I'm currently writing an application which depends on location tracking and sending data about the position to the server. The problem, however, is that it has to run 24/7 and currently I'm experiencing random crashes which occur every 2-3 days. What I have done to make the application run constantly in the background is I put a NSTimer in a beginBackgroundTaskWithExpirationHandler method right iside the applicationDidEnterBackground method. The timer executes each minute and stops/starts the location service.
Here is a sample crash log
The code basically looks like this:
UIApplication *app = [UIApplication sharedApplication];
__block UIBackgroundTaskIdentifier bgTaskId = 0;
bgTaskId = [app beginBackgroundTaskWithExpirationHandler:^{
NSTimer *t = [NSTimer scheduledTimerWithTimeInterval: 1 * 60.0 target: self selector: #selector(onTick) userInfo: nil repeats: YES];
[t fire];
if (bgTaskId != UIBackgroundTaskInvalid){
[app endBackgroundTask: bgTaskId];
bgTaskId = UIBackgroundTaskInvalid;
}
}];
I am using GCDAsyncSockets for connection purposes, each call having a timeout of approximately 30 seconds.
I'm really out of ideas, what might be the reason the crashes occur?
Your timer is probably firing off AFTER the task is invalidated (after [UIApplication sharedApplication].backgroundTimeRemaining gets to 0.
The thing is that you can't make the application run constantly in the background. If you want to execute code every once in a while, your only option is going to be using the background location API, setting that your app is using the location background mode in its plist.
You would be getting the CLLocationManagerDelegate callbacks, and you have some time to do some work when those methods are called.
See the Apple documentation regarding background modes: http://developer.apple.com/library/ios/#DOCUMENTATION/iPhone/Conceptual/iPhoneOSProgrammingGuide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html
And the location-awarness manual: http://developer.apple.com/library/ios/#DOCUMENTATION/UserExperience/Conceptual/LocationAwarenessPG/Introduction/Introduction.html#//apple_ref/doc/uid/TP40009497
Related
I need to call a method in every 15 seconds irrespective of any fact, whether it is on any view controller in foreground, whether it is in background or it is killed, I need to call it at all times.
I know I can do the delay task using NSTimer
NSTimer* myTimer = [NSTimer scheduledTimerWithTimeInterval: 15.0 target: self
selector: #selector(callAfterFifteenSeconds:) userInfo: nil repeats: YES];
But, I wanted to know where to implement it so that it could fulfil my condition. I guess I can use it in App Delegate but I need a guidance for this to implement it correctly.
Calling it in App Delegate class is right place but it will not work for following cases.
It will not work if your app is killed from back ground.
It will not in background mode continuously. OS will stop that process after certain period of time.
-If the app is killed, you cannot do anything.
-When the app is in background, the OS may kill that process after certain time interval (I believe it is 15 seconds).
Though you can register for location changes, while the app is in background. In that case, your app will continue to receive location updates (such as for google maps).
-(void)callAfterFifteenSeconds {
//1.) do your work
//2.) If required, you can also choose to skip the next scheduling.
BOOL shouldSchedule = YES;
if (shouldSchedule) {
//3.)
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(15 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
//
[self callAfterFifteenSeconds];
});
}
}
[NSThread sleepForTimeInterval:4.0f];
dispatch_async(dispatch_get_main_queue(),
^{
//write you code if you want fire any method after 4 sec//
}
);
I have a timer running when the device enters the background as I want to keep a check on a small amount of data in my service. I am using the following code in the applicationDidEnterBackground method in app delegate
UIApplication *app = [UIApplication sharedApplication];
//create new uiBackgroundTask
__block UIBackgroundTaskIdentifier bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
[app endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
//and create new timer with async call:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//run function methodRunAfterBackground
NSString *server = [variableStore sharedGlobalData].server;
NSLog(#"%#",server);
if([server isEqual:#"_DEV"]){
arrivalsTimer = [NSTimer scheduledTimerWithTimeInterval:30 target:self selector:#selector(getArrivals) userInfo:nil repeats:YES];
}
else {
arrivalsTimer = [NSTimer scheduledTimerWithTimeInterval:300 target:self selector:#selector(getArrivals) userInfo:nil repeats:YES];
}
[[NSRunLoop currentRunLoop] addTimer:arrivalsTimer forMode:NSDefaultRunLoopMode];
[[NSRunLoop currentRunLoop] run];
});
This works absolutely fine, until the device auto-locks and then the timer stops ticking. Any suggestions on how to stop this from happening? The default live time is 5 minutes so the majority of devices will be locked long before this even ticks once.
