Multitasking in iOS 7

Multitasking in iOS 7

Mickaël Rémond <[email protected]>

Universal Push Notification Platform

mailto:[email protected]

http://boxcar.io/developer

Pre-iOS 7 options for background modes


Previously you had access to the following options: !

Audio playback Location update Task completion (up to 10 minutes) Newsstand download Voice-over-IP (VoIP) services Accessory or CoreBluetooth communication !

Specific limitations for each of them


Change in background tasks handling (1/3)


Apps will get scheduled when device is active and not keep it awake They still get up to 10 minutes run time, not guaranteed to be continuous !

WWDC 204




// AppDelegate UIBackgroundTaskIdentifier background_task; !- (void)applicationDidEnterBackground:(UIApplication *)application { if([[UIDevice currentDevice] respondsToSelector:@selector(isMultitaskingSupported)]) { NSLog(@"Multitasking Supported"); if (background_task == UIBackgroundTaskInvalid) { background_task = [application beginBackgroundTaskWithExpirationHandler:^ { NSLog(@"Background task expiration\n"); //Clean up code. Tell the system that we are done. [application endBackgroundTask: background_task]; background_task = UIBackgroundTaskInvalid; }]; //To make the code block asynchronous dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ //### background task starts NSLog(@"Running in the background\n"); while(TRUE) { NSLog(@"Background time Remaining: %f",[[UIApplication sharedApplication] backgroundTimeRemaining]); [NSThread sleepForTimeInterval:1]; //wait for 1 sec } //#### background task ends //Clean up code. Tell the system that we are done. [application endBackgroundTask: background_task]; background_task = UIBackgroundTaskInvalid; }); } else { NSLog(@"Multitasking Not Supported"); } } } !




On iOS 6, starts with 10 min: 2013-11-14 08:59:54.165 Background1[149:1103] Background time Remaining: 599.981943 !!On iOS 7, starts with 3 min: 2013-11-14 09:02:33.182 Background1[6315:1803] Background time Remaining: 179.942678

!This is a big change for many apps using background tasks. !I never seem task being scheduled discontinously … Yet.


iOS 7 new background modes


With iOS 7 you have three new modes: !

Background fetching Remote notification Background transfers !

All modes keep Apple and users in control to preserve battery life


Project *info.plist: select background modes


Two new modes available: !

fetch (App downloads content from the network) remote-notification (App download content in response to push notifications)


Background fetch



Background fetching: close control


!iOS stays in control: “Application launched opportunistically”

Coalesced across applications means scheduled based on usage pattern sensitive to energy and data usage

!Users stay in control:

Force close disable background fetch Dedicated setting panel


Background fetching: user control


Preferences -> General -> Background App Refresh


Background fetching: usage patterns


WWDC 204


Background fetching: App Delegate


New delegate method on UIApplication is called - (void)application:(UIApplication *)application! performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult! result))completionHandler;!

!Call the completion handler when fetch is complete to let iOS 7 learn about data availability patterns:

UIBackgroundFetchResultNewData!UIBackgroundFetchResultNoData!UIBackgroundFetchResultFailed


Background fetching: Limit server load


At application launch: !Define the minimum fetch interval to limit server load: - (void)setMinimumBackgroundFetchInterval:(NSTimeInterval)minInterval;!

!Use constants: const NSTimeInterval UIApplicationBackgroundFetchIntervalMinimum!const NSTimeInterval UIApplicationBackgroundFetchIntervalNever!

!More likely custom values (in seconds)


Background fetching: Tips


Simulate background fetch for testing Do not forget simulator has an option to manually trigger background fetch

Limit operation to bare minimum You have at most 30 seconds of time to perform download operation

Use NSURLSession to benefit from background download infrastructure Track background fetches per user on your server to discover patterns


Remote notifications



Remote notifs: Dev and Apple control


Developers control: content-available set to 1 in APNS payload to tell the application content is available.

!Apple stays in control:

Silent notification (without sound / alert / badge) can be delayed: Battery saving Normal notifications are send immediately


Remote notifs: App Delegate


New delegate method on UIApplication is called - (void)application:(UIApplication *)application! didReceiveRemoteNotification:(NSDictionary *)userInfo! fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler;!

!Call the completion handler when download is complete to let iOS 7 learn about data availability patterns:

UIBackgroundFetchResultNewData!UIBackgroundFetchResultNoData!UIBackgroundFetchResultFailed!


Remote notifs: Tips


!Limit operation to bare minimum

You have at most 30 seconds of time to perform download operation !

Use NSURLSession to benefit from background download infrastructure


Background transfers



Background transfers: Usage


!Used for data download and upload !Used for granting iOS control over background operation !

Does not obsolete AFNetworking especially if you need parsing / serialization !Quite a large piece of code with many options: Take the time to learn them, they are powerful


Background transfers: Nice features


!Download / upload tasks in background !Discretionary setting to save battery !Limit download to Wifi only


Background transfers: Tips


!Take the time to explore all the options / cases. To implement complex cases, data will flow through multiple paths in code !Not “magic”: You still have to handle network failure and errors, resume on the next chunk

Do not forget there is a server on the back that will timeout at some point !

Take it as a great toolbox to handle advanced cases


References


Talk example code https://github.com/boxcar/talk-code-examples/tree/master/background-ios7 !

Background Modes in iOS Tutorial (pre-iOS 7) http://www.raywenderlich.com/29948/backgrounding-for-ios !

WWDC 2013 Session 204: What’s new with multitasking.


https://github.com/boxcar/talk-code-examples/tree/master/background-ios7

http://www.raywenderlich.com/29948/backgrounding-for-ios

Multitasking in iOS 7

Technology

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