Ch6 file, saving states, and preferences
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This document discusses various techniques for persisting application data in Android, including: 1. SharedPreferences which allow storing key-value pairs that can be shared within an app but not between apps. 2. Saving activity instance state by overriding onSaveInstanceState() which is called when an activity may be destroyed. 3. Preference frameworks for creating settings screens using XML preference hierarchies and listeners for updates. 4. Reading and writing files using openFileInput() and openFileOutput() which are restricted to the app's directory. 5. Including static resource files in the res/raw folder to bundle with the app.
Ch6 file, saving states, and preferences
- 1. Ch6. File, Saving States, and Preferences Browny 30, May, 2011
- 2. Outline • Saving Simple Application Data • Creating and Saving Preferences • Retrieving Shared Preferences • Preference Activity and Framework • Saving Activity State • Saving and Loading Files • Including Static File as Resources • File Management Tools
- 3. Saving Simple Application Data • 3 data-persistence techniques ‣ Shared Preferences (key/value pairs, can be shared among applica8on components in the same applica8on context, but not available to other applica8ons) ‣ Saved Applica2on data (A pair of event handlers used for saving Ac8vity instance details) ‣ Files
- 4. Creating and Saving Preferences • Create or Modify a Shared Preference: call getSharedPreferences • To modify a Shared Preference use the SharedPreferences.Editor class
- 6. Preference Activity and Framework (1/2) • Android offers an XML-driven framework to create system-style preference screens for your applications • 2 advantages ‣ Familiarity ‣ Integrate se@ngs screens from other applica8ons into your applica8on’s se@ngs screens
- 7. Preference Activity and Framework (2/2) • 3 parts of Preference Activity Framework ‣ Preference Screen Layout (An XML file that defines the hierarchy displayed in your Preference Ac8vity) ‣ Preference Ac2vity (An extension of PreferenceAc(vity that will be used to host your applica8on preference screens) ‣ Shared Preference Change Listener (An implementa8on of the onSharedPreferenceChangeListener class)
- 8. Preference Screen Layout (1/2) • Stored in the res/xml resources folder • Nested Preference Screen elements (each will be represented as a selectable element that will display a new screen if clicked)
- 9. Preference Screen Layout (2/2) • The specific attributes available for each preference, at least the following 4 ‣ android:key, android:+tle, android:summary, android:defaultValue
- 10. Native Preference Controls • CheckBoxPreference • EditTextPreference • ListPreference (equivalent of a spinner) • RingtonePreference (useful when you’re constructing a screen to configure notification settings) • Extending the Preference class
- 11. Using Intents to Import System Preference Screens (1/2) • Preference hierarchies can include Preference Screens from other applications (including system Preference Screens) • Useful for including links to relevant system Preference Screens within your own application settings
- 12. Using Intents to Import System Preference Screens (2/2) • Make your own Preference Screens available for invocation using intent, simply add an Intent Filter to the manifest entry for the host Preference Activity
- 13. Preference Activity • Host the preference hierarchy defined using the preferences XML file (extend the PreferenceActivity) • To display the application settings hosted in this Activity (call startActivity or startActivityForResult)
- 14. Finding/Using Shared Preferences • The Shared Preference values recorded for the options presented in a Preference Activity are stored against the application Context
- 15. Shared Preference Change Listeners (1/2) • A callback (onSharedPreferenceChangeListener) whenever a particular Shared Preference value is added, removed, or modified • Using this handler your application components can listen for changes to user preferences and update their UIs or behavior as required
- 16. Shared Preference Change Listeners (2/2)
- 17. Saving Activity State (1/2) • When: ‣ Want to save Ac8vity informa8on that doesn’t need to be shared with other components • How ‣ Call Ac(vity.getPreferences() without specifying a Shared Preferences name • What ‣ Access to the returned Shared Preferences map is restricted to the calling Ac8vity; each Ac8vity supports a single unnamed Shared Preferences object
- 18. Saving Activity State (2/2)
- 19. Saving and Restoring Instance State (1/2) • Saving (onSaveInstanceState event handler) ‣ Be triggered whenever an Ac8vity completes its ac8ve lifecycle. Only when it’s not being explicitly finished (with a call to finish)
- 20. Saving and Restoring Instance State (2/2) • Restoring ‣ The saved Bundle is passed in to the onRestoreInstanceState and onCreate methods if the applica8on is forced to restart during a session
- 21. Saving and Loading Files • Android offers openFileInput and openFileOuput to simplify reading and writing streams from and to local files • Support only those files in the current application folder; specifying path separators will cause an exception to be thrown • Files created using the openFileOuput method are private to the calling application
- 22. Including Static Files as Resources • Application requires external file resources, include them in your distribution package by placing them in the res/raw folder of your project hierarchy • Android’s resource mechanism lets you specify alternative resource files for different languages, locations, and hardware configurations
- 23. File Management Tools • Android supply some specialized utilities for file management that are available from the application Context ‣ deleteFile (Enables you to remove files created by the current applica8on) ‣ fileList (Returns a string array that includes all the files created by the current applica8on) • Useful for cleaning up temporary files left behind if your application crashes or is killed unexpectedly
- 24. Thank you :)