1. CS499 – Mobile Application Development
Fall 2013
Programming the Android Platform
Data Management

2. Data Management Files (internal/external) SQLite database
SharedPreferences (not discussed but a couple of examples included online)

3. File Represents a file system entity identified by a pathname
Classified as internal or external
Internal memory (on the device) usually used for application private files
External memory (removable media) used for public files
Cache files – temporary files
Examples:
DataManagementFileInternalMemory
DataManagementFileExternalMemory

4. File API boolean isDIrectory() String getAbsolutePath()
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

5. Writing an Internal Memory File
// 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();

6. Reading an Internal Memory File
// Open file with ContextWrapper.openFileOutput() FileInputStream fis = openFileOutput(filename); PrintWriter fr = new PrintWriter( new BufferedReader( new InputStreamReader(fis))); // Read from file while (null != (line=fr.readLine())) { // process data } //Close file fr.close();

7. External Memory Files
Removable media may appear/disappear without warning
String Environment.getExternalStorageState()
MEDIA_MOUNTED – present & mounted with read/write access
MEDIA_MOUNTED_READ_ONLY
MEDIA_REMOVED – not present
Need permission to write external files
in AndroidManifest.xml:
<uses-permission android:name= “android.permission.WRITE_EXTERNAL_STORAGE” />

8. Writing an External Memory File
public class FileWriteAndReadActivity extends Activity { public void onCreate(Bundle savedState) { … 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) {} }

9. Writing an External Memory File
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 { is.close(); os.close(); } catch (IOException e) {} …

10. SQLite
SQLite provides in-memory database available to the app that created it
Designed to operate within a very small footprint
Implements most of SQL92
Supports ACID transactions
ACID: atomic, consistent, isolated & durable
Will need to use a content provider to make data available to rest of the system.

11. Databases
This is not a class in databases (CS450) and you aren’t required to know about databases to use SQLite
Data organized in tables where
each row will hold a single element that we are interested in. Each element has a unique identifier called the key
each column is a field of the given elements in the table

12. Example: GradesDB GNumber LastName FirstName Exam1grade Exam2grade
Smith
Bob 80 G
Jones
Davey 70 90 G
White
Betty 85 G
Doe
Jane 20
100 G
John 50 G

13. SQL – Structured Query Language