NSTimer with drawing barChart in Background

Question

I'm using an NSTimer in an iOS App in background, which is saving some data every 30 seconds in an array. The app shows the last 10 values (values of 5 minutes) in a linechart.

My problem is to use the function of saving data into the array every 30 seconds also in background, when the app isn't on screen. I've written a lot of themes about this, but I don't understand it.

My timer is the following:

timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: (#selector(ViewController.counting)), userInfo: nil, repeats: true)
func counting() {
 timerCounter += 1 //Int
 if timerCounter%30==0 {
   arrayOfValues.append(...) //Appending the array
   reloadLineChart() // reload chart
 }
}

Could anyone show me how to solve this? I know, there must be something with the background-methods in the ViewController, but don't now what to type in. I think there must be a function, which is counting in background and a function that is reloading the chart when I'm back in the app.

score 1 · Answer 1 · answered May 23 '16 at 08:24

1

I might understand that you don't want to declare the counter in app delegate, for whatever reason you might have,although I would recommend it. However you can call the functions I mentioned, from the same class in which you have defined the counter. You would need to call it like this:

 override func viewDidLoad() {
    super.viewDidLoad()

    NSNotificationCenter.defaultCenter().addObserver(
        self,
        selector: "applicationWillResignActive:",
        name: UIApplicationWillResignActiveNotification,
        object: nil)
}

func applicationWillResignActive(notification: NSNotification) {
    // stop your counter
}

Then do the same with the other function. Hope is clear.

answered May 23 '16 at 08:24

Alex Zanfir

573
4
13

Hello. This function works, thank you very much. Now I've two observer-functions for resignActive and enterForeground, thats good. But my last question isn't clear. I have this Timer in my app. How can I say the code, that he has to run also in background and write data in the array? – Hemmelig May 23 '16 at 08:41
Addition: Yes I know, there is a better way, but I'm still learning and for this moment, that is better. I will search for the better way, when I understand the MVC-Concept in iOS-Apps even better. – Hemmelig May 23 '16 at 08:42
you have several ways... I would recommend you to follow this example:http://stackoverflow.com/questions/28313702/trying-to-implement-beginbackgroundtaskwithexpirationhandler-and-uilocalnotifica I would also add that iOS will only allow your function to run in the background for 10 minutes. – Alex Zanfir May 23 '16 at 09:29
Thanks for your response! I've tried that and it's running in background, very nice! :) But there is still one problem: Every time, I'm reopening the app, there is one more timer in it. After 5 starts, there are six more seconds per second in the counter-value. because there aren’t enough characters left, I’m using pastebin for my problem: http://pastebin.com/P33WuAFM I hope it is understandable. Thank you! :) – Hemmelig May 23 '16 at 10:25
Addition: I think the problem is, that my timer in the App is reloading after going into the app, and the timer in the background doesn't stop, thats why I have more than one timer. But how to solve that problem? It's very hard to understand for my, thanks for every person who is helping! – Hemmelig May 23 '16 at 10:30
Is there someone who knows a solution for this special problem? :) – Hemmelig May 25 '16 at 11:48

score 0 · Answer 2 · answered May 23 '16 at 07:59

In your app delegate you can use this method :

func applicationWillResignActive(application: UIApplication) {}

The code you add in this function will run right before your app goes in the background . Therefore you can write there the code to stop the counter.

Afterwards you need to use the following function to activate the counter again:

 func applicationWillEnterForeground(application: UIApplication) {}

The code you write in this function will run when you come back to the app again. Hope it is clear enough.

Thank you very much. That is clear. :) But my problem is, that I want to access methods from my ViewControllerClass in AppDelegate, because the Timer is defined there. — Hemmelig, May 23 '16 at 08:14

NSTimer with drawing barChart in Background

2 Answers2