I am trying to take advantage of iPhone 4 multitasking feature. I want to run app in background and frequently send http request to send/receive data, is it possible?
Surprisingly, there is actually very little time-slicing going on in the "multi-tasking" iOS 4.x. What goes on instead is really just application suspend / resume. When an application is sent to the background upon the user tapping the home button, it will stop getting execute cycles after a short while (*).
(*) There are a few exceptions. Applications which declare themselves as "VoIP providers", location-based apps, and music apps can get background execute cycles, presumably only though to perform those very specific operations in response to corresponding events (like a "significant change in location" occurring). Some apps apparently try to stretch the rules and find undocumented or not-strongly-documented techniques to continue getting background execute cycles.
And the "requested running time" that Undeadlegion mentioned is limited in duration.
The reality is that on iOS4, applications are not allowed to run continuously in the background.
#Undeadlegion has suggested a plausible way to achieve your goal. To be more clear, take a look at my previous answer to a similar question at SO, iphone - Connecting to server in background
It is possible to request running time while your app is backgrounded.
See Multitasking Developer's Guide
Although, depending on the intent of your http requests, push notifications may be a viable alternative.
This may be necessary because you aren't providing audio, voip, or location services, so your app can't run in the background indefinitely.
Related
I know this question may be a little bit common and over asked but I cannot find any precise information... so :
Is it possible to have some kind of thread running when the app is in background so I can perform basic sync with my webservice ?
App is in background : I mean the user clicked the Home button, or switched to another app
basic sync : photo upload and download with AFNetworking. I know it has method to continue an HTTPRequest while app is in background, but this is not my point.
My goal would be to make some kind of sync manager, reading a list of photos to update created while the user was on the app, and perform those changes.
I know that the manager could be killed by the OS, but since my server uses atomic transfers it is not a problem. I just need a way to relaunch it... Push ?
I think apps like Google Latitude or Mail and those kind of apps uses what I am looking for but I cannot find any relevant details on it. And using iOS5 is not a problem but waiting for iOS6 would not be a solution.
Thank you for your replies !
PS : well I almost forgot. the app is designed for an enterprise program, so maybe rules are different ? I don't think there is any check for in-house deployment so it might lead to new possibilities...
Apple's Mail client has a background daemon which keeps it running but you can't have that with your own applications. Once an app enters a background state, it must halt it's operations. You can request for a little more time when backgrounded to finish off any transfers or writes to disk (see the Executing a Finite-Length Task in the Background section on Apple's Multitasking Guide)
Google Latitude has events generated based on location. This is a special type of backgrounding introduced by Apple for certain types of applications (see Implementing Long-Running Background Tasks section on Apple's Multitasking Guide) but this can't be used for HTTP syncing. It can only be used for audio, location, voip, newstand content, bluetooth and external hardware attachments.
Push doesn't seem like a solution because it only generates an alert. It doesn't trigger any action until the user triggers the opening of the notification.
You'll want to read Tech Note 2277 Networking and Multitasking.
Basically you have a couple of options:
If you can convince Apple that your app is a VoIP app then you can register a VoIP socket and the OS will resume your background app whenever there is activity on that socket.
Your main option though is to register a background task for any outstanding activity that you have to do when your app is put in the background. You typically get 10 minutes to finish up that work.
Mail is a special app with privileges you don't get.
Apps like Latitude typically register themselves for location updates, specifically to be woken up when there are major geo-position changes. Apps that record GPS tracks do similar things.
Found it !
Using Suhail Patel 's link on Apple's Multitasking Guide I added the voip tag to UIBackgroundModes in Info.plist and use setKeepAliveTimeout:handler: method of UIApplication to relaunch it if needed once the app is going to sleep.
I hope this will help a lot of you !
Of course this app won't be allowed to be on the App Store but for in house development this is in my opinion the best way to do so.
Thanks everyone for showing me the right direction !
I have an application that requires location tracking and I think it fits squarely within one of the allowable background models. However, I need to post to a network service when there are significant changes of location. I've seen write-ups that state network access is prohibited in background processing, but I didn't read that in Apple's docs.
