I have developed an application. My application takes feedback from users. When network is not available, then that data is saved in local db. But, once the network is available, it will sync automatically with the central database.
But, I have some problem here. If I save database & send my application to background, once the network is available, it has to automatically do this syncing with the central database. How to do that?
I am using Reachability class to check network availability.
At the present time there is no way to have your app "wake up" when the network becomes available. If the user quit your app without a network connection, you cannot do anything until they voluntarily open your app.
However, you can prompt them to do so using UILocalNotification. If your app is being quit and you have some data waiting to be uploaded, you can schedule a notification to fire in 4 hours (or whatever amount of time makes sense).
If the user opens the app before the notification time and you are able to upload the data, you can cancel the notification and no one will ever know it was scheduled.
If the user does not open the app, the notification will appear, and say something like, "You have data on your phone that you have not uploaded in a while. Connect to the Internet and launch MyAwesomeApp to sync your data."
You cannot do it on iPhone. Your app ceases to exist in a few seconds (once the app moves to the background).
I believe its 5 seconds for all apps, 10 mins for some apps that have requested for more background time.
PS: Unless, you mark your app as a navigation or a music app, which can stay on in the background, theoretically, forever. But I doubt if a feedback app can get approved on the appstore with such permissions.
Keep an additional column in your saved database which marks successful uploading of your data to your server. Set this when the data is written, but not yet uploaded. When it's successfully uploaded, clear the value. You can check this value when your app comes to the foreground, and have it upload any data that hasn't had this column cleared. While your app is running, you can set a timer for an appropriate interval to recheck reachability and if successful, attempt an upload. Only clear your flag when the data is successfully written, and make sure your server doesn't try to process a partial upload (think of someone trying to do this on a subway or train, moving in and out of connectivity).
Related
I'm working on a iOS app where the user is fetching a reasonably sized database online, and then working with it offline. The update, and sync is taking around 10-15 minutes due to the memory constraints on the device and the way I'm handling the transactional inserts. All the while I have a dialog view open notifying the user of the progress, and give him the option of cancelling and reverting the changes to the database.
Anyway, today while testing I noticed that the iTunes app was trying to contact as server and do some background work, but threw an error:
itunesstored[68] <Warning>: Could not load download manifest with underlying error:
Error Domain=NSURLErrorDomain Code=-1001 "Cannot connect
to 112.168.198.2" UserInfo=0x1f8d6150
{NSLocalizedDescription=Cannot connect to 112.168.198.2}
This caused a dialog to display on top of the one I was already displaying, notifying the user that iTunes was unable to connect.
Now when I clicked the 'close' button, that somehow also closed my dialog, causing only parts of the actions, to be taken when the user decides to stop the update, to take place. The async update kept on going in the background, while the database tried to revert the changes causing the database to lock up and I needed to kill the process and restart the app and update. By design, that reverts everything if something terrible like this happens.
Now I noticed that I should make some changes in my code to make it harder for the database to lock up like that, and I'm working on that.
But what I want to know is: is it possible to forbid iTunes, or any other process for that matter, to do any work on the UI thread while a certain critical process in your app is taking place?
The behavior of the iTunes dialog cancel button, i.e propagating down into my dialog can't be considered normal or reasonable.
No, this is not possible. Apps should be coded in a way that accounts for these kind of interruptions. For instance, on an iPhone, what happens if a telephone call comes in? It's the apps responsibility to deal with it; the system will let the call come through irrespective of your "critical process".
In general, it sounds like your app isn't designed in the best way. For instance, 10 minutes to parse a database seems extremely long — how many records does this database have? You should be able to import databases with 100,000 records in a couple of seconds on the iPhone.
I have an iPhone application like facebook for iPhone. My application must connect my server and read all message every two hours regularly. I have a thread to read all message but when the application is terminated the thread cannot work. Can the thread run undependently from main delegate or how can I find solution for this problem?