Thanks
A couple of observations:
As Mr. H points out, beginBackgroundTaskWithExpirationHandler only gives you 30 seconds (previously 3 minutes) in contemporary iOS versions. So an attempt to fire a timer in five minutes won't work.
You can use [[UIApplication sharedApplication] backgroundTimeRemaining] to inquire as to how much time you have left.
When the device locks, the background tasks continue. You should not see the app terminating. If the user manually terminates the app through the "double tap the home button and swipe up on task switcher screen", that will kill the background tasks, but not simply locking the device.
A few comments on timers:
The code is adding timer to background queue. That's generally not necessary. Just because the app is in a background state, you can still continue to use the main run loop for timers and the like.
So, just call scheduledTimerWithTimeInterval from the main thread and you're done. There's no point in using up a GCD worker thread with a run loop unless absolutely necessary (and even then, I might create my own thread and add a run loop to that).
By the way, if it's absolutely necessary to schedule timer on some background dispatch queue, it's probably easier to use dispatch timer instead. It eliminates the run loop requirement entirely.
BTW, it's not appropriate to use scheduledTimerWithTimeInterval with addTimer. You call scheduledTimerWithTimeInterval to create a timer and add it to the current run loop. You use timerWithTimeInterval and then call addTimer if you want to add it to another run loop.
In my app I need to perform location updates in background. For this purpose I registered my location tracking object as observer like this:
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(start)
name:UIApplicationDidEnterBackgroundNotification
object:nil];
and this is the method that starts updating location:
- (void)start
{
NSInteger downloadsCount = [[SGDataManager sharedInstance] countOfActiveDownloads];
NSInteger uploadsCount = [[SGDataManager sharedInstance] countOfActiveUploads];
if (downloadsCount + uploadsCount > 0)
{
[self.locationManager startUpdatingLocation];
}
}
However location updates never start. But if I change UIApplicationDidEnterBackgroundNotification to UIApplicationWillResignActiveNotification then the location updates work perfectly in background. So how do I make it work for did enter background notification?
I want to note that location updates background mode is enabled for my app
When your application goes in to background it has finite time to finish tasks. After that time the tasks will be suspended.
Try to put your UpdateLocation into a background task, like here:
http://hayageek.com/ios-long-running-background-task/
This example also uses location updates while going into background.
EDIT:
In my opinion it's a CoreLocation bug. It could be something like: startUpdatingLocation method finishes, the background task finishes, but there is still something happening in some other thread that CoreLocation spawned and the app suspends this thread because it goes into background. It's just a guess though.
Either way, here's a workaround: extend your app lifetime in background. Do not end the background task when startUpdatingLocation finishes, let it run for a couple of seconds.
__block UIBackgroundTaskIdentifier back = [application beginBackgroundTaskWithExpirationHandler:^{
[application endBackgroundTask: back];
back = UIBackgroundTaskInvalid;
}];
[manager startUpdatingLocation];
This code will let your app run in background for a couple of minutes. You can create a timer that will suspend it faster if you like
NSTimer* killBackgroundTaskTimer = [NSTimer scheduledTimerWithTimeInterval: 10 target: self
selector: #selector(killBackgroundTask:) userInfo: nil repeats: NO];
-(void) callAfterSixtySecond:(NSTimer*) t
{
[application endBackgroundTask: back];
back = UIBackgroundTaskInvalid;
}
You need to enable project Background Modes capabilities.
Go to project properties >> Capabilities section.
Select Background Modes and click switch to turn ON.
