DataManagement - Single Application Persistent Data...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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 = { 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 {, })); } 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 {, })); …   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 ...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online