07 wp7 application lifecycle

Application
Lifecycle
Jason Lee
Ethos Technologies

Agenda
Interruptions & User Expectations
Application Lifecycle
Tombstoning
Lifecycle Events
Resource Management
Play Time
Q & A

Interruptions
Interruption comes from
A user action (i.e. press the start button)
An external event (an incoming phone call)
An internal action (i.e. taking a photo, choosing a contact)
Interruption characteristics
Interruptions are not predictable
Interruptions tend to happen frequently

User Expectations
Phone and Applications
Phone is resource-constrained device, therefore we need to consume resources carefully
Phone is different from Desktop OS, which can hold multiple windows running processes simultaneously
However…
A user expects the application to be able to remain in the state where it was left
Microsoft development guideline requires application to provide such illusions that it keeps running continuously until it is get killed

Application Lifecycle
Running
Dormant
Tombstoned
Deactivated
Deactivated
Dead, and no longer
lives in memory.
But with something
carved on a Tombstone
Phone resources detached
Threads & Timers suspended
But app instance remains in memory
Activated
e.Preserved == true
Fast App Resume
Activated
e.Preserved == false
You Will See Resuming Process Bar

Tombstoning
When an app is tombstoned, it means
The app is dead
Some relevant data is saved by System for the app/page, which is called State information
When user navigates back
System restarts the application, passes applications state back to the App
System navigates to the very page where it was left, passes page state back to the Page
Developers should
Write code to save state before the app gets tombstoned
Write code to restore state after the app is reactivated from tombstoned

Lifecycle Events - App
Application_Launching
Fired when the application is started
Not fired when the application is reactivated
Load app settings/configuration
Application_Activated
Fired when the application is reactivated (brought to foreground)
Not fired when the application is started
Restore app state if tombstoned
Application_Deactivated
Fired when the application is deactivated (sent to background)
Not fired when the application is closed
Save app state as needed
Application_Closing
Fired when the application is closing (i.e. user presses Back key)
Not fired when the application is deactivated
Save app settings/configuration

Lifecycle Events - Page
OnNavigatedTo
Fired when the application is started
Not fired when the application is reactivated
Restore page state if tombstoned
OnNavigatedFrom
Fired when the application is deactivated (sent to background)
Not fired when the application is deactivated
Save page state as needed

Code Sample - 1
Application_Launching
Load app settings/configuration

Code Sample - 2
Application_Closing
You have only 10 seconds to finish all job
If you’ve got complex data to save, it’s recommended to save your data while the app is running at appropriate points

Code Sample - 3
Application_Deactivated
Save app state as needed

Code Sample - 4
Application_Activated

Time Limits

Resource Management - 1
Deactivating App
Page.
OnNavigatedFrom
- You may release phone resources, but not necessarily, the framework is doing it anyway
- You MUST Save app/page state
App.
Deactivated
Framework:
Detach Resources
Framework:
Suspend Timers and Threads
Dormant App

Resource Management - 2
Running App
Page.
OnNavigatedTo
MediaElement : Reset Source/Position
Socket : Reconnect
Camera: Recreate Object
App.
Activated
Framework:
Attach Resources
Framework:
Resume Timers and Threads
Dormant App

Take It Serious
It is required, not just recommended !
Microsoft tries its best to keep apps in the line, providing consistent user experience to end users.
It is about money !
If your app does not handle lifecycle issues, then it will be disqualified to be published on marketplace.

Play Time !
Goals
To understand various lifecycle events and orders of occurring under different situations
To be able to store and retrieve state information
To understand how tombstoning works

Tip
To test tombstoning on emulator

! & ?
Thank You !
Any Questions ?

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07 wp7 application lifecycle

by Tao on Jul 20, 2011

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07 wp7 application lifecycle — Presentation Transcript