Charles Petzold Application Lifecycle and State Management

Charles Petzoldwww.charlespetzold.com

Application Lifecycle andState Management

Agenda

• Launching and closing• Isolated storage• Activation and deactivation• Tombstoning• Page state and application state• Obscuration• Idle detection

• Phones run one app at a time– Apps not in foreground are closed or deactivated– Either way, process is terminated (usually)

• PhoneApplicationService fires lifecycle events– Launching and Closing– Activated and Deactivated

• State is not maintained when app is closed or deactivated unless you take steps to maintain it– Except in certain situations (more later)

Application Lifecycle

• Application is closed when:– Application's first page is displayed, and…– User presses the phone's Back button

• The only way to close an application!• Process is terminated; all state is lost

– One exception: if Back button is pressed quickly, WP7 may reconnect to still-running process

– But don't count on it

Launching and Closing

Launching and Closing Events

// App.xaml<shell:PhoneApplicationService Launching="Application_Launching" Closing="Application_Closing" ... />

// App.xaml.csvoid Application_Launching(object sender, LaunchingEventArgs e){}

void Application_Closing(object sender, ClosingEventArgs e){}

• Every Windows phone has a Back button• Page fires BackKeyPress events when the

Back button is pressed• From the UI Design and Interaction Guide

for Windows Phone 7:

Back Button

Developers should only implement Back Button behaviors that navigate back or dismiss context menus or modal dialog boxes. All other implementations are prohibited.

Prompting Before Exiting

BackKeyPress += new EventHandler<CancelEventArgs>(OnBackKeyPress); . . .private void OnBackKeyPress(object sender, CancelEventArgs e){ MessageBoxResult result = MessageBox.Show("Are you sure?", "Confirm", MessageBoxButton.OKCancel); e.Cancel = !(result == MessageBoxResult.OK);}

demoLaunching and Closing

• System.IO.IsolatedStorage namespace contains classes that provide access to virtual file system– IsolatedStorageFile– IsolatedStorageException– IsolatedStorageSettings

• Stored in memory on the phone• Permanently deleted if app is uninstalled• Not subject to quotas

Isolated Storage

• Provides methods for:– Opening and closing isolated storage stores

• Also known as "isostores"– Creating, opening, copying, enumerating,

moving, renaming, and deleting isolated storage files

– Creating, opening, enumerating, moving, renaming, and deleting isolated storage folders

• AvailableFreeSpace property provides information about free space

IsolatedStorageFile

• IsolatedStorageFile method for accessing per-application stores

GetUserStoreForApplication

App 1Store

App 2Store

Marketplace

App 1 App 2

Phone

Writing to Isolated Storage

using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication()){ using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream("Settings.xml", FileMode.Create, store)) { using (StreamWriter writer = new StreamWriter(stream)) { // TODO: Write to stream with StreamWriter } }}

Reading from Isolated Storage

using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication()){ if (store.FileExists("Settings.xml")) { using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream("Settings.xml", FileMode.Open, store)) { using (StreamReader reader = new StreamReader(stream)) { // TODO: Read from stream with StreamReader } } }}

Deleting an Isolated Storage Fileusing (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication()){ if (store.FileExists("Settings.xml")) store.DeleteFile("Settings.xml");}

• Dictionary stored in isolated storage– Application scope– Accessed through

IsolatedStorageSettings.ApplicationSettings property

• Simplifies task of storing user preferences and other simple settings– For example, language preferences

• Private to each application

Application Settings

Using ApplicationSettings

// Write to the ApplicationSettings dictionaryIsolatedStorageSettings settings = IsolatedStorageSettings.ApplicationSettings;settings["Culture"] = "fr-fr";

// Read from the ApplicationSettings dictionarystring culture;IsolatedStorageSettings settings = IsolatedStorageSettings.ApplicationSettings;if (settings.TryGetValue<string>("Culture", out culture)) HtmlPage.Window.Alert(culture);

Determining Available Space

using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication()){ Int64 available = store.AvailableFreeSpace; ...}

• Performance of CreateFile, OpenFile, and other methods degrades with large numbers of files

• Rule of thumb: Segregate files into folders, with no more than 128 files per folder– "How Many Files are Too Many Files?"

