I was recording a sample of CMDeviceMotion acceleration data for 30 seconds through NSTimer. The thing is, when the app is in foreground, everything is fine. The interval is set to 0.01 and in 30 seconds, 3000 readings are stored. But when app goes to background, I get 300 only readings.
self.deviceMotionTimer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:#selector(recordUpdates) userInfo:nil repeats:YES];
Is this how NSTimer works?
NSTimer will never work in background. When your app goes to background, NSTimer also freezes. In short, You can't use NSTimer, when you want to do some repetitive task in background.
If you still want to run something in background, then use the answer given by #Robert in this thread:
Scheduled NSTimer when app is in background?
Related
In my iOS application I am using NSTimer to to record some events happening in my app. Now I want to keep them recording when my app goes to the background so that even if my app is in the background, my NSTimer will continue to record the events.
Can somebody guide me how I can achieve this behaviour?
Unless you enable one of the Background modes, it is not gonna work.
Why?
You have around 10 minutes of background execution after this the timer is stopped by ios.
The timer will not fire after app is locked (iOS7), since ios suspends the foreground app and bgTask will not get fire again.
There is some workarounds, consider to check below
// NSTimer run when app in background
[[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:nil];
loop = [NSTimer scheduledTimerWithTimeInterval:0.25 target:self selector:#selector(Update) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:loop forMode:NSRunLoopCommonModes];
Anotherway check this NSTimer in Background
Timers can not run in background. The only thing you can do is, record the time when application goes into background and when application comes into foreground. Take the difference and do the appropriate action.
I'm using the pitch detection code from demetri miller demetri miller pitch detection in my application. I want the microphone to work in background and give a UILocalNotification on a particular pitch.
How to make the application run in background.
Currently when the app is in background is there way to make it work fully.
Use the NSTimer when app is going from foreground to background start NSTimer and every one second your timer method will call and you can check the application state. you can execute every thing fine.
NSTimer *timerBackground = [NSTimer timerWithTimeInterval:1.0
target:self
selector:#selector(YourMethod:)
userInfo:nil
repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:timerBackground forMode:NSDefaultRunLoopMode];
Scenario is:
Application has on main run loop that runs every 5 min. When app is backgrounded, the timer is not invalidated.
On foreground after waiting a bit (say 10 min), the timer immediately fires twice. I'm unclear as to what the defined behavior here should be (if any) other than on background, the timer is paused/suspended along with the app.
It seems to me that when the app is foregrounded, the timer actually looks at the elapsed time since background, determines the number of times it should have fired in between, and fires them all. I observed this scenario happening both on iOS 7 simulator and iOS 7 iphone.
Google search didn't turn up much info on this topic. Any ideas/pointers?
Update: Clarification - my question is what is the behavior for NSTimer when the application is backgrounded and then foregrounded again, assuming the timer is not invalidated/nil-ed on background, and a new timer is not created on foreground.
Code sample (code is bit old - pre ARC days):
#implementation ReportHandler {
NSTimer *_reportTimer;
}
- (id)init
{
if (_reportTimer == nil) {
_reportTimer = [[NSTimer timerWithTimeInterval:5*60 target:self selector:#selector(didFireReportTimer:) userInfo:nil repeats:YES] retain];
[[NSRunLoop mainRunLoop] addTimer:_reportTimer forMode:NSDefaultRunLoopMode];
}
}
- (void)didFireReportTimer:(NSTimer *)timer {
// send report over network here, timer is not invalidated here
}
There are no background/foreground handlers either here or in the app delegate dealing with this timer.
It seems to me that when the app is foregrounded, the timer actually looks at the elapsed time since background, determines the number of times it should have fired in between, and fires them all. I observed this scenario happening both on iOS 7 simulator and iOS 7 iphone.
That is a correct description of the behavior of NSTimer and the run loop. When your app is suspended it won't fire (by default, when you background it; but if you start a background task, it will fire as normal while the task is running).
Until yesterday I was sure, the NSTimer will get stopped after the app goes into background. I'm have a feeling like experiencing some anomally.
My app has update location and play audio background modes. Update location is refreshed every few seconds. But it only happends on one of the app screens. There also is NSTimer refreshing some UI.
I've scheduled it like this:
[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:#selector(updateTime) userInfo:nil repeats:YES];
There is also a method, which content is irrelevant now:
-(void)updateTime
{
//irrelevant content, but the method gets fired even when the app is in background
}
The weird thing is, thah the method, which is only fired by the NSTimer and nowehere else is fired even after the ap go into the background. What is happening here? Is that normal behaviour?
Because you are using background modes with location and audio your app is still alive in background.and so your timers are running.
If you remove background modes with location and audio that you are using and then try the timers wont work.
Its Normal behaviour. Correct me if i'm wrong.
Create your timer as public i mean add it in .h file and access it when your app. enter in backGround Mode
- (void)applicationDidEnterBackground:(UIApplication *)application
By above method and set your timer as inValidate.. its fix.
And if you want to do again start your timer then you can access it by
- (void)applicationWillEnterForeground:(UIApplication *)application
this method. Here you need to recreate your timer.
You can stop the timer using invalidate the timer.
[self.timer invalidate];
self.timer= nil;
How can I prevent a NSTimer from being delayed by the user scrolling a table?
I found the answer:
I had a timer that repeated about 8 or 9 times with intervals of 0.4 to 0.8 seconds. I don't need much precision, but if the user scrolls a table the timer would stop working until the table finished scrolling (this could be a few seconds wait!). I thought I needed background threads, but timers on background threads were somewhat complicated to implement.
The answer to my problem was very very simple and easy. I just need to add a line after invoking the timer:
//////////// start the timer
self.playingTimer = [NSTimer scheduledTimerWithTimeInterval:tempo target:self selector:#selector(playSoundFromArray:) userInfo:nil repeats:YES];
//////////// the magic line:
[[NSRunLoop currentRunLoop] addTimer:self.playingTimer forMode:UITrackingRunLoopMode];
Now I can scroll the table as much as I want and my timers work OK!!!
Now I need to study a little more NSRunLoop...
You should add your timer for NSDefaultRunLoopMode mode. UITrackingRunLoopMode is used by tracking UI actions(in your case scrolling).