You cannot have your app do stuff in the background. There is an API to finish tasks like uploading a photo but even that will be killed after around 10 minutes.
But the Apple Push Notification Service seems like the most appropriate solution for your problem. Your server notifies the device that there is something new happening and you fetch the actual messages when the user opens the app.
edit: As of iOS 7 Apple implemented a feature where you can schedule running tasks to fetch data in the background. Those tasks are not guaranteed to run at any specific times. See the release notes for iOS 7 and the linked methods below:
Apps that regularly update their content by contacting a server can
register with the system and be launched periodically to retrieve that
content in the background. To register, include the UIBackgroundModes
key with the fetch value in your app’s Info.plist file. Then, when
your app is launched, call the setMinimumBackgroundFetchInterval:
method to determine how often it receives update messages. Finally,
you must also implement the
application:performFetchWithCompletionHandler: method in your app
delegate.
There is no solution.
Apple does not permit applications to run in the background unless they are of a specific type such as location or audio or voip or newstand (your app can continue to run for about 10 minutes after it was active if it uses shouldBeginBackgroundTaskWithExpirationHandler).
There is no workaround, many many other people have wondered how to do the same thing as yourself before, but there is no legitimate way. Your app cannot schedule any sort of periodic call home activity.
The only way your app can run once its gone into a suspended or terminated state is for the user to launch it, either explicitly or in reponse to a local notification or remote push notification.
Is it possible to get a notification (that launches the app) when the network gets available?What I want is my application to update its contents as soon the internet gets available.The only way I can think of is to send a push from the server once is a while (may be once a day)and that tell the user it might be a good idea to get yourself synchronized.
This is currently impossible if your background task scope is limited to that feature. The only way you could do this is if you had some other legitimate reason to become a background app (aka VOIP or GPS) and run reachability checks every X minutes, and then post a UILocalNotification that allows the user optionally open the app (you cannot programmatically open your app yourself).
I'm creating an app which connects to server and sends some text.
If network (both wifi or 3g) is there, it will immediately send the text to server.
But if there is no network, it keeps on polling for server connection every 5 minutes.
All this part is working fine.
But when using iPhone 4 device, i want the app to check for server connection even when app goes into background. So, when app goes to background and when network comes back, it must be able to send the text to server.
How can I achieve it? I've seen some apps where they say that the app will upload photos to server even in background. How will they do it?
I suggest you read this article from Apple carefully, especially the Completing a Finite Length Task in the Background section.
http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/BackgroundExecution/BackgroundExecution.html
Something to clarify:
Once your app is in the background and is frozen by the OS, there would be no way for your app by it self to wake up and re-connect to the internet.
However, according to the article above from Apple, you can call this beginBackgroundTaskWithExpirationHandler method from your app's delegate to apply for additional time when put in the background, which is to say, though your app cannot wake up by it self when in background, it can, when in the background and not frozen, try to apply for additional time to finish its lengthy task.
Hope it helps.
There is a trick that I think flayvr is using.
If you download and use the app, you will see that they require you to enable your location.
And why is that?
because they want like you to do something in the background even when the app is terminated (they creating an album out of your newly captured photos), and how do they do that?
They use the significant location change, where when someone is traveling some significant distance (something like 500m) each app that registered for significant location change will get awaken for a limited amount of time to perform some quick task and will be terminated in a few seconds.
So your app can register to that event also and when the event of significant location change fired you will be able to send the text to server (quickly).
Hope that helps.
Until now you can do that on iOS7 with Background Fetch.
Take a look at this article.
However you only have up to 30s to get the task done.
According to the article above, there's also another solution called Background transfer service.
If more time is required though, then the Background Transfer Service
API can be used
Create a new project in Xcode and you will see there are bunch of new methods auto generated in app delegate file. like applicationDidEnterBackground, applicationWillEnterForeground etc.
read the description you have to call your thread to upload data on server here.
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