The story of state - PowerPoint Presentation

Slide1

The story of stateApp data, settings, and the process lifecycle

Kraig Brockschmidt

Senior Program Manager, Windows Ecosystem Team

Author,

Programming Windows 8 Apps with HTML, CSS, and

JavaScript

3-126Slide2

Look at stateful apps from the perspective of state itselfWhat is its purpose

Where does it live

What affects and modifies state

AgendaSlide3

The purpose of state is to maintain a consistent

app experience across

sessions, devices, and process

lifecycle events Slide4

The user experience: apps are

stateful

Apps don’t start in an uninitialized state, even on first run

Persistent settings are always in effect

Settings that are user-specific but not device-specific can roam across devices (like account setups)

The settings charm is where users manage relevant state

Transient session state (like

unsubmitted

form data and navigation history) is preserved across sessions if and only if Windows terminates an app

User data is more app-independentSlide5

State is persistent

State exists when apps aren’t running or in memory at all

State carries user preferences across sessions

State carries transient session data across suspend, terminate, and restart

State can roam across a user’s devices

State can be modified by background tasks

State is versioned independently of apps (and less often)Slide6

Review of process lifecycle events

Running

app

Suspended

app

Suspending

Terminated

appLow resources

Code gets to run

App frozen

App not running

Resuming

App gets

5 seconds

to handle suspend

App is

not

notified before termination

Apps are notified when they have been resumed

User

launches app

Splash screen

Limited background tasks can runSlide7

Demo

Stateful

appsSlide8

The big picture of state

In memory

(app

changes variables

)

Running

Suspended

Not runningSystem restartOther devicesLocal/temp app data (modified by WinRT and other APIs)Includes databases (SQLite, IndexedDB, ESE/Jet) and other facilities built on appdata (HTML AppCache, local storage, third-party libraries)

Roaming

app

d

ata

(modified by WinRT and other APIs), sync’d to

cloud (within quota)

Windows.Storage.AccessCache (modified by WinRT API)

Windows.Storage.PasswordVault (modified by WinRT API), sync’d to cloudSlide9

Basic state settings (C#)

using

Windows.Storage;

// Create a simple setting

ApplicationDataContainer

localSettings =

ApplicationData.Current.LocalSettings;localSettings.Values["message"] = "Hello World";

Object value = localSettings.Values["message"];// Create a setting in a containerApplicationDataContainer container = localSettings.CreateContainer( "exampleContainer", ApplicationDataCreateDisposition.Always);localSettings.Containers["exampleContainer"].Values["message"] = "Hello World"

;Object value = localSettings.Containers["exampleContainer"].Values[

"message"

];Slide10

Basic files (C#)

using

Windows.Storage

;

//

Write a file

StorageFolder roamingFolder = ApplicationData.Current.roamingFolder;StorageFile file = await

roamingFolder.CreateFileAsync(filename, CreationCollisionOption.ReplaceExisting);await FileIO.WriteTextAsync(file, counter.ToString());// Read a fileStorageFile file = await

roamingFolder.GetFileAsync(filename);string text = await

FileIO

.ReadTextAsync(file);Slide11

Composite + HighPriority roaming (C#)

using

Windows.Storage

;

ApplicationDataContainer

roamingSettings =

ApplicationData.Current.RoamingSettings;ApplicationDataCompositeValue composite = new

ApplicationDataCompositeValue();composite["readerSet"] = "Liam's Books";composite["page"] = 524;roamingSettings.Values["HighPriority"] = composite;Slide12

DataChanged event (C#)

using

Windows.Storage;

// DataChanged is fired when new data has been roamed to this device

applicationData.DataChanged +=

new

TypedEventHandler<ApplicationData, object> (DataChangedHandler);async void

DataChangedHandler(Windows.Storage.ApplicationData appData, object o){ // DataChangeHandler may be invoked on a background thread, so use the // Dispatcher to invoke the UI-related code on the UI thread. Not needed // in JavaScript. await this.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => { // Handle new data });}Slide13

Access cache (C#)

using

Windows.Storage;

using

Windows.Storage.AccessCache;

// First permission granted by folder picker

StorageFolder folder = await folderPicker.PickSingleFolderAsync();if (folder != null){ // Remember permission for future access to the folder

// (including other sub-folder contents) StorageApplicationPermissions.FutureAccessList.AddOrReplace( "PickedFolderToken", folder);}// Retrieve cached permission (in a later session)StorageFolder folder2 = await StorageApplicationPermissions.FutureAccessList

.getFolderAsync("PickedFolderToken");Slide14

Credential Locker

For securely storing passwords apps should neither store nor roam passwords independently

