4 whats-new-in-ios7-m4-multitasking-slides

What’s new in iOS7
Networking and Multi-tasking
Jon Flanders
@jonflanders

Tuesday, September 3, 13

What you will learn...


What you will learn...
§ All about the new options for multi-tasking and background execution


Background Tasks


Background Tasks
§ Ever since iOS4, apps could request extra time to execute after being sent
to the background


Background Tasks
to the background
o

15 minutes of execution time


Background Tasks
to the background
o


§ This API remains in iOS7, but you may not need to use it (more on this
later)


Background Tasks
to the background
o


later)
§ If you do use it, the execution semantics have changed


Background Tasks
to the background
o


later)
o

If user locked screen in iOS6, the background task would keep the phone awake


Background Tasks
to the background
o


later)
o
o

iOS7 puts the app to sleep; the app will get a time-slice once the phone wakes up


Background Tasks
to the background
o


later)
o
o
o

iOS7 puts the app to sleep; the app will get a time-slice once the phone wakes up
Execution time not guaranteed to be contiguous


New App Switcher


New App Switcher
§ One of the major changes in the OS


New App Switcher
§ User can swipe up on app snapshot to kill the app


New App Switcher
§ User can swipe up on app snapshot to kill the app
o

Unlike in iOS6, this also kills background execution


New APIs


New APIs
§ Background Fetch


New APIs
§ Remote Notifications


New APIs
§ Remote Notifications
§ Background Transfer Service


Background Fetch


Background Fetch
§ When an app opens, typically it shows fresh data


Background Fetch
§ When an app is brought to the foreground after being in the background,
generally the first thing most apps do is refresh their data


Background Fetch
o

But update happens after the user is already in the app, so the user sees a transition


Background Fetch
o


§ Background Fetch enables an app to update its data in the background


Background Fetch
o


o

If an app is in the background, it will be assigned a time-slice


Background Fetch
o


o
o

If an app isn’t running, it will be started in the background and then assigned a timeslice


Background Fetch
o


o
o

o

If an app isn’t running, it will be started in the background and then assigned a timeslice
When and how often the app is assigned a time-slice is controlled by the OS


Background Fetch API


§ Set the UIBackgroundModes value in the Info.plist to “fetch”


o

This can also be set this via the new Capabilities page in Xcode


o


§ Set the background fetch interval range on your Application object


o


o

No repeating interval


o


o
o

Time-slice assignment is managed by the OS, the range is set by the developer


o


o
o


§ New delegate callback


o


o
o


o

performFetchWithCompletionHandler


o


o
o


o
o

Do your work: call the completion handler when you are done


o


o
o


o
o
o

After the completion handler is called, if you have new data, it will create a new
snapshot of your app


o


o
o


o
o
o


§ Update UI for App Switcher


o


o
o


o
o
o


§ You can test this via debug properties


o


o
o


o
o
o


§ You can test this via debug properties
o

Also on Debug menu


Remote Notifications


§ Since iOS4, notifications could be sent through Apple’s Push Notification
Service (APNS)


Service (APNS)
§ Often sent to notify user of new data


Service (APNS)
o

User is notified via alert or popup


Service (APNS)
o
o

If the user clicked on UI, the app was either brought to foreground or started


Service (APNS)
o
o
o

Race condition: what if app can’t show new data yet because new data can’t even
start to be retrieved until app is in the foreground


Service (APNS)
o
o
o


§ iOS7 enables you to send a notification with a new flag


Service (APNS)
o
o
o


o

content-available : 1


Service (APNS)
o
o
o


o
o

When set, the app gets executed before the user gets the notification


Service (APNS)
o
o
o


o
o
o

Hopefully you can get that new data before the user clicks the alert to bring the app
to the foreground


Service (APNS)
o
o
o


o
o
o

to the foreground

§ Send content-available:1 without an alert in the payload of the
notification


Service (APNS)
o
o
o


o
o
o

to the foreground

§ Send content-available:1 without an alert in the payload of the
notification
o

This becomes a silent notification and is delivered to the app in the background


Remote Notifications API


§ Set UIBackgroundModes to remote-notification in Info.plist


o

Or use new Capabilities UI in Xcode


o


§ Make sure to set content-available: 1 in the payload


o


§ The application:didReceiveRemoteNotification:fetchCompletionHandler
is called with a non-null completion handler


o


o

Call the completion handler when you are done


o


o
o

Call the completion handler when you are done
Silent notifications will be rate-limited. APNS does the work to make sure that device
isn’t overloaded – delayed but not rejected


Networking in the Background


§ Before iOS7, you might want to download or upload a resource after the
your app has gone to the background


§ Background Task API would give you a set time-slice


§ Background Task API would give you a set time-slice
o

What if your operation took longer than the time allowed (i.e. a large resource like a
video or image)?


