Is it possible to put your app in the background, and have a counter that once expires, wakes up the app and have the app does some action? I know it's basic, but I just cant seem to have it work. Where do I put this counter + action? Under app did enter background?
Thanks for the help.
I don't think that this works in general:
You are allowed only to run in the background for specific tasks:
Apple doc tells which tasks that are:
One of that tasks is receiving GPS messages.
As long as you have GPS enabled and your app configured that it uses GPS for background, your app stays alive in the background.
If you disable GPS some time later it will suspend, and not wake up till the user activates it.
So to realize your problem you have to stay active in the background (e.g by reading GPS).
You can start the timer in AppDelegate:applicationDidEnterBackground or similar
If you need more time to shutdown, you explicitly can request for more time, there is one method for that. I dont know what happens if you request more at regulary intervals
Related
Is it possible to call method after n minutes even if application will go to background?
What i should use for this?
You can fire a local notification after a set amount of time. But then you can only handle an event in case the user taps "View" on the dialog. Otherwise you can use one of the background modes (Location, Audio, VoIP) to continue running in the background. Then you have all the freedom you wish except that you probably won't get your app accepted in the app store unless you use your app for the purpose that you describe in your background mode.
I recently got an app rejected twice for polling every n minutes using location background mode (even though I was using the location!).
Good luck
I have noticed that some apps e.g. Skype run in the background.
I would like to have my app run in the background also, waking up every 1 seconds to update some data and then going to sleep again.
How can I do this?
I gather that NSTimer's do not work in the background.
You can't. Voice-over-IP apps get a special exception for this, basically the system manages a network socket for them and wakes them up if there's data. There's no way to do the same with a timer.
By the way, waking your app every second, your battery wouldn't last half a day.
See Executing Code in the Background
You would need to use push notifications to push information to the app (like the Facebook or Skype app). See this documentation from Apple on how to use push notifications.
Not every second though, that would drain the battery. Other than that, there isn't really a way unless you are running a VoIP app.
Is it possible to keep a socket connection alive in background, to be able to push new data and alert users at all times?
The answer to this question is a definitive yes. If you are in the background state, then you can keep a connection open and process messages from a server.
Unfortunately the complexity here is that you don't have a lot of control over the state your application is in:
foreground - The user has tapped your icon and the app is running with the UI visible.
suspended - The user was previously running your app in the foreground, but suspended it by hitting the home button or receiving a call. Basically your app is 'freeze dried' and will remain inactive until it is resumed by the user (starting where it left off) or it is terminated by the OS (see below).
background - The app was previously running in the foreground but has moved to the background state as a result of something the user has done. Normally your app will move to the suspended state in this case, but there are things you can do as the developer to prevent the instant 'freeze dry' and go into the background instead (see below). Your app will also be in the background state if it is woken up for a significant change event.
terminated - Your app has been unloaded from memory and the next time it starts will be from scratch. This is what happens when you double click the home button and then tap the x next to your app icon. It moves the app from the suspended state into the terminated state. This will also happen if the OS decides it needs room for more recently running apps and your app has been suspended for a long time.
So obviously the trick here is how do I stay in the background state as a long as possible. There are a couple of ways to do this:
Beg for more time - You can get up to 10 minutes of additional background processing when your app is closed if you ask for it.
Use UIBackgroundMode - You can declare youself a voip, audio or location app by adding the corresponding UIBackgroundMode value to the pList. There are special requirements for these types of apps which you can check out here.
So these approaches are not without their own problems (getting approved on the store being one of them) and as such I tend to agree with the other answers that using push notifications is probably your best approach for notifying your users. With the notification improvements in iOS5 this is going to be the best user experience going forward.
You can keep a socket connection alive (or do whatever else you want) in the background for about 15 minutes after your app closes. There are also more specialized background processing modes (specifically, audio, voip, and location) which Apple supports if your app fits into one of their supported categories. See here.
If you want to keep sending the user notifications indefinitely, you want to use the Apple Push Notification Service. This allows your app to continue to receive notifications when it's not running, and it conserves resources since there's only one connection to the APN service at a time.
You can definitely alert users with local and push notifications.
And as far as I know, you can keep a connection open only for limited time.
Look here for more details.
I am writing an application that records a users position at regular intervals whilst walking. I am using an NSTimers to schedule "startUpdatingLocation" followed by calling "stopUpdatingLocation" shortly afterwards to save as much battery as possible.
I want the user to be able to start the application and lock the phone thereby putting the application in an inactive state. My question is when this happens my application (when running via Xcode) seems to continue as normal, but I am curious if there are any differences in the way the application runs in this state as apposed to when the application is running as active?
From the docs it only mentions "applicationWillResignActive" with regards to the application passing through that state on its way to the background. I am more interested in how an application behaves when a used locks the UI and puts the phone away, I just want to make sure its going to keep doing what it should be doing or do I need to take extra measures?
When you app hits applicationWillResignActive it can continue to receive location updates if you use the UIBackgroundModes option in your apps info.plist.
Add the location key.
It is important that you do not use a timer in the background as timers will run but hold their "fire" until the app becomes active again. Thus you will only get one read when the user comes back to the app. The GPS location accuracy level is what will drive how much the battery is affected.
In your app description in the App Store, Apples requires:
Continued use of GPS running in the
background can dramatically decrease
battery life.
You app will not be allowed to go live until the above text is in the description for the user to read.
You should definitely be testing this on a device. The simulator doesn't auto-lock, for instance.
applicationWillResignActive is called when the user presses the home button, when another app fires a notification the user accepts (including when a call comes in), and when the device locks.
Look into the multitasking documentation, and what it has to say about background location updates.
My suggestion is that you conserve the user's battery by:
- starting a timer, which when fired, starts location updates (and stops the timer)
- when you get an adequately-accurate position record, stop location updates and restart the timer
- if location updates fail, restart the timer for a longer period. Maybe they're underground.
The most efficient approach is using significant location update service while your application is in the background or the screen is locked on your app. You might get one update every ten minutes or so.
Remember also, the user can disable your app's location services permissions. Especially these days...
I can't seem to find a clear answer to this-- I'm spec'ing out an iPhone app that I'd like to have live in the background and notify the user at certain periods throughout the day. So the user would launch the app in the morning and then continue to use their phone, then every few hours the app would pop open a notification dialog.
Will my app ever be shut down (automatically) by the OS? Or will it just live forever, notifying user when it needs to?
thanks,
Eric
Basically there are three kinds of running in the background on iOS 4:
Running in the background to "finish" stuff (e.g. upload a posting or a picture, finish processing something etc.). You ask the OS to grant you extra time after the user switches to another app, and it will tell you how much time you got. You can't run in the background for an indefinite time.
Running in the background to do specific stuff: VoIP, tracking location (e.g. for GPS navigation), or playing audio. You can only do the stuff that you told the OS you would do in the background.
Local notifications (UILocalNotification). From your description, this is what you're looking for. You're not actually running, you just schedule notifications, and when it's time to notify the user, they'll be notified and can go to your app. If you need to notify the user dynamically (i.e. you don't know ahead at what times they need to be notified and it's not location or VoIP triggered), you might want to look into push notifications.
Apple has a good overview here:
https://developer.apple.com/documentation/uikit/app_and_environment/scenes/preparing_your_ui_to_run_in_the_background/about_the_background_execution_sequence