple.com/library/ios/documentation/StringsTextFonts/Conceptual/TextAndWebiPhoneOS/Introduction/Introduction.html section Managing Text Fields and Text Views — vadian, Aug 29 '15 at 17:10

score 5 · Accepted Answer · edited May 23 '17 at 12:29

Instead of sending 100 requests a second which is bad for multiple reasons, you should send a request at most every time the user changes the actual user name.

Why your current solution is bad:

You send too many requests - period
You send the same request most times over and over again
You might get banned from parse for spamming this much
You cause far too much network traffic, assume someone on mobile internet is filling out the login form for 5-10 seconds, getting distracted and having the app open for 1 minute or so, I personally would not be happy to loose a few megabytes for only that.

What you could do:

send the request after every change the user makes to his username (use this question & answer and combine it with your checkOrX)
as soon as you send a new request, cancel previously sent requests that have not finished your current
wait for tiny pauses of the user - if he does not type a new character for 0.1 seconds and only then query the server
only send the request if the user tries to submit the form
only send the request if the user focuses another form element
etc.

An example version of the first "solution" would probably look like

func viewDidLoad() {
    // ...
    self.username.addTarget(self, action: "textFieldDidChange:", forControlEvents: UIControlEvents.EditingChanged)
}

func textFieldDidChange(textField: UITextField) {
    if textField == self.username {
        checkOrX()
    }
}

How would I send a request every time the username is changed? — Ethan Cotler, Aug 29 '15 at 17:12
@EthanCotler I added a little more detail to that particular case — luk2302, Aug 29 '15 at 17:16

NSTimer stops after a few seconds

1 Answers1