• http://appangles.com/blogs/mickn/wp7/?p=6• Block reads and writes are more performant

than lots of little reads and writes

Isolated Storage Performance

Creating an Isolated Storage Folderusing (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication()){ store.CreateDirectory("\XML Stuff");

using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream("\XML Stuff\Settings.xml", FileMode.Create, store)) { ... }}

demoIsolated Storage

• Application is deactivated when:– User presses the phone's Start button– App launches a launcher or chooser– Device time-out locks the screen

• Unless you specify otherwise• Deactivation usually means process is

terminated– Notable exception: When certain choosers such

as PhotoChooserTask are launched• Termination means all state is lost

Activation and Deactivation

Activated and Deactivated Events// App.xaml<shell:PhoneApplicationService Activated="Application_Activated" Deactivated="Application_Deactivated" ... />

// App.xaml.csvoid Application_Activated(object sender, ActivatedEventArgs e){}

void Application_Deactivated(object sender, DeactivatedEventArgs e){}

demoActivation and Deactivation

• Occurs when app is deactivated and terminated

• To restore app to same state when reactivated, persist state in application state or page state– Or use isolated storage if volume of data exceeds

limits on application state and page state– Isolated storage is 30% to 50% slower

• Use page's OnNavigatedFrom and OnNavigatedTo methods to save and restore state

• App is allowed 10 seconds to tombstone data

Tombstoning

• Data store for tombstoning global data– Limited to approx. 1.5 MB per app

• Dictionary accessed through PhoneApplicationService.State property

• Available between Activated and Deactivated events, inclusive

• Data must be serializable

Application State

Saving Application State

void Application_Deactivated(object sender, DeactivatedEventArgs e){ PhoneApplicationService.Current.State["x1"] = x1; PhoneApplicationService.Current.State["y1"] = y1; PhoneApplicationService.Current.State["x2"] = x2; PhoneApplicationService.Current.State["y2"] = y2;}

Restoring Application State

void Application_Activated(object sender, ActivatedEventArgs e){ if (PhoneApplicationService.Current.State.ContainsKey("x1")) x1 = (double)PhoneApplicationService.Current.State["x1"];

if (PhoneApplicationService.Current.State.ContainsKey("y1")) y1 = (double)PhoneApplicationService.Current.State["y1"];

if (PhoneApplicationService.Current.State.ContainsKey("x2")) x2 = (double)PhoneApplicationService.Current.State["x2"];

if (PhoneApplicationService.Current.State.ContainsKey("y2")) y2 = (double)PhoneApplicationService.Current.State["y2"];}

• Data store for tombstoning per-page data– Limited to 2 MB per page and 4 MB per app

• Dictionary accessed through PhoneApplicationPage.State property

• Available between OnNavigatedTo and OnNavigatedFrom methods, inclusive

• Data must be serializable

Page State

Saving Page State

protected override void OnNavigatedFrom(NavigationEventArgs e){ this.State["x1"] = x1; this.State["y1"] = y1; this.State["x2"] = x2; this.State["y2"] = y2;}

Restoring Page State

protected override void OnNavigatedTo(NavigationEventArgs e){ if (this.State.ContainsKey("x1")) x1 = (double)this.State["x1"];

if (this.State.ContainsKey("y1")) y1 = (double)this.State["y1"];

if (this.State.ContainsKey("x2")) x2 = (double)this.State["x2"];

if (this.State.ContainsKey("y2")) y2 = (double)this.State["y2"];}

demoTombstoning

Tombstoning a ListBox Control

protected override void OnNavigatedFrom(NavigationEventArgs e){ // Save the ListBox control's SelectedIndex in page state this.State["Index"] = ListBoxControl.SelectedIndex;} protected override void OnNavigatedTo(NavigationEventArgs e){ // Restore the ListBox control's SelectedIndex if (this.State.ContainsKey("Index")) ListBoxControl.SelectedIndex = (int)this.State["Index"];}

