Windows Phone Fast App Switching, Tombstoning and Multitasking

Ben RigaTechnical EvangelistWindows Phone

benriga@microsoft.com@benriga

Follow me on Twitter

or the Puppy gets it@benriga

Topics• Fast Application Switching• The Windows Phone execution model• Application State Management• Fast Application Switching• Dormant programs and Tombstoning• Application Navigation and Application Switching

• Background Tasks• Generic Agents• Background Transfer Service• Alarms and Reminders

DemoFast ApplicationSwitching

Application Lifecycle - Dormant

running

deactivated

dormant

activated

Phone resources detachedThreads & timers suspended

Fast App Resume

Save State!State preserved!e.IsApplicationInstancePreserved== true

Application Lifecycle - Tombstoned

running

deactivated

dormant Phone resources detachedThreads & timers suspended

Restore state!e.IsApplicationInstancePreserved == false

Resuming .. .

Tombstone the oldest app

tombstoned

activated

Methods & Events

7

Finding the Resume type

The Activation handler can test a flag to determine the type of resume taking place

private void Application_Activated(object sender, ActivatedEventArgs e){ if (e.IsApplicationInstancePreserved) { // Dormant - objects in memory intact } else { // Tombstoned - need to reload }}

Deactivation Resource ManagementDeactivated App

PhoneApplicationPage.OnNavigatedFrom

PhoneApplicationService.Deactivated

Framework:Detach Resources

Framework:Suspend Timers and Threads

Dormant App

MediaPlayer.PauseMediaElement.Pause

SoundEffectInstance.PauseVibrateController.StopPhotoCamera.Dispose

Save page/global state

XNA Audio Paused

Sensors Notifications suppressed

Networking Cancelled

Sockets Disconnected

MediaElement Disconnected

Camera Disposed

Activation Resource Management

MediaElement.Source/Position/PlaySocket.ConnectAsyncnew PhotoCamera/VideoCamera

Restore app state if tombstoned

Running App

PhoneApplicationPage.OnNavigatedTo

PhoneApplicationService.Activated

Framework:Attach Resources

Framework:Resume Timers and Threads

Dormant App

XNA Audio Resumed

Sensors Notifications resumed

Networking Completed with Cancellation

Sockets -

MediaElement -

Camera -

Isolated Storage vs State Storage• Isolated storage is so called because the data for an

application is isolated from all other applications • It can be used as filestore where an application can store folders

and files• It is slow to access, since it is based on NVRAM technology• It can also be used to store name/value pairs, e.g. program settings

• State storage is so called because it is used to hold the state of an application• It can be used to store name/value pairs which are held in memory

for dormant or tombstoned applications• It provides very quick access to data

11

DemoCaptain’s LogWith No StorageWith StorageFully Working

Fast App Switching and Tombstoning Review• Only one Windows Phone application is Active at any time• The Start and Back buttons on the phone are used to

start new applications and return to previously used ones• If an application is replaced by another it is either made

Dormant (still in memory but not running) or Tombstoned (removed from memory)

• Applications must use populate methods provided in the App.xaml.cs class to save and retrieve state information when appropriate• State can be stored in memory for quick reload and in isolated

storage which serve as a permanent store

Background Tasks

Multitasking Capabilities• Background Agents• Periodic• Resource Intensive

• Background Transfer Service• Alarms and Reminders• Background Audio

Background Agents• Agents• Periodic• Resource Intensive

• An app may have up to one of each • Initialized in foreground, run in background• Persisted across reboots

• User control through CPL• System maximum of 18 periodic agent

• Agent runs for up to 14 days (can be renewed)

Generic Agent TypesPeriodic Agents• Occurrence• Every 30 min

• Duration• ~15 seconds

• Constraints• <= 6 MB Memory• <=10% CPU

Resource Intensive Agents• Occurrence• External power• Non-cell network

• Duration• 10 minutes

• Constraints • <= 6 MB Memory

Background Agent Functionality

Allowed

Tiles Toast Location Network R/W ISO store Sockets Most framework APIs

Restricted

Display UI XNA libraries Microphone and Camera Sensors Play audio

(may only use background audio APIs)

DemoCaptain’s Location Log

Debugging a Background Task

• It would be annoying if we had to wait 30 minutes to get code in the agent running so we could debug it

• When we are debugging we can force service to launch itself

• Such code can be conditionally compiled and removed before the production version is built

