I'm building an app that fetches data from a third party server and syncs some of that data to my own server. The data for all users will be aggregated on my server and the results will be displayed in the app. The whole data sync (3rd party server -> App -> My server) should be done at least once a day. The app is only for a limited group of users and will be distributed with an enterprise account.
I'd prefer it to sync the data in the background, so the results on my server are always up to date and do not depend on the single users to open the app. I figured I'd use setMinimumBackgroundFetchInterval with UIApplicationBackgroundFetchIntervalMinimum so the sync would be handled in performFetchWithCompletionHandler in my AppDelegate. Unfortunately it doesn't seem to be possible to set a fixed interval for the background fetch. So I can't control when the sync is done, since it partly depends on the way the app is used when and how often the background fetch is executed.
Is there a way to modify the background fetch so I could guarantee the daily sync?
Or is there any other way to execute a background task on a daily basis with which I could accomplish the above?
The only solution I could come up with is a usability nightmare with daily local notifications to remind the users to open up the app, so that the background fetch can "learn" when to execute. I know this sounds bad, but I do have to present a solution to our customer :/
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We have an iOS app which is collecting some data (location, accelerometer, etc.) in the background. We would like to upload this data to our server so our server can do some analysis on the data; we would like to batch all the collected data and upload it to our servers periodically, perhaps every 12 or so hours (so ~2 times a day).
After looking around I've seen lots of recommendations:
Background Fetch: This appears to be limited to downloads and also isn't guaranteed execution
Silent (Push) Notification: This also appears to be not guaranteed, especially when the app is terminated. Also setting up our server to auth with APNS and send notifications seems excessive for such a simple 'problem'.
Continuing Upload: Specifically when the app is entering the background. This is a good first step, but because we want to batch data doesn't solve the upload on schedule problem.
I was considering testing if we could use applicationSignificantTimeChange to kickoff an upload at midnight, but that seems to only trigger when the app is opened.
So my question is, is it possible to "wake" our app on a schedule to start a background upload?
You can look into the Background fetch again and I believe it can solve your problem.
Look into Selene Library on how to run periodic tasks.
and also glance through how to run code when your app is terminated
Im quite new to iOS programming and now want to implement a periodic background synchronization to synchronize my server data with client data. What I want to achieve is comparable with Androids SyncAdapter where you can define a time interval (for example each 30 minutes) and the system will trigger the defined task automatically in the background.
Until now I could not find such mechanism for Swift 3.0 so I need to ask if somone has experience or some hints for me how I can achieve this.
What I want to do sounds quite simple:
When the app starts for the first time the app should setup a sync manager which automatically triggers a background task every 30 minutes. The background task is responsible to synchronize server and client data (using Alamofire).
How can I do that?
There is an iOS feature called BackgroundFetch, which you can set up for
regularly downloads and processes small amounts of content from the network
You can setup a minimumBackgroundFetchInterval.
In contrast to the mentioned Android feature, this interval is not guaranteed though.
The OS does some heuristic in a blackbox. It rewards you for using a "reasonable" (to the OS) CPU time/ power consumption and also for being used often by the user. On the other hand you get punished for draining the battery or (even worse) never being used/opened by the user.
See: Apple Sample and Apple Docs
Update: Since iOS13, BackgroundFetchis deprecated.
There is a similar, new API named BGTask, BGAppRefreshTask is the equivalent to deprecated BackgroundFetch.
See Apple Docs
Alternatively, depending on your needs, you can post a Silent (push) Notification whenever the users data changes on server side. A silent push wakes up your app without notifying the user, so you can fetch data and maybe inform the user by scheduling a local notification.
See: Apple Documentation
You can't. Apple doesn't allow 3rd party apps to have regular background time like that. You'll need to come up with another approach like implementing a silent push notification from your server when new content is available.
As #ekscrypto points out in their comment, you can use Background fetch to load small amounts of data when the system decides to fetch it. However, you don't have any control over when that fetching takes place. Search on "Fetching Small Amounts of Content Opportunistically" in the Xcode help system for more information.