Tombstoning a Pivot Control

// This doesn't workprotected override void OnNavigatedFrom(NavigationEventArgs e){ // Save the Pivot control's SelectedIndex in page state this.State["Index"] = PivotControl.SelectedIndex;} protected override void OnNavigatedTo(NavigationEventArgs e){ // Restore the Pivot control's SelectedIndex if (this.State.ContainsKey("Index")) PivotControl.SelectedIndex = (int)this.State["Index"];}

Tombstoning a Pivot Control, Cont.// This worksprotected override void OnNavigatedFrom(NavigationEventArgs e){ // Save the Pivot control's SelectedIndex in page state this.State["Index"] = PivotControl.SelectedIndex;} // Handler for Pivot.Loaded eventvoid OnPivotControlLoaded(object sender, RoutedEventArgs e){ // Restore the Pivot control's SelectedIndex if (this.State.ContainsKey("Index")) _index = (int)this.State["Index"];}

Tombstoning a Panorama Control// This doesn't workprotected override void OnNavigatedFrom(NavigationEventArgs e){ // Save the Panorama control's SelectedIndex in page state this.State["Index"] = PanoramaControl.SelectedIndex;} protected override void OnNavigatedTo(NavigationEventArgs e){ // Restore the Panorama control's SelectedIndex if (this.State.ContainsKey("Index")) PanoramaControl.SelectedIndex = (int)this.State["Index"];}

Tombstoning a Panorama, Cont.// This worksprotected override void OnNavigatedFrom(NavigationEventArgs e){ // Save the Panorama control's SelectedIndex in page state this.State["Index"] = PanoramaControl.SelectedIndex;} protected override void OnNavigatedTo(NavigationEventArgs e){ // Restore the Panorama control's SelectedIndex if (this.State.ContainsKey("Index")) PanoramaControl.DefaultItem = PanoramaControl.Items[(int)State["Index"]];}

demoTombstoning Pivot Controls

• Fired by PhoneApplicationFrame– Obscured – Shell comes to the foreground– Unobscured – App returns to the foreground

• Common causes:– Phone receives an incoming call– Screen times out and lock screen appears

• If app has disabled idle detection• Some apps must handle these events to

pass certification requirements

Obscured and Unobscured Events

Handling Obscuration Events

(Application.Current as App).RootFrame.Obscured += OnObscured;(Application.Current as App).RootFrame.Unobscured += OnUnobscured; . . .private void OnObscured(object sender, ObscuredEventArgs e){ // Application is obscured by shell (possibly an incoming call) VibrateController.Default.Stop(); // Sample action}

private void OnUnobscured(object sender, EventArgs e){ // Application has returned to the foreground}

• By default, apps are deactivated when screen locks

• Apps can continue running when screen locks by disabling ApplicationIdleDetectionMode– Primarily for apps that are slow to reactivate– Also for apps that need to run under lock (e.g.,

audio)– Obscured and Obscured events replace

Activated and Deactivated events• Apps can also disable

UserIdleDetectionMode to prevent screen from locking automatically

Idle Detection

Disabling Application Idle Detection// Allow the app to run when screen is locked. Once disabled,// ApplicationIdleDetectionMode cannot be reenabled while the// app is running.

PhoneApplicationService.Current.ApplicationIdleDetectionMode = IdleDetectionMode.Disabled;

Disabling User Idle Detection

// Prevent screen from locking while this app runsPhoneApplicationService.Current.UserIdleDetectionMode = IdleDetectionMode.Disabled;

Detecting a Locked Screen

(Application.Current as App).RootFrame.Obscured += OnObscured;(Application.Current as App).RootFrame.Unobscured += OnUnobscured; . . .private void OnObscured(object sender, ObscuredEventArgs e){ if (e.IsLocked) { // Screen is locked }}

private void OnUnobscured(object sender, EventArgs e){ // Screen is no longer locked}

demoRunning Under a Locked Screen

Charles Petzoldwww.charlespetzold.com

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