Background Transfer Service (BTS)


§ iOS7 introduces the BTS


§ You can oﬄoad network work to the BTS


§ BTS will ensure that the work gets completed


o

Works even if your app is in the background or even if it is terminated


o
o

If your app wakes up due to background fetch or notification, this is a great API to pair
with it


o
o

with it

§ BTS manages battery life and data


o
o

with it

o

Requests are classified as discretionary or non-discretionary


o
o

with it

o
o

Discretionary requests will only happen when on WI-FI


o
o

with it

o
o
o

Requests from the background are automatically discretionary


o
o

with it

o
o
o
o

Requests from the background are automatically discretionary
Requests from the foreground can request to be discretionary


NSURLSession


NSURLSession
§ New object in iOS7


NSURLSession
§ Subsumes the functionality of NSURLConnection


NSURLSession
o

API is similar to NSURLConnection


NSURLSession
o


§ Adds more functionality than NSURLConnection


NSURLSession
o


o

Instance storage of credentials, cookies, and other state (vs. NSURLConnection’s global
shared state).


NSURLSession
o


o

shared state).

§ If your app goes to the background or even is terminated after you make
a NSURLSession request, BTS service will still complete the request


NSURLSession
o


o

shared state).

§ If your app goes to the background or even is terminated after you make
a NSURLSession request, BTS service will still complete the request
o

Your app is started or woken up when request is finished and you have a chance to
process


NSURLSession API


NSURLSession API
§ To create an NSURLSession, you need an NSURLSessionConfiguration
object


NSURLSession API
object
o

Configuration object determines foreground/background execution, whether the
request will use only wi-fi, etc.


NSURLSession API
object
o

o

Background configuration gets an identifier (string) to use later to retrieve from BTS


NSURLSession API
object
o

o


§ Implement to appropriate protocols


NSURLSession API
object
o

o


o

NSURLSessionDelegate for high-level events


NSURLSession API
object
o

o


o
o

NSURLSessionTaskDelegate for data-level events


NSURLSession API
object
o

o


o
o


§ NSURLSessionTask really replaces NSURLConnection


NSURLSession API
object
o

o


o
o


o

[resume] method to start task


NSURLSession API
object
o

o


o
o


o
o

[cancel],[suspend],[resume] control methods


NSURLSession API
object
o

o


o
o


o
o
o

Multiple sub-classes for diﬀerent functions


NSURLSession API
object
o

o


o
o


o
o
o


§ NSURLSession also has block-based convenience methods as well


NSURLSession API
object
o

o


o
o


o
o
o


§ NSURLSession also has block-based convenience methods as well
o

Still need to call [resume] on task to kick oﬀ connection


Background Considerations


§ Limited time


§ Limited time
o

You still only get a limited time to execute in the background (less than 1 minute)


§ Limited time
o
o

Make sure to call the completion handlers ALWAYS in less than 1 minute


§ Limited time
o
o
o

Use BTS to enhance the work you can do when called in the background


§ Limited time
o
o
o


§ User control


§ Limited time
o
o
o


§ User control
o

User can turn oﬀ or limit background fetch


§ Limited time
o
o
o


§ User control
o


§ Data Protection


§ Limited time
o
o
o


§ User control
o


o

If you use the recommended levels of data protection, you won’t be able to access
files, keychain, or sqlite DBs when running in the background


§ Limited time
o
o
o


§ User control
o


o

o

If you use the recommended levels of data protection, you won’t be able to access
files, keychain, or sqlite DBs when running in the background
If you need credentials in the background, to lower risk, consider a token that expires
in a short amount of time


Summary


Summary
§ The new background execution features help your app seem to the user
to be running all the time


Summary
§ The new background execution features help your app seem to the user
to be running all the time
§ The new NSURLSession and BTS make foreground networking code
simpler and background networking code possible


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