In background mode check Location updates true.
This will enable location updates in background mode.
Hey I am developing an app in which i have to make API call every 30 sec, so i created NSTimer for it.
But when my app goes into background timer stops firing after 3-4 minutes. So it works only 3-4 minutes in background,but not after that. How can i modify my code so that timer would not stop.
Here is some of my code.
- (IBAction)didTapStart:(id)sender {
NSLog(#"hey i m in the timer ..%#",[NSDate date]);
[objTimer invalidate];
objTimer=nil;
UIBackgroundTaskIdentifier bgTask = UIBackgroundTaskInvalid;
UIApplication *app = [UIApplication sharedApplication];
bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
[app endBackgroundTask:bgTask];
}];
objTimer = [NSTimer scheduledTimerWithTimeInterval:30.0 target:self
selector:#selector(methodFromTimer) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:objTimer forMode:UITrackingRunLoopMode];
}
-(void)methodFromTimer{
[LOG debug:#"ViewController.m ::methodFromTimer " Message:[NSString stringWithFormat:#"hey i m from timer ....%#",[NSDate date] ]];
NSLog(#"hey i m from timer ....%#",[NSDate date]);
}
I even changed the code with the following:
[[NSRunLoop mainRunLoop] addTimer:objTimer forMode:NSRunLoopCommonModes];
This didn't work either.
Don't create UIBackgroundTaskIdentifier task as local and make it global as below:
Step -1
Step -2
Step -3
Step -4
As local one loose scope and global one won't ,and I created a demo and ran it for sometime with 1 sec repeating timer ,and worked smooth.
Still if u face issue pls let me know.
I ran again demo and here are logs of it running.
So its working fine and more than 3 minutes. Also that 3 minute logic is right but as uibackgroundtask is initiated so it shouldn't let it kill this task of timer.
Edited Part:-
bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
[app endBackgroundTask:bgTask]; //Remove this line and it will run as long as timer is running and when app is killed then automatically all vairbles and scopes of it are dumped.
}];
Check it and let me know if it works out or not.
Hey I run ur code and I reached the expirationHandler but after released debug point ,the timer was running smooth.
No, don't do background tasks with NSTimer. It will not work as you might expect. You should be making use of background fetch APIs provided by Apple only. You can set the duration at which you want it to be called in that API. Though usually it is not recommended setting duration of the call you would like to make. Take a look at this apple background programming documentation
Also, to get you started quickly, you can follow this Appcoda tutorial
This worked for me, so I'm adding it to StackOverflow for any future answer seekers.
Add the following utility method to be called before you start your timer. When we call AppDelegate.RestartBackgroundTimer() it will ensure that your app will remain active - even if it's in the background or if the screen is locked. However, this will only ensure that for 3 minutes (as you mentioned):
class AppDelegate: UIResponder, UIApplicationDelegate {
static var backgroundTaskIdentifier: UIBackgroundTaskIdentifier? = nil;
static func RestartBackgroundTimer() {
if (AppDelegate.backgroundTaskIdentifier != nil) {
print("RestartBackgroundTimer: Ended existing background task");
UIApplication.sharedApplication().endBackgroundTask(AppDelegate.backgroundTaskIdentifier!);
AppDelegate.backgroundTaskIdentifier = nil;
}
print("RestartBackgroundTimer: Started new background task");
AppDelegate.backgroundTaskIdentifier = UIApplication.sharedApplication().beginBackgroundTaskWithExpirationHandler({
UIApplication.sharedApplication().endBackgroundTask(AppDelegate.backgroundTaskIdentifier!);
AppDelegate.backgroundTaskIdentifier = nil;
})
}
}
Also, when starting your app, ensure the following runs. It will ensure that audio is played even if the app is in the background (and while you're at it, also ensure that your Info.plist contains "Required background modes" and that "App plays audio or streams audio/video using AirPlay" a.k.a. "audio" is in its collection):
import AVFoundation;
// setup audio to not stop in background or when silent
do {
try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback);
try AVAudioSession.sharedInstance().setActive(true);
} catch { }
Now, in the class that needs the timer to run more than 3 minutes (if in the background), you need to play a sound when only 30 seconds remains of background time. This will reset the background time remaining to 3 minutes (just create a "Silent.mp3" with e.g. AudaCity and drag & drop it to your XCode project).
