Post on 01-Nov-2014
description
Multitasking in iOS 7
Mickaël Rémond <mremond@boxcar.io>
Universal Push Notification Platform
Pre-iOS 7 options for background modes
Universal Push Notification Platform
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)
Universal Push Notification Platform
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
Change in background tasks handling (2/3)
Universal Push Notification Platform
// 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"); } } } !
Change in background tasks handling (3/3)
Universal Push Notification Platform
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
Universal Push Notification Platform
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
Universal Push Notification Platform
Two new modes available: !
fetch (App downloads content from the network) remote-notification (App download content in response to push notifications)
Background fetching: close control
Universal Push Notification Platform
!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
Universal Push Notification Platform
Preferences -> General -> Background App Refresh
Background fetching: usage patterns
Universal Push Notification Platform
WWDC 204
Background fetching: App Delegate
Universal Push Notification Platform
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
Universal Push Notification Platform
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
Universal Push Notification Platform
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 notifs: Dev and Apple control
Universal Push Notification Platform
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
Universal Push Notification Platform
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
Universal Push Notification Platform
!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: Usage
Universal Push Notification Platform
!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
Universal Push Notification Platform
!Download / upload tasks in background !Discretionary setting to save battery !Limit download to Wifi only
Background transfers: Tips
Universal Push Notification Platform
!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
Universal Push Notification Platform
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.