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Charles Petzold www.charlespetzold.com Application Lifecycle and State Management

Charles Petzold Application Lifecycle and State Management

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Page 1: Charles Petzold  Application Lifecycle and State Management

Charles Petzoldwww.charlespetzold.com

Application Lifecycle andState Management

Page 2: Charles Petzold  Application Lifecycle and State Management

Agenda

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

Page 3: Charles Petzold  Application Lifecycle and State Management

• 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

Page 4: Charles Petzold  Application Lifecycle and State Management

• 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

Page 5: Charles Petzold  Application Lifecycle and State Management

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){}

Page 6: Charles Petzold  Application Lifecycle and State Management

• 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.

Page 7: Charles Petzold  Application Lifecycle and State Management

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);}

Page 8: Charles Petzold  Application Lifecycle and State Management

demoLaunching and Closing

Page 9: Charles Petzold  Application Lifecycle and State Management

• 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

Page 10: Charles Petzold  Application Lifecycle and State Management

• 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

Page 11: Charles Petzold  Application Lifecycle and State Management

• IsolatedStorageFile method for accessing per-application stores

GetUserStoreForApplication

App 1Store

App 2Store

Marketplace

App 1 App 2

Phone

Page 12: Charles Petzold  Application Lifecycle and State Management

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 } }}

Page 13: Charles Petzold  Application Lifecycle and State Management

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 } } }}

Page 14: Charles Petzold  Application Lifecycle and State Management

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

Page 15: Charles Petzold  Application Lifecycle and State Management

• 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

Page 16: Charles Petzold  Application Lifecycle and State Management

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);

Page 17: Charles Petzold  Application Lifecycle and State Management

Determining Available Space

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

Page 18: Charles Petzold  Application Lifecycle and State Management

• 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

Page 19: Charles Petzold  Application Lifecycle and State Management

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)) { ... }}

Page 20: Charles Petzold  Application Lifecycle and State Management

demoIsolated Storage

Page 21: Charles Petzold  Application Lifecycle and State Management

• 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

Page 22: Charles Petzold  Application Lifecycle and State Management

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){}

Page 23: Charles Petzold  Application Lifecycle and State Management

demoActivation and Deactivation

Page 24: Charles Petzold  Application Lifecycle and State Management

• 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

Page 25: Charles Petzold  Application Lifecycle and State Management

• 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

Page 26: Charles Petzold  Application Lifecycle and State Management

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;}

Page 27: Charles Petzold  Application Lifecycle and State Management

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"];}

Page 28: Charles Petzold  Application Lifecycle and State Management

• 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

Page 29: Charles Petzold  Application Lifecycle and State Management

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;}

Page 30: Charles Petzold  Application Lifecycle and State Management

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"];}

Page 31: Charles Petzold  Application Lifecycle and State Management

demoTombstoning

Page 32: Charles Petzold  Application Lifecycle and State Management

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"];}

Page 33: Charles Petzold  Application Lifecycle and State Management

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"];}

Page 34: Charles Petzold  Application Lifecycle and State Management

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"];}

Page 35: Charles Petzold  Application Lifecycle and State Management

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"];}

Page 36: Charles Petzold  Application Lifecycle and State Management

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"]];}

Page 37: Charles Petzold  Application Lifecycle and State Management

demoTombstoning Pivot Controls

Page 38: Charles Petzold  Application Lifecycle and State Management

• 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

Page 39: Charles Petzold  Application Lifecycle and State Management

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}

Page 40: Charles Petzold  Application Lifecycle and State Management

• 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

Page 41: Charles Petzold  Application Lifecycle and State Management

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;

Page 42: Charles Petzold  Application Lifecycle and State Management

Disabling User Idle Detection

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

Page 43: Charles Petzold  Application Lifecycle and State Management

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}

Page 44: Charles Petzold  Application Lifecycle and State Management

demoRunning Under a Locked Screen

Page 45: Charles Petzold  Application Lifecycle and State Management

Charles Petzoldwww.charlespetzold.com

Questions?