Fast Application Switching & Tombstoning

Windows Phone

Topics

The Windows Phone execution model

Application State Management

Fast Application Switching

Dormant programs and Tombstoning

Application Navigation and Application Switching

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Demo

Demo 1: Fast Application Switching

Windows Phone

Application Lifecycle - Dormant

running

deactivated

dormant

activated

Phone resources

detached

Threads & timers

suspended

Fast App Resume

Save State! State preserved! e.IsApplicationInstancePreserved

== true

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Windows Phone

Application Lifecycle - Tombstoned

running

deactivated

dormant Phone resources detached

Threads & timers suspended

Restore state! e.IsApplicationInstancePreserved

== false

Resuming .. .

Tombstone

the oldest

app

Tombstoned

activated

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Windows Phone

Methods & Events

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Windows Phone

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 } }

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Windows Phone

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

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Windows Phone

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 -

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Windows Phone

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

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Demo

• With No Storage • With Storage • Fully Working

Captain’s Log

Windows Phone

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

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Background Tasks

Windows Phone

Multitasking Capabilities

Background Agents

Periodic

Resource Intensive

Background Transfer Service

Alarms and Reminders

Background Audio

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Windows Phone

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)

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Generic Agent Types

Periodic 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

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Windows Phone

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)

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Demo

Demo1: Captain’s Location Log

Windows Phone

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

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#if DEBUG_AGENT ScheduledActionService.LaunchForTest(taskName, TimeSpan.FromSeconds(60)); #endif

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Windows Phone

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

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Demo

Demo2: Debugging Tasks

Windows Phone

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

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Windows Phone

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

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Windows Phone

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

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Demo

Demo3: Picture Fetch

Windows Phone

Scheduled Notifications

Time-based, on-phone notifications

Supports Alerts & Reminders

Persist across reboots

Adheres to user settings

Consistent with phone UX

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Alarms vs Reminders?

Alarms

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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

Windows Phone

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

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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);

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Windows Phone

Reminder Housekeeping

Reminders are identified by name

This code finds the “Egg Timer” reminder and then removes it from the scheduler

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

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Demo

Demo4: Egg Timer

Windows Phone

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

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Windows Phone

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

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Windows Phone

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

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