After working with complications for a few days, I feel confident saying the following about the update process for updates that happen at a prescribed interval:
The system calls requestedUpdateDidBegin()
This is where you can determine if your data has changed. If it hasn't, your app doesn't have to do anything. If your data has changed, you need to call either:
reloadTimelineForComplication if all your data needs to be reset.
extendTimelineForComplication if you only need to add new items to the end of the complication timeline.
Note: the system may actually call requestedUpdateBudgetExhausted() instead of requestedUpdateDidBegin() if you've spent too much of your complication's time budget for the day. This is the reason for this question.
If you called reloadTimelineForComplication, the system will call getCurrentTimelineEntryForComplication (along with the future and past variants that get arrays, depending on your time travel settings)
This is conjecture as I haven't tested it yet, but I believe if you called extendTimelineForComplication that only the getTimelineEntriesForComplication(... afterDate date: NSDate ...) would be called.
The system will then call getNextRequestedUpdateDateWithHandler so you can specify how long until your complication requires a new update.
Apple's documentation is quite clear that you should not ask for updates too often, or conduct too much processing in the complication code or you will exhaust your time budget and your complication will stop updating. So, my question is: where and when do you do the update?
For context, my scenario is a URL with return data that changes up to two times per hour.
The most obvious place in which to put the URL fetch code is func requestedUpdateDidBegin() Fetch the data, store it, and if there's no change, just return. If there was a change then extend or reload the timeline.
However, a URL fetch can be costly. Alternatives:
Put the code on the phone app and send it over with a WCSession, but if the user closes that app then the updates will no longer happen.
Use push updates, but this isn't a web app, so I have no place to send them from.
Obviously I will update all the data when the user interacts with the watch app, but that now means it only gets updated when the user uses the app, which negates the need for a complication.
Is there anywhere else? Can I have a periodic function in the watch app that isn't part of the complication? Where is the right place to fetch the data for a complication update?
For watchOS 3, Apple recommends that you switch from using the complication datasource getNextRequestedUpdateDate scheduled update to update your complication.
The old way for watchOS 2
requestedUpdateDidBegin() is really only designed to update the complication. Keeping your complication (and watch app) up to date usually involves far more than reloading the timeline (and asynchronously retrieving data never fit in well with the old approach).
The new way for watchOS 3
The new and better approach is to use background refresh app tasks. You can use a series of background tasks to schedule and handle your app extension being woken in the background to:
Fetch new data
using WKWatchConnectivityRefreshBackgroundTask to obtain data from the phone, or
using WKURLSessionRefreshBackgroundTask to download data from a server
update your model once the data arrives,
update your complication from the model (by reloading or extending the timeline), and finally
update your app's dock snapshot to show the data on the dock
Call each tasks’s setTaskCompleted method as soon as the task is complete.
Other benefits of using app tasks
One of the key features about this design is that the watch extension can now handle a variety of foreground and background scenarios which cover:
initially loading data when your app/complication starts,
updating data in the background, when the extension is woken by a background task, and
updating data in the foreground, when the user resumes your app from the dock.
Apple recommends that you use each opportunity you are given regardless of whether your app is in the foreground or background to keep your complication, app, and dock snapshot up to date.
Are there any limitations?
The number of total available tasks per day is divided among the number of apps in the dock. The fewer apps in the dock, the more tasks your app could utilize. The more apps in the dock, the fewer you can utilize.
If your complication is active, your app can be woken up at least four times an hour.
If your complication is not active, your app is guaranteed to be woken at least once an hour.
Since your app is now running in the background, you're expected to efficiently and quickly complete your background tasks.
Background tasks are limited by the amount of CPU time and CPU usage allowed them. If you exceed the CPU time (or use more than 10% of the CPU while in the background), the system will terminate your app (resulting in a crash).
For more information
A good introduction explaining when and why to update your watch app is covered in Designing Great Apple Watch Experiences.
