ITCamp 2012 - Radu Vunvulea - Building metro style applications on Windows 8 using background tasks

Building metro style
applications on Windows 8
using background task
Radu Vunvulea
iQuest
http://vunvulearadu.blogspot.com
Twitter: @RaduVunvulea

@ itcampro # itcamp12 Premium conference on Microsoft technologies

ITCamp 2012 sponsors Mobile &
Development


Agenda Mobile &
Development

• Why we need background tasks
• Base concepts
• When to use them
• Triggers
• Conditions
• Notifications
• Demo
• Tips and Tricks
• Q&A


Why we need background tasks Mobile &
Development

• What happens with classic applications?

• Where Windows Services vanish?

• Why do I need background tasks?


Windows Metro Applications Mobile &
Development

• Similar to Windows Phone applications
• Only threads from the current application
(foreground) are running


Background tasks Mobile &
Development

• Running code in background
• The background task doesn’t depend on
application state
• Small work items
• No interaction with UI
• What we gain:
– Smooth user experience
– Long battery life


Background task types Mobile &
Development

• System
– Playback manager
– Push notification
– Background transfer API
• Upload files
• Download files
• User-defined
– Almost any type of custom action


When to use them Mobile &
Development

• Receive chat message
• Process an incoming SMS
• Download email
• Display a toast notification
• Execute action when something changes
• Display UI, play music
• Process photos
• Index data


Background task triggers Mobile &
Development

ControlChannelTrigger ServicingComplete
InternetAvailable SessionConnected
InternetNotAvailable SessionDisconnected
LockScreenApplicationAdded SessionStart
LockScreenApplicationRemoved SmsReceived
MaintenanceTrigger TimeTrigger
NetworkNotificationChannelReset TimeZoneChange
NetworkStateChange UserAway
OnlineIdConnectedStateChange UserPresent
PushNotificationTrigger


Background task triggers Mobile &
Development

• Some triggers require the application to be on the lock screen

ControlChannelTrigger ServicingComplete
InternetAvailable SessionConnected
InternetNotAvailable SessionDisconnected
LockScreenApplicationAdded SessionStart
LockScreenApplicationRemoved SmsReceived
MaintenanceTrigger TimeTrigger
NetworkNotificationChannelReset TimeZoneChange
NetworkStateChange UserAway
OnlineIdConnectedStateChange UserPresent

• An application can register to be notified when it is added or removed
from lock screen


Background task conditions Mobile &
Development

• 0..n conditions can be added to each
background task
• Only when all conditions are met, the given
task is launched
Background task condition The condition that must be satisfied
InternetAvailable The Internet must be available.
InternetNotAvailable The Internet must be unavailable.
SessionConnected The session must be connected.
SessionDisconnected The session must be disconnected.
UserNotPresent The user must be away.
UserPresent The user must be present.


Background task infrastructure Mobile &
Development

Application System

4. Launch background task

System

My Application 3. Fire trigger
2. Register class with triggers

Control Channel
Control Channel
1. Register trigger Trigger
Trigger


Where a background task run Mobile &
Development

Application BackgroundTaskHost.exe

Application or
BackgroundTaskHost.exe


Where a background task run Mobile &
Development

TimeTrigger
SystemTrigger
ControlChannelTrigger MaintenanceTrigger

Application BackgroundTaskHost.exe

Application or
BackgroundTaskHost.exe



Notifications Mobile &
Development

• The following notification can send to the
base application:
– Progress notifications
– Completion notifications
– Exceptions thrown
• A background task can be receive
cancellations notifications only from
operating system
– The task have 5s to save his state until the system
close the application


Basic steps to implement Mobile &
Development

• JavaScript
– Add a new dedicated worker file
• C#/C++
– Add a new Windows 8 Metro style app class library project to
the solution.
– Add a reference to the newly added class library project in the
main Windows 8 Metro style app project that registers the
background tasks.
– Ensure that the output type of the class library is Winmd and
not DLL.
– Add the required manifest entries for background tasks to the
Windows 8 Metro style app
– Seal the class that implements the IBackgroundTask


Base classes Mobile &
Development

• IBackgroundTask – used to implement the
background task
• IBackgroundTaskInstance – provides access to a
background task instance
• BackgroundTaskDeferral – used for async calls
from background task
• BackgroundTaskBuilder – used to register a
background task
• BackgroundTaskRegistration – a background
class that was registered
• BackgroundTaskRegistration.AllTasks – get a list
of tasks of the current application


Live demo Mobile &
Development


CPU resource constrains Mobile &
Development

• Limited CPU time for each application
• Use BackgroundTaskDeferral for async calls
CPU resource quota Refresh period

Lock screen app 2 CPU seconds 15 minutes

Non-lock screen app 1 CPU second 2 hours

• Restrictions are applied on AC power also
• Exceptions:
– Control channel
– Push notifications


Network resource constraints Mobile &
Development

• Different network interfaces require different
amount of energy
• Wi-Fi resource constraints:
Average Data throughput, in megabytes (MB) Data throughput, in MB, for non-lock
throughput for lock screen apps screen apps

Every 15” Per day Every 2 hours Per day
1 Mbps 0.1875 18 0.25 3
10 Mbps 1.875 180 2.5 30
20 Mbps 3.75 360 5 60

• On AC power there is no limitation for Wi-Fi
network


Tips and tricks Mobile &
Development

• TimeTrigger minimum time interval is 15 minutes
• Progress and Complete handlers needs to be
associated each time when application start
• BackgroundTaskDeferral can be used for async calls
• Don’t rely on global pool when all allocated CPU
time was used
• When a background task is suspended a message is
logged in the Event Viewer.
• Share data between application and background
task only by files or State Manager


Best practices Mobile &
Development

• Design background tasks to be short lived
• Use persistent storage to share data
between the background task and the app
• Verify if the app needs to be on the lock
screen
• Do not display UI other than toast, tiles or
badges from a background task.
• Do not rely on user interaction in
background tasks

THE END

Radu Vunvulea
iQuest
http://vunvulearadu.blogspot.com
Twitter: @RaduVunvulea


ITCamp 2012 - Radu Vunvulea - Building metro style applications on Windows 8 using background tasks

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ITCamp 2012 - Radu Vunvulea - Building metro style applications on Windows 8 using background tasks