Let's say the user leaves the phone on the table. (probably on home screen)
A few hours later, he picks it up. And when it does, the iPhone detects the accelerometer, and it rings.
Unfortunately, this is not possible. Once the OS goes to the home screen, applications running in the background have a limited set of options.
Read this article for more information: http://developer.apple.com/library/ios/#DOCUMENTATION/iPhone/Conceptual/iPhoneOSProgrammingGuide/BackgroundExecution/BackgroundExecution.html
Not through officially accepted means (i.e. you could do it on a jailbroken phone conceivably). Primarily, you can't run in the background for that purpose. If the app was running in the foreground, you can easily detect motion and perform an activity - but if the phone is left for too long a period without activity, it will sleep.
Unfortunately, the accelerometer is not one of the specified keys in the UIBackgroundModes option in your apps info.plist.
auido, location and voip are the only ones available for now.
short answer: YES
The trick is to make sure the app doesn't get backgrounded when the phone goes to sleep. The other elements like detecting changes in the accelerometer and playing a sound are all standard features.
As for the no sleep solution, it has been asked before, basically is you play a music sample the app will continue running, so perhaps a loop of silence continuously played.
Only if you left an app designed for that purpose running in the foreground.
It won't be possible if your app is running in the background.
Related
I am using CoreLocation to determine user's location to calculate the distance and show the route on the map. To minimize battery usage I am turning off GPS after getting location and turning it on again after 1 minute. When the application is active everything works fine, but after sending it to background and turning off GPS, the app seems to be inactive at all, it doesn't output anything (using NSLog()). I have added directive to info.plist file to allow the application to run in background. When I don't turn off the GPS in background the app works as well as in foreground.
So my question is the following: does GPS always need to be turned on in background to prevent the application to be suspended or there is another workaround (because the turned GPS drains the battery)?
P.S. I am new to iOS and mobile development at all, so maybe there are some tips that I have to know.
See http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html
Apple does not support long running background task in general.
This does only work for specific tasks:
audio,
location,
voip,
newsstand-content,
external-accessory,
bluetooth-central and
bluetooth-peripheral
When you do not use any of that, your app could be suspended.
In your case ypu have specified location, but disabled the location update. Then for apple there is no reason to keep your app in background mode.
I have read a number of posts here that it is possible to get location updates while the application is in the background.
My question is what to what extent can I do computing in the background and would I handle it as I would any other code, i.e. just a method call, etc.
Thanks a lot.
It is possible, yes. You set the 'location' UIBackgroundModes flag in your Info.plist and then call the Location Manager.
See App States and Multitasking
You can do computing while your application is running in the background, although you run the risk of running down the device battery. It's better to just respond to location events.
The Apple documentation is pretty clear about what your app can do while in the background. You cannot do whatever you want while your app is in the background -- there are only a few things you can do (i.e. play audio, track a users location, etc).
Check out Background Execution and Multitasking.
I'm thinking the answer to this is no, but does anyone know if a Bluetooth connection can be maintained in the background with iOS? I'm thinking I might be able to keep it around with the finite-task background API, but I haven't found anything indicating whether that's true or not. Another option would be to use GPS notifications and just reconnect every time the app gets a location changed notification.
You a right. It's a NO.
But if you use location change notification to wake up your app, you may have a short period of time to use Bluetooth.
I think that the Bluetooth connection should be maintained, but if your bluetooth application is not the foreground application it will not receive any data / commands, when it becomes foreground it will.
It is possible, I use this trick to allow an App to use foreground APIs for iBeacons to allow the app to range even when the App is in the background.
To range for iBeacons it uses a high power API and as so this is restricted to only run when the App is in the foreground and stops all delegates being called once the App enters the background.
By playing a silent audio file and adding the AirPlay capability to your plist it allows your app to run in the background just as it would if it was in the foreground.
I'm not sure if it will work for your case but as iBeacons do use the Core Bluetooth and Core Location frameworks it might just do what you are asking.
http://yifan.lu/2013/12/17/unlimited-backgrounding-on-ios/
Note although this trick has not been patched by Apple in iOS8 beta 5 it is possible they will in an update.
If you're using iBeacons, there are built-in APIs for handling when you enter/exit a beacon region, and you typically get ~5 seconds to range for beacons at that point before the app is put to sleep. Theoretically, you could start a background task w/ expiration handler that might allow you to range for ~30 seconds while backgrounded, but I have not verified this is the case. I do know that the background task can be started when normal CLRegions are entered/exited while in the background, and there is functionally no difference between CLRegions and CLBeaconRegions in terms of region monitoring, so if I had to guess I would say this is more-than-likely possible.
