Data management
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SharedPreferences stores private primitive data, is automatically persisted between sessions, and is often used for customizable app settings. SQLite databases store larger amounts of structured private data locally. Internal storage saves smaller private data sets while external storage saves larger non-private data. The document provides examples of using these storage options to save and retrieve data like preferences, images and database records in an Android app.
Data management
- 3. Small amounts of primitive data
- 4. Small to medium amounts of private data
- 5. Larger amounts of non-private data
- 6. Store small to large amounts of private, structured data
- 7. A persistent map Holds key-value pairs of simple data types Automatically persisted across application sessions
- 8. Often used for long-term storage of customizable application data Account name Favorite WiFi networks User customizations
- 9. To get a SharedPreference object associated with a given Activity Activity.getPreferences (int mode) MODE_PRIVATE
- 10. Context.getSharedPreferences (" String name, int mode) name – name of SharedPreferences file Mode – MODE_PRIVATE
- 12. Add values to SharedPreferences using SharedPreferences.Editor instance putInt(String key, int value) putString(String key, String value) remove(String key)
- 13. Commit edited values with SharedPreferences.Editor.commit()
- 14. Use SharedPreferences methods to read values getAll() getBoolean(String key, …) getString(String key, …)
- 15. When the user presses the play button, the application displays a random number The application keeps track of the highest number seen so far
- 19. A Class that supports displaying & modifying user preferences
- 20. This application displays a PreferenceFragment, which allows the user to enter and change a persistent user name
- 24. Class represents a file system entity identified by a pathname
- 25. Storage areas are classified as internal or external Internal memory usually used for smaller, application private data sets External memory usually used for larger, non-private data sets
- 26. FileOutputStream openFileOutput (String name, int mode) Open private file for writing. Creates the file if it doesn't already exist FileInputStream openFileInput (String name) Open private file for reading Many others. See documentation.
- 27. If a text file does not already exist, application writes text to that text file Application then reads data from the text file and displays it
- 31. Removable media may appear/disappear without warning
- 32. String Environment. getExternalStorageState() MEDIA_MOUNTED - present & mounted with read/write access MEDIA_MOUNTED_READ_ONLY - present & mounted with read-only access MEDIA_REMOVED - not present Etc.
- 33. Permission to write external files <uses-permission android:name= " “android.permission." WRITE_EXTERNAL_STORAGE" />
- 34. Application reads an image file from the resources directory Copies that file to external storage Reads image data from the file in external storage then displays the image
- 38. Temporary files that may be deleted by the system when storage is low Files removed when application uninstalled
- 39. File Context.getCacheDir() Returns absolute path to an application-specific directory that can be used for temporary files
- 40. Context.getExternalCacheDir() returns a File representing external storage directory for cache files
- 41. SQLite provides in-memory database Designed to operate within a very small footprint (<300kB) Implements most of SQL92 Supports ACID transactions Atomic, Consistent, Isolated & Durable
- 42. Recommended method relies on a helper class called SQLiteOpenHelper
- 43. Subclass SQLiteOpenHelper Call super() from subclass constructor to initialize underlying database
- 44. Override onCreate() Override onUpgrade() Execute CREATE TABLE commands
- 45. Use SQLiteOpenHelper methods to open & return underlying database Execute operations on underlying database
- 46. Application creates an SQLite database and inserts records, some with errors, into it When user presses the Fix button, the application deletes, updates and redisplays the corrected database records
- 52. Databases stored in /data/data/<package name>/databases/ Can examine database with sqlite3 # adb -s emulator-5554 shell # sqlite3 /data/data/ course.examples.DataManagement.Data BaseExample/databases/artist_dbd
- 53. ContentProvider