For specifics, the Keeping Your Watch App Up to Date session covers everything you need to know to keep your complication, app, and dock snapshot up to date.
WatchBackgroundRefresh sample code demonstrates how to use WKRefreshBackgroundTask to update WatchKit apps in the background.
Edit: El Tea (op) has posted a good answer at https://stackoverflow.com/a/32994055/630614
This is an interesting question/problem, and I've been wondering about a lot of the same!
For the most part, it seems that when I'm working on a new complication I need to step back and see when I really want to update it. A "countdown" complication could set all future timeline entries at one time, when the "end date" is set. An app that shows the current status of a web service could have relevant data stored in NSUserDefaults when an APNS comes through.
If you don't have access to APNS, don't want to run your iOS app in a background mode, and don't want to make HTTP requests from Apple Watch, I can think of 2 other options.
1) Schedule local notifications. The good part is that your Apple Watch should run didReceiveLocalNotification, but the bad part is that the user will get a notification when you're simply trying to check the status without a disruption.
2) Send a message to iOS via sendMessage(_:replyHandler:errorHandler:) in your reloadTimelineForComplication method, setting nil for the replyHandler to make it as quick as possible:
Calling this method from your WatchKit extension while it is active and running wakes up the corresponding iOS app in the background and makes it reachable.
Your iOS app could perform whatever network requests are needed and then store the information or push it to Apple Watch. Unfortunately, I don't think the watch extension will have it's session.didReceive... called until you run it, but you could access the data on the next call to requestedUpdateDidBegin.
As I said, I'm very interested in this same thing, so post some thoughts back and maybe we can extrapolate on some best practices here.
I have an iOS app that needs to sync a lot of data from the cloud to device when first installed, maybe even 2GB worth if the user wants access to everything offline. Without saying "change your design", how can I ensure this initial sync completes without too much interaction from the user?
Currently it will complete as long as they keep my app in the foreground and don't let the device go to sleep. I'd like to allow them to use other apps or let the screen turn off during this process, since it's a pretty boring thing to watch.
I've seen application:performFetchWithCompletionHandler: and
beginBackgroundTaskWithName:expirationHandler, but they only allow for a short amount of time (around 30 seconds) to complete a task. Is there something better, or do I need to complicate my design by stopping my sync every ~25 seconds, and then resume next time I'm given more time by the OS?
My app is like Microsoft Outlook, it has emails (in some case millions), contacts, calendar, and several other areas. I have different sync options to limit the amount of data, but some users want access to everything offline (yes, even emails and attachments that are 10 years old). I think they are silly, but can't argue with the end-users.
I know this is a really old question, but I suggest you use NSURLSession to download data in the background even without your app running.
You simply create an NSURLSession that uses a Background NSURLSessionConfiguration (use NSURLSessionConfiguration.backgroundSessionConfigurationWithIdentifier:) and create an NSURLSessionDownloadTask for each request you need to download.
NSURLSession will download the data even when your app is not running at all, and it will save the data as files in your app's sandbox. Implement the NSURLSession delegate methods to receive notification of the download completion, read the downloaded files and save them how you see fit.
You should check out Apple's guide on Using NSURLSession.
I am working on ios app that used to read ticket data as a barcode scanner. It needs to upload data frequently to a web server, Like two or three times a day. I have done the sync function. I just wanted to run the function when the app is run in background.
This is not possible on iOS, Apple is not allowing any kind of background service on iOS.
The options you are left with is setting your apps background mode to fetch and implement application:performFetchWithCompletionHandler:. But it is totally up to ios if and when this method is called.
You could misuse one of the other background modes to keep your app open in the background, but Apple might reject your app for doing so. Also user might complain about you app draining battery.
What kind of data is that you need that you have to update it two to three times a day? I would say the when the app is opened by the user would be a good time to update, because this is when the user is expecting new data.
If you need to inform the user about some data changes you should be pull it in the app but a server should send a push notification to inform the user that there is new data.