On trusted PCs, these are roamed with the user

Also note CredentialPicker API

Sample:

http://bit.ly/OUr8LC

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Credential Picker & Locker (C#)

using

Windows.Security.Credentials;

using

Windows.Security.Credentials.UI;

CredentialPickerOptions

credPickerOptions = new CredentialPickerOptions();// Set options like captions, messages, protocol, etc.var res = await CredentialPicker

.PickAsync(credPickerOptions);PasswordVault vault = new PasswordVault();// Password typically encrypted already from UI...but this is good for plain textPasswordCredential c = new PasswordCredential("myCreds", res.CredentialUserName, res.CredentialPassword);vault.Add(c);

// To retrieve later onPasswordCredential cred = vault.Retrieve(

"myCreds"

, userName);Slide16

Additional AppData APIs

All languages

SQLite:

http://bit.ly/MuzL1e

(Tim

Heuer’s

blog)ESE/Jet APIs (Win32): http://bit.ly/ToslcK (reference); for JavaScript needs a WinRT componentJavaScript onlyIndexedDB: http://bit.ly/RyT9uk (reference) http://bit.ly/P5H292 (sample)HTML5 localStorage: http://www.w3.org/TR/webstorage/ HTML5 AppCache: http://dev.w3.org/html5/spec/offline.htmlSlide17

State versioning

Applies to the entire contents of

AppData

Managed through SetVersionAsync

No relationship to app version: many app versions can and will likely use the same version of state

On launch, app should migrate old state if found, and call

SetVersionAsync to update the versionCloud service for roaming data maintains multiple versions until all apps have upgradedCan use ServicingComplete background task trigger to migrate state when an app update is installedSlide18

Settings UI

Settings is a ubiquitous app feature, hence the charm

Settings charm eliminates need to have specific settings pages within the app’s navigation hierarchy

Use for state and configuration that the user can control

Accounts, preferences, etc.

Specifying what roams and what doesn’t

State that app maintains silently doesn’t need to appear hereApp’s settings flyouts are just pieces of UI with unique means of invoking them; typically write to persistent stateSlide19

Settings API

App responds to

Windows.UI.ApplicationSettings.CommandsRequested

eventApp populates commandsLinks: help, privacy statement, terms of use, etc.Panels: invoke

flyouts

that change app data

System provides permissions, rate and reviewSettings flyout controlsXAML: Windows.UI.Xaml.Controls.SettingsFlyoutJavaScript: WinJS.UI.SettingsFlyoutSlide20

Demo

SettingsSlide21

Background tasks for state

Maintenance triggers

Run periodically on AC power

Useful for cleaning up temp stateSystem triggers

AC power, non-lock screen

InternetAvailable

, NetworkStateChange for connectivityServicingComplete: perfect time to migrate app state versionsLock screen triggers (AC or battery power)Session Connected, UserPresent, UserAway, TimeTriggerAll tasks subject to CPU and network activity quotasIndependent of main app (can use mixed languages)Slide22

Demo

Background tasks for stateSlide23

Best practices for apps

Launch with initial defaults

JavaScript: use

sessionState object as a namespace for variablesC#/VB/C++: Use

SuspensionManager

helpers

Write session and persistent state incrementally as it changesDon’t leave this for the suspending event unless necessaryAlways save file references in access cache—never save pathsSome files/folders don’t come from the file system!Always save passwords in the Credential LockerUse encryption for security, compression to minimize sizeSlide24

Best practices for apps

Session state: restore if launched after terminated

Typically only a few pieces of data

Session state is not restored if app is launched to service contracts or launch argumentsException: search

Launch arguments means file type activation or secondary tile

Check elapsed time and refresh when resuming

Especially data from online servicesSlide25

10/31 145p – Kodiak – Introduction to creating Windows Store apps using XAML (3-116)

10/30 215p – Kodiak – Introduction to creating a Windows Store App using HTML and JavaScript (3-115)

11/1 830a – Kodiak – Alive with activity: Tiles, notifications, and

background tasks (3-101)

Related sessionsSlide26

Application data sample

Launching, resuming, and multitasking

Background task sample

Programming Windows 8 Apps in HTML, CSS, and JavaScript

ResourcesSlide27

Develop:

http

://msdn.microsoft.com/en-US/windows/apps/br229512

Design:

http://design.windows.com/

Samples: http://code.msdn.microsoft.com/windowsapps/Windows-8-Modern-Style-App-SamplesVideos: http://channel9.msdn.com/WindowsResourcesPlease submit session evals by using the Build Windows 8 appor at http://aka.ms/BuildSessionsSlide28