Iphone app is delayed for 10 -15 minutes when iphone is in sleep mode.

Question

Hello Experts!

I have created an app that uses NSTimer, which gets triggered each second.

My problem is that if the Iphone is in sleep mode i get a delay for 10 to 15 minutes before the event is triggered. I have stackoverflowed and googled this and the reason for this seems to be that the phone stops listening for certain events when in sleep mode.

Some people have solved this issue by playing a mute sound, not allowing the phone to sleep.

1. What could be the reason for the delay?
2. The mute sound solution seems to be a very "dirty" one. Is there some other way to solve this?

3. If I use the mute sound solution will it the pass the apple review?

   Code:

   timer = [NSTimer timerWithTimeInterval:1.0f target:self selector:@selector(goAction)userInfo:nil repeats:YES];

   [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
   

   -(void)goAction { Here i check for some dates and then call the activateBeepAlarmView }

Answer 1

Hi Jakob,

What happens in your app when the NSTimer is triggered each second? Please provide code showing the creation of the timer as well as the code for the selector that is called when the timer completes.

Also what do you mean by a "delay for 10 to 15 minutes"? Is the delay always that long or is that how long you wait to awaken the iPhone and then the event is triggered?

Depending on what you need to do every second you can handle this situation in different ways. Please respond and we'll try to work our way through this.

Bart

Answer 2

When the iPhone goes to sleep, so does your app and the runloop that runs the NSTimer.

You seem to think that an NSTimer is some sort of hardware based timer. It is not. It operates completely within the software of the app that launches it. I don't know what is waking your app up but it is definitely not the NSTimer.

In short, what you want to do is impossible. You can't sleep the phone and then have an app still active and running. The mute sound technique is just a kludge to keep the phone awake and the app running.

If you need the phone to stay awake, you need to set the application's idleTimerDisabled to YES. This will prevent the phone from sleeping and the app can remain active. But once you let the phone sleep, it cannot be awaken from app code. Only the hardware can do that in response to an alarm or an incoming message.

Answer 3

Well since no one has answered my three questions I will have to answer them:

1. What could be the reason for the delay? I will have to quote Ben S:

Once applicationWillResignActive gets called on your application you simply stop receiving events: The delegate can implement this method to make adjustments when the application transitions from an active state to an inactive state. When an application is inactive, it is executing but is not dispatching incoming events. This occurs when an overlay window pops up or when the device is locked.

The point of sleep mode is to save energy. To do so, the device stops listening for events like the ones you're asking for. NSTimer events will still fire since they don't require expensive (battery-wise) hardware monitoring. Also, alarms are implemented using NSTimer, so they need to be able to function even when in sleep. Otherwise, people might not wake up and blame their iPhone.

2. The mute sound solution seems to be a very "dirty" one. Is there some other way to solve this?
No, currently I haven't found another solution, please feel free to correct me if I'm wrong. Check out this blog post how to do it.

3. If I use the mute sound solution will it the pass the apple review? Yes

Answer 4

@Jakob,

This is impossible with the "Official SDK". If you're developing apps for jail broken phone, then you can use IOKit framework for this. For more info please refer this.