Ever since the first beta came out I’ve been trying to find out if “real” multitasking is possible — i.e. can you put a program in the background and have it hang on to a network connection indefinitely?
I’m thinking about IM or IRC apps, for example. I’ve compiled an app myself on iOS 4, and without changing a thing it appeared to stay running in the background, but for all I know it was just suspended to memory.
The docs say the best you can do is request up to 10 minutes, but in the developer presentation they showed off Skype sitting in the background and then notifying the user that a call was coming in. Does anyone know for sure how this all works?
It appears the answer is no. The API for Skype is a very special case, called the "voip" mode, and requires special behavior, such as marking the socket in use for VoIP.
You can receive alarm notifications in the background (such as time passed). The amount of time you are in the background running state is severely limited by the OS.
Android's background model is complete and in many ways much nicer.
Apple has a guide named "Supporting Multitasking In Your Applications" which you should be able to locate.
Apple's iOS 4 developer docs outline this all very clearly.
When your app is closed or switched away from, it is almost immediately "suspended", meaning the OS freezes the app's state. When the user switches back to your app, your code keeps running just where it kept off. You don't need to add any code to your app to do this, just compile it against OS 4.
The above is true in most cases. There are two reasons the "suspended" model may not apply:
1) If the device starts to run low on memory, the OS will start terminating suspended apps that haven't been switched to in a while, without warning. This is why it's in your best interest for your app to remember it's state as well, so if your app is terminated, then re-opened, the user doesn't really notice because it still returns to right where they left off.
2) Your app uses one of the "background" APIs. These are for audio playback, VoIP services, or location services. In this case, your app is allowed to continue running in the background but only has access to those APIs. Additionally, your app can designate certain long-running tasks as "background tasks" that need to be completed before the app is suspended or terminated, like uploading pictures to Flickr or rendering a video, etc.
The "background task" method doesn't cover pinging servers indefinitely, as there is a time limit for the task, after which it will be forcibly halted. Apps that need that sort of functionality are expected to implement push notifications, just as before.
That should clear this up. All in all I think it's a pretty elegant solution to multitasking on a mobile device.
iOS 4 applications can either be running or suspended. The operating system will try to keep as many requested applications as possible in memory, while all other applications are suspended.
Applications that run in the background can access features such as navigation, audio, and VOIP (but NOT instant messaging). So it looks like you might be out of luck.
-- PC World Multitasking on Apples iPhone 4
It is possible for apps to request background time. Read the docs. I would say it iOS is "controlled multitasking".
You can create a long running background task, I believe these can include networking features. Just have to set the background task flag on the work block.
https://developer.apple.com/iphone/library/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/BackgroundExecution/BackgroundExecution.html
the OS can limit exactly how much time you get though... it will tell you when your time is up giving you a chance to cleanup nicely.
iOS 4 has "real" multitasking to some extend. There are two things to consider:
The UI event loop is single tasking. So only the front app executes on the UI event loop. Not a big deal: detach your main code form the UI event loop (maybe you need to redesign your app).
The OS "may" terminate your app if some criteria are met (e.g. low memory).
Currently one of these criteria is that execution time is limited to 10 minutes (real time not cpu time). However I expect this to change and see better criteria for background app termination (I hope to).
Apart from this you can have timers (event loops) in background.
There is no real multitasking in iOS 4.2 even. because apps will only be allowed to finish the task related to states..for small interval of time and then it will be in suspended state.. If you will set background task for long interval of time then... it will behave unexpectedly like no method will be called when you will try to run the app from anywhere..
You may be interested in this blog post that outlines how "multitasking" works in systems such as iPhone OS 4 and Android.
in fact u can do this, although it's not allowed by Apple. u gotta set up a toolchain in ur mac and use some unofficial SDK...
check http://code.google.com/p/iphone-backgrounder/ for more information
You should use the Push Notifications framework for the feature set you are creating!
I want to use accelerometer of iPhone to get the log file of accelerometer value (maybe for 24 hours). Is it possible to let accelerometer runs in background while other applications are running?
You can do it now, if your app is allowed to run in the background for other reasons. See the Core Motion API's startAccelerometerUpdatesToQueue:withHandler: method here.
Nope, it is not. You basically can't run anything but a music app in the background.
You can run the accelerometer while the phone is suspended though.
See this blog for how to do it: http://marcopeluso.com/2009/08/23/how-to-prevent-iphone-from-deep-sleeping/
I use this technique in my GPS recording app.
No, it is presently not possible, at least if you want to distribute your application through the App Store.