To wrap it all up, do something like this:
import AVFoundation
class MyViewController : UIViewController {
var timer : NSTimer!;
override func viewDidLoad() {
// ensure we get background time & start timer
AppDelegate.RestartBackgroundTimer();
self.timer = NSTimer.scheduledTimerWithTimeInterval(0.25, target: self, selector: #selector(MyViewController.timerInterval), userInfo: nil, repeats: true);
}
func timerInterval() {
var bgTimeRemaining = UIApplication.sharedApplication().backgroundTimeRemaining;
print("Timer... " + NSDateComponentsFormatter().stringFromTimeInterval(bgTimeRemaining)!);
if NSInteger(bgTimeRemaining) < 30 {
// 30 seconds of background time remaining, play silent sound!
do {
var audioPlayer = try AVAudioPlayer(contentsOfURL: NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("Silent", ofType: "mp3")!));
audioPlayer.prepareToPlay();
audioPlayer.play();
} catch { }
}
}
}
It is normal behavior.
After iOS7, you got exactly 3 minutes of background time. Before that there was 10 minutes if i remember correctly. To extend that, your app needs to use some special services like location, audio or bluetooth which will keep it "alive" in the background.
Also, even if you use one of these services the "Background app refresh" setting must be enabled on your device for the app.
See this answer for details or the background execution part of the documentatio.
This question already has answers here:
backgroundTimeRemaining returns (35791394 mins)?
(2 answers)
Closed 9 years ago.
I have just entered into iOS programming and am struggling with many things.
I am trying to implement small piece of code to getting current location and send it to server in the background.
When I call beginBackgroundTaskWithExpirationHandler, I found that backgroundTimeRemaining property returns so big number. Look at the log below the code.
if (self.backgroundTask == UIBackgroundTaskInvalid) {
NSLog(#"***** startBackground work");
UIApplication *app = [UIApplication sharedApplication];
self.backgroundTask = [app beginBackgroundTaskWithExpirationHandler:^{
NSLog(#"Background handler called. Not running background tasks anymore.");
[app endBackgroundTask:self.backgroundTask];
self.backgroundTask = UIBackgroundTaskInvalid;
}];
DebugLog(#"====>backgroundTimeRemaining:%.1f seconds", app.backgroundTimeRemaining);
if (timer == nil) {
timer = [NSTimer scheduledTimerWithTimeInterval:10 * 60
target:self
selector: #selector(timerFired:)
userInfo:nil
repeats:YES];
}
}
Log:
2013-11-29 09:23:14.852 JeeneeLocatorService[1666:70b] <JLSViewController.m:(317)> ====>backgroundTimeRemaining:179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368.0 seconds
It does not look normal and I have read from iOS developer library site iOS allows about 10 minutes even though I call
beginBackgroundTaskWithExpirationHandler to do long time background task.
I am testing with iOS7 simulator in XCode5. Is it true that I can have that much of time for background job. Your answer would be very appreciated.
EDIT:
After getting answer, I move the remaining time display code into the timerFired: method.
- (void)timerFired:(NSTimer *)timer {
DebugLog(#"***** Timer fired *****");
UIApplication *app = [UIApplication sharedApplication];
DebugLog(#"====>backgroundTimeRemaining:%.1f seconds", app.backgroundTimeRemaining);
}
But, it still gives me same time left whenever timerFired: method is called. Does not this work just in simulator?
As your new to ios coding, a little tip:
Hold ALT and click on backgroundTimeRemaining. It tell's you it returns an NSTimeInterval which is a double, so using %f is not the problem.
If you click the bottom blue link of the popup it'll open the docs and you'll see it says that this figure will be very large if the app isn't actually in the background.
So I'm guessing this is your issue, that your app is in the foreground when the NSLog is printed.