This document discusses fast application switching and tombstoning on Windows Phone. It describes how there is only one active app at a time and apps can be dormant (in memory but not running) or tombstoned (removed from memory). It provides examples of using application state management methods to save and restore state when an app becomes dormant or tombstoned. The document also demonstrates how to determine resume type and manage resources during activation and deactivation.

1. Fast Application
Switching &
Tombstoning

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

3. Demo
Demo 1:
Fast Application
Switching

4. Application Lifecycle - Dormant
Fast App Resume
running
State preserved!
e.IsApplicationInstancePreserved Save State!
== true
activated deactivated
dormant Phone resources
detached
Threads & timers
suspended
4 Windows Phone

5. Application Lifecycle - Tombstoned
Resuming .. .
Restore state!
e.IsApplicationInstancePreserved
== false
running
activated deactivated
Tombstone
the oldest
app
Tombstoned dormant Phone resources detached
Threads & timers suspended
5 Windows Phone

6. Methods & Events
6 Windows Phone 6

7. Finding the Resume type
private void Application_Activated(object sender, ActivatedEventArgs e)
{
if (e.IsApplicationInstancePreserved)
{
// Dormant - objects in memory intact
}
else
{
// Tombstoned - need to reload
}
}
 The Activation handler can test a flag to determine the type of resume
taking place
7 Windows Phone

8. Deactivation Resource Management
MediaPlayer.Pause
MediaElement.Pause
SoundEffectInstance.Pause
VibrateController.Stop
PhotoCamera.Dispose
Save page/global state
XNA Audio Paused
Sensors Notifications suppressed
Networking Cancelled
Sockets Disconnected
MediaElement Disconnected
Camera Disposed
8 Windows Phone

9. Activation Resource Management
MediaElement.Source/Position/
Play
Socket.ConnectAsync
new PhotoCamera/VideoCamera
Restore app state if tombstoned
XNA Audio Resumed
Sensors Notifications resumed
Networking Completed with Cancellation
Sockets -
MediaElement -
Camera -
9 Windows Phone

10. 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
1
Windows Phone 10
0

11. Captain’s Log
Demo
• With No Storage
• With Storage
• Fully Working

12. 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
1
Windows Phone 12
2

13. Background Tasks

14. Multitasking Capabilities
 Background Agents
 Periodic
 Resource Intensive
 Background Transfer Service
 Alarms and Reminders
 Background Audio
1
Windows Phone 14
4

15. 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)
1
Windows Phone
5

16. Generic Agent Types
Periodic Agents Resource Intensive
 Occurrence Agents
 Every 30 min  Occurrence
 Duration  External power
 ~15 seconds  Non-cell network
 Constraints  Duration
 <= 6 MB Memory  10 minutes
 <=10% CPU  Constraints
 <= 6 MB Memory
1
Windows Phone
6

17. Background Agent Functionality
Allowed Restricted
 Tiles
 Toast  Display UI
 Location  XNA libraries
 Network  Microphone and Camera
 R/W ISO store  Sensors
 Sockets  Play audio
(may only use background audio APIs)
 Most framework APIs
1
Windows Phone
7

18. Demo
Demo1: Captain’s Location Log

19. Debugging a Background Task
#if DEBUG_AGENT
ScheduledActionService.LaunchForTest(taskName,
TimeSpan.FromSeconds(60));
#endif
 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
1
Windows Phone 19
9

20. 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
2
Windows Phone 20
0

21. Demo
Demo2: Debugging Tasks

22. 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
2
Windows Phone 22
2

23. 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
2
Windows Phone 23
3

24. 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
2
Windows Phone
4

25. Demo
Demo3: Picture Fetch

26. Scheduled Notifications
 Time-based, on-phone notifications
 Supports Alerts & Reminders
 Persist across reboots
 Adheres to user settings
 Consistent with phone UX
2
Windows Phone 26
6

27. Alarms vs Reminders?
Alarms Remind
ers
• Modal • Rich information
• Snooze and Dismiss • Integrates with other
• Sound customization reminders
• No app invocation • Snooze and Dismiss
• No stacking • Launch app
• Follows the phones global
27 settings

28. Creating a Reminder
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);
 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
2
Windows Phone 28
8

29. Reminder Housekeeping
Reminder eggReminder = ScheduledActionService.Find("Egg Timer")
as Reminder;
if ( eggReminder != null )
{
ScheduledActionService.Remove("Egg Timer");
}
 Reminders are identified by name
 This code finds the “Egg Timer” reminder and then removes it from the
scheduler
2
Windows Phone 29
9

30. Demo
Demo4: Egg Timer

31. 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
3
Windows Phone 31
1

32. 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
3
Windows Phone 32
2

33. 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
3
Windows Phone 33
3