#if DEBUG_AGENT ScheduledActionService.LaunchForTest(taskName,

TimeSpan.FromSeconds(60));#endif

Debugging the Agent Code• When you use the Back button or Start on the phone to interrupt

an application with an active Background Task ,Visual Studio does not stop running

• It remains attached to the application• You can then put breakpoints into the background task

application and debug them as you would any other program• You can single step, view the contents of variables and even

change them using the Immediate Window• This is also true if you are working on a device rather than the

emulator• The same techniques work on ResourceIntensiveAgents

DemoDebugging Tasks

File Transfer Tasks• It is also possible to create a background task to transfer

files to and from your application’s isolated storage• The transfers will continue to work even when the

application is not running• An application can monitor the state of the downloads and

display their status• Files can be fetched from HTTP or HTTPs hosts• At the moment FTP is not supported

• The system maintains a queue of active transfers and services each one in turn

• Applications can query the state of active transfers

Background Transfer Policies• There are a set of policies that control transfer

behaviour• Maximum Upload file size: 5Mb• Maximum Download file size over cellular (mobile phone)

data: 20Mb• Maximum Download file size over WiFi: 100Mb

• These can be modified by setting the value of TransferPreferences on a particular transfer

Transfer Management• An application can find out how many file transfers

it has active• It will have to do this when it is restarted, as file transfers

will continue even when the application is not running• It can then perform transfer management as

required• There is a good example of transfer list

management on MSDN:

• http://msdn.microsoft.com/en-us/library/hh202953.aspx

DemoPicture Fetch

Scheduled Notifications• Time-based, on-phone notifications• Supports Alerts & Reminders• Persist across reboots• Adheres to user settings• Consistent with phone UX

Alarms vs Reminders? Alarms Reminders

• Modal• Snooze and

Dismiss• Sound

customization• No app

invocation• No stacking

• Rich information• Integrates with

other reminders• Snooze and

Dismiss• Launch app• Follows the

phones global settings

Creating a Reminder

• This code creates a reminder and adds it as a scheduled service

• The value eggTime holds the length of the delay• This code also sets the url of the page in the application

using Microsoft.Phone.Scheduler;...eggReminder = new Reminder("Egg Timer");

eggReminder.BeginTime = DateTime.Now + new TimeSpan(0, eggTime, 0);eggReminder.Content = "Egg Ready";eggReminder.RecurrenceType = RecurrenceInterval.None;eggReminder.NavigationUri = new Uri("/EggReadyPage.xaml",

UriKind.Relative);

ScheduledActionService.Add(eggReminder);

Reminder Housekeeping

• Reminders are identified by name• This code finds the “Egg Timer” reminder and then

removes it from the scheduler

Reminder eggReminder = ScheduledActionService.Find("Egg Timer") as Reminder;

if ( eggReminder != null ) { ScheduledActionService.Remove("Egg Timer");}

DemoDemo4: Egg Timer

Audio Playback Agents• It is also possible to

create an Audio Playback Agent that will manage an application controlled playlist

• The mechanism is the same as for other background tasks

• The audio can be streamed or held in the application isolated storage

Background Audio• Playback• App provides URL or stream to Zune• Audio continues to play even if app is closed• App is notified of file or buffer near completion

• Phone Integration• Music & Video Hub• Universal Volume Control (UVC), lauch app, controls, contextual info• Contextual launch – Start menu, UVC, Music & Video Hub

• App Integration• App can retrieve playback status, progress, & metadata• Playback notification registration

Review• An application can create background processes• Periodic Task and ResourceIntensive task run when the application is

stopped• Scheduled notifications will fire whether the application is running

or not• Audio Playback run alongside the application

• Applications and their background processes can communicate via isolated storage

• Visual Studio can be used to debug background tasks in the same way as foreground applications

Be what’s next: Windows Phone• Find everything here

http://aka.ms/mbl-phone/start • Download your free Windows Phone Dev Tools

http://aka.ms/mbl-phone/tools• Channel9 ‘Get to Mango’ series

http://aka.ms/mbl-phone/mango• Register as a developer

http://aka.ms/mbl-phone/register

Follow me on Twitter

or the Puppy gets it@benriga

Q&A Ben RigaTechnical EvangelistWindows Phone

benriga@microsoft.com@benriga

© 2012 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.