DataManagement

DataManagement - Single Application Persistent Data...

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Unformatted text preview: Single Application Persistent Data Storage   Files   SharedPreferences   SQLite database   Represents a file system entity identified by a pathname   Storage areas classified as internal or external   Internal memory usually used for application private files   External memory used for public files   boolean isDirectory()   Return true if this File represents a directory   String getAbsolutePath()   Returns the absolute path to this File   boolean setReadable(boolean readable)   Sets read permission on this File   Many others. See documentation. // Open file with ContextWrapper.openFileOutput() FileOutputStream fos = openFileOutput(fileName, MODE_PRIVATE); PrintWriter pw = new PrintWriter( new BufferedWriter(new OutputStreamWriter(fos))); // Write to file pw.println(…); … // Close file pw.close(); // Open file with ContextWrapper.openFileInput() FileInputStream fis = openFileInput(fileName); BufferedReader fr = new BufferedReader(new InputStreamReader(fis)); String line = ""; // Read from file while (null != (line = fr.readLine())) { // process data } // Close file fr.close();   Cache files are temporary files that may be deleted by the system when storage is low   File Context.getCacheDir()   Returns absolute path to an application ­specific directory that can be used for temporary files   Files removed when application uninstalled     Removable media may appear/disappear without warning 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   Need permission to write external files   <uses ­permission android:name= “android.permission.WRITE_EXTERNAL_STORAGE" /> public class FileWriteAndReadActivity extends Activity { public void onCreate(Bundle savedInstanceState) { … if (Environment.MEDIA_MOUNTED.equals( Environment.getExternalStorageState())) { File outFile = new File(getExternalFilesDir( Environment.DIRECTORY_PICTURES),fileName); try { BufferedOutputStream os = new BufferedOutputStream(new FileOutputStream(outFile)); BufferedInputStream is = new BufferedInputStream(getResources() .openRawResource(R.drawable.icon)); copy(is, os); } catch (FileNotFoundException e) {} } } … private void copy(InputStream is, OutputStream os) { final byte buf = new byte[1024]; int numBytes; try { while ( ­1 != (numBytes = is.read(buf))) { os.write(buf, 0, numBytes); } } catch (IOException e) {… } finally { try { is.close(); os.close(); } catch (IOException e) {} …   Context.getExternalCacheDir() returns a File representing external storage directory for cache files   Files removed when application uninstalled   A persistent map   Holds key ­value pairs of simple data types   Automatically managed across application uses   Often used for long ­term storage of customizable application data such as user preferences, e.g.,   User ID   Favorite WiFi networks   Activity.getPreferences (int mode)   Mode: MODE_PRIVATE, MODE_WORLD_READABLE or MODE_WORLD_WRITEABLE   Returns a SharedPreference object for the current Activity   Context.getSharedPreferences ( String name, int mode)   name – name of SharedPreference file   Mode – MODE_PRIVATE, MODE_WORLD_READABLE or MODE_WORLD_WRITEABLE   Returns named SharedPreference object for this context   Call SharedPreferences.edit()   Returns a SharedPreferences.Editor instance   Add values with SharedPreferences.Editor   Commit values with SharedPreferences.Editor.commit()   Use SharedPreferences methods, e.g.,   getAll()   getBoolean()   getString() public class SharedPreferenceReadWriteActivity extends Activity { private static String HIGH_SCORE = "high_score"; public void onCreate(Bundle savedInstanceState) { … final SharedPreferences prefs = getPreferences(MODE_PRIVATE); final Button go = … go.setOnClickListener(new OnClickListener() { public void onClick(View v) { … int val= … if (val > prefs.getInt(HIGH_SCORE, 0)) { … SharedPreferences.Editor editor = prefs.edit(); editor.putInt(HIGH_SCORE, val); editor.commit(); } …   Class that supports displaying & modifying user preferences public class DataManagementPreferencesActivity extends Activity { SharedPreferences prefs; final static String USERNAME = "uname"; public void onCreate(Bundle savedInstanceState) { … prefs = PreferenceManager. getDefaultSharedPreferences(getApplicationContext()); final Button button = …; button.setOnClickListener(new OnClickListener() { public void onClick(View v) { startActivity(new Intent (DataManagementPreferencesActivity.this, LoadPreferencesActivity.class)); } }); } … public class LoadPreferencesActivity extends PreferenceActivity { protected void onCreate(Bundle savedInstanceState) { … final SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this); addPreferencesFromResource(R.xml.user_prefs); final EditTextPreference uNamePref = (EditTextPreference) getPreferenceScreen().findPreference(USERNAME); uNamePref.setSummary(prefs.getString(USERNAME, "")); prefs.registerOnSharedPreferenceChangeListener( new OnSharedPreferenceChangeListener() { public void onSharedPreferenceChanged( SharedPreferences sharedPreferences, String key) { uNamePref.setSummary(prefs.getString(USERNAME, "")); } }); … <PreferenceScreen …> <EditTextPreference android:dialogMessage="Enter Your User Name" android:dialogTitle=”Change User Name" android:positiveButtonText="Submit" android:negativeButtonText="Cancel" android:title="User Name" android:key="uname"> </EditTextPreference> </PreferenceScreen>   SQLite provides in ­memory database   Designed to operate within a very small footprint (<300kB) within a single cross ­ platform disk file   Implements most of SQL92   Supports ACID transactions   ACID: atomic, consistent, isolated & durable   Recommended method relies on a helper class called SQLiteOpenHelper   Create a subclass SQLiteOpenHelper   Override onCreate()   Execute CREATE TABLE command   Use Constructor to instantiate subclass   Use SQLiteOpenHelper methods to open & return underlying database public class DatabaseOpenHelper extends SQLiteOpenHelper { final private static String CREATE_CMD = "CREATE TABLE artists (” + “_id”+ “ INTEGER PRIMARY KEY AUTOINCREMENT, ” + “name” + " TEXT NOT NULL)”; public DatabaseOpenHelper(Context context) { super(context, “artist_db”, null, 1); } public void onCreate(SQLiteDatabase db) { db.execSQL(CREATE_CMD); } … public class DatabaseExampleActivity extends ListActivity { final static String columns ={ “_id”, “name”}; static SQLiteDatabase db = null; public void onCreate(Bundle savedInstanceState) { … DatabaseOpenHelper dbHelper = new DatabaseOpenHelper(this); db = dbHelper.getWritableDatabase(); insertArtists(); Cursor c = readArtists(); deleteLadyGaga(); setListAdapter(new SimpleCursorAdapter( this, R.layout.list_layout, c, columns, new int { R.id._id, R.id.name })); } private void insertArtists() { ContentValues values = new ContentValues(); values.put(“name”, "Lady Gaga"); db.insert("artists", null, values); values.clear(); values.put(“name”, "Johnny Cash"); db.insert("artists", null, values); values.clear(); values.put(“name”, "Ludwig von Beethoven"); db.insert("artists", null, values); } private int deleteLadyGaga() { return db.delete( "artists”, “name” +"=?", new String {"Lady Gaga"}); } private Cursor readArtists() { // returns all rows return db.query( "artists", new String {“_id”,”name”}, null, new String {}, null, null, null); } … Cursor c = readArtists(); setListAdapter( new SimpleCursorAdapter( this, R.layout.list_layout, c, new String {“_id”, “name”}, new int { R.id._id, R.id.name })); …   Databases stored in   /data/data/<package name>/databases/   Can examine database with sqlite3   # adb  ­s emulator ­5554 shell   # sqlite3 /data/data/course.examples. DataManagement.DataBaseExample/ databases/artist_db   DataManagementFileInternalMemory   DataManagementFileExternalMemory   DataManagementSharedPreference   DataManagementPreferenceActivity   DataManagementSQL ...
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