Charles Petzold www.charlespetzold.com

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

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

3. Application Lifecycle • 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)

4. Launching and Closing • 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

5. Launching and Closing Events // App.xaml <shell:PhoneApplicationService Launching="Application_Launching" Closing="Application_Closing" ... /> // App.xaml.cs void Application_Launching(object sender, LaunchingEventArgse) { } void Application_Closing(object sender, ClosingEventArgse) { }

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

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

8. Launching and Closing

9. Isolated Storage • System.IO.IsolatedStoragenamespace 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

10. IsolatedStorageFile • 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

11. GetUserStoreForApplication • IsolatedStorageFile method for accessing per-application stores Marketplace App 1 App 2 App 1 Store Phone App 2 Store

12. 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 } } }

13. 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 } } } }

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

15. Application Settings • 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

16. Using ApplicationSettings // Write to the ApplicationSettings dictionary IsolatedStorageSettings settings = IsolatedStorageSettings.ApplicationSettings; settings["Culture"] = "fr-fr"; // Read from the ApplicationSettings dictionary string culture; IsolatedStorageSettings settings = IsolatedStorageSettings.ApplicationSettings; if (settings.TryGetValue<string>("Culture", out culture)) HtmlPage.Window.Alert(culture);

17. Determining Available Space using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication()) { Int64 available = store.AvailableFreeSpace; ... }

18. Isolated Storage Performance • 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

19. Creating an Isolated Storage Folder using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication()) { store.CreateDirectory("\XML Stuff"); using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream("\XML Stuff\Settings.xml", FileMode.Create, store)) { ... } }

20. Isolated Storage

21. Activation and Deactivation • 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

22. Activated and Deactivated Events // App.xaml <shell:PhoneApplicationService Activated="Application_Activated" Deactivated="Application_Deactivated" ... /> // App.xaml.cs void Application_Activated(object sender, ActivatedEventArgs e) { } void Application_Deactivated(object sender, DeactivatedEventArgse) { }

23. Activation and Deactivation

24. Tombstoning • 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

25. Application State • Data store for tombstoningglobal 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

26. Saving Application State void Application_Deactivated(object sender, DeactivatedEventArgse) { PhoneApplicationService.Current.State["x1"] = x1; PhoneApplicationService.Current.State["y1"] = y1; PhoneApplicationService.Current.State["x2"] = x2; PhoneApplicationService.Current.State["y2"] = y2; }

27. Restoring Application State void Application_Activated(object sender, ActivatedEventArgse) { 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"]; }

28. Page State • Data store for tombstoning per-page data • Limited to 2 MB per page and 4 MB per app • Dictionary accessed through PhoneApplicationPage.Stateproperty • Available between OnNavigatedTo and OnNavigatedFrom methods, inclusive • Data must be serializable

29. 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; }

30. 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"]; }

31. Tombstoning

32. Tombstoning a ListBox Control protected override void OnNavigatedFrom(NavigationEventArgse) { // Save the ListBoxcontrol's SelectedIndex in page state this.State["Index"] = ListBoxControl.SelectedIndex; } protected override void OnNavigatedTo(NavigationEventArgse) { // Restore the ListBoxcontrol's SelectedIndex if (this.State.ContainsKey("Index")) ListBoxControl.SelectedIndex= (int)this.State["Index"]; }

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

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

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

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

37. Tombstoning Pivot Controls

38. Obscured and Unobscured Events • 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

39. 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 }

40. Idle Detection • 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

41. Disabling Application Idle Detection // Allow the app to run when screen is locked. Once disabled, // ApplicationIdleDetectionMode cannot be reenabledwhile the // app is running. PhoneApplicationService.Current.ApplicationIdleDetectionMode = IdleDetectionMode.Disabled;

42. Disabling User Idle Detection // Prevent screen from locking while this app runs PhoneApplicationService.Current.UserIdleDetectionMode= IdleDetectionMode.Disabled;

43. 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 }

44. Running Under a Locked Screen

45. Questions? Charles Petzold www.charlespetzold.com