Does anyone know if it's kosher (wrt Apple policies) to make occasional and very quick network updates in a background process?
Good point, according to the Apple documentation only the following usages are allowed in background and each service should be registered:
audio—The app plays audible content to the user while in the background. (This content includes streaming audio or video content
using AirPlay.)
location—The app keeps users informed of their location, even while it is running in the background.
voip—The app provides the ability for the user to make phone calls using an Internet connection.
newsstand-content—The app is a Newsstand app that downloads and processes magazine or newspaper content in the background.
external-accessory—The app works with a hardware accessory that needs to deliver updates on a regular schedule through the External
Accessory framework.
bluetooth-central—The app works with a Bluetooth accessory that needs to deliver updates on a regular schedule through the
CoreBluetooth framework.
Other than this services, you can create a Finite-Length Task in the Background that actually give you the possibility to end a network process.
This can be important if your app is performing some important task,
such as writing user data to disk or downloading an important file
from a network server.
Regarding your question, it's not really clear if you can or not can do a quick network connection if you've a location service running in background. I would say YES for a short connection, but not totally sure. Since iOS 4.0 this usage was denied and clear in documentation, now that part has been removed.
Yes if you use background for just quick connection. Apple won't allow you to run in the background as you want.
NO If your app does not fall in the Voip, music or GPS category; then you can't run in background.
more here: Update my app when it is in background
You could use ASIHTTPRequest.
ASIHTTPRequest has a property setShouldContinueWhenAppEntersBackground:. default is NO, you may turn on YES so you have background network process.
Apple documentation seems a bit unclear on the strict policy. There are definitely applications in the app store that make sporadic network calls while running in the background as a location-based application. An example is the Geoloqi application.
I am developing an iphone application and I think that it's business logic requires a service to be always running in background.
The service needed is to get the acceleration of the device and notify or perform a certain action when that acceleration becomes a certain value.
Is that allowable in the Apple policies, or is there any idea about a solution?
What cydia development possibilities to help me ?
Dbramhall left out one important thing:
You can't guarantee that your app won't be killed, the OS can kill apps that are in the background at will if it requires more memory.
So if at all possible i wouldn't rely on making sure it can run its process in the background and before you ask "How can i stop this?". Well you shouldn't I've never tried it myself because i don't know the effects it has on the OS.
Also if you stop it from being killed in the Background, if it is going to be on the app store then it won't pass evaluation process, because it breaks the OS
Well, an application can run in the background and Apple perfectly accepts this however the user will obviously be be able to close the application (or should be able to) via the multi-tasking bar and this will end the application. Period.
Apple will not accept an application that runs constantly regardless of whether the user has is in background state as this drains the battery, heats the device etc. So an application can run in the background so long as the user can quit it when close it from the multi-tasking bar however it cannot continue to run after the user closed it via multi-tasking - if it does continue, Apple will reject the application.
Also, see 2.16 of the Apple Store review guidelines: https://developer.apple.com/appstore/resources/approval/guidelines.html#functionality
The docs don't seem to offer any guarantees - I'm just wondering if anyone's had any experience of uploading a large amount data after a user 'backgrounds' an iPhone app.
E.g., recording some audio or video and uploading it while there's the possibility that the user will start another app. Is is reasonable to expect to be able to be able to upload several MB of data in the background, perhaps using the VOPI UIBackgroundMode, which should keep sockets active?
First, uploading anything that is not VoIP data in a VoIP background mode violates Apple's guidelines and will probably get your app rejected. But you still have the option of using the normal background task completion API that gives your app another 10 minutes (at the moment, the amount might change in a future release) to finish a task like an upload.
If a foreground app uses a large amount of bandwidth, it is likely that the OS will give it priority over the background task.
Of course, you cannot rely on your upload being finished. If you run out of time, the system will notify you and you should try to resume the upload when the user reactivates your app. But you can't rely on a stable internet connection anyway, even if your app is in the foreground, so I don't really see the difference.
NO, this is not possible. i agree that it creates problems when you have a long operation to make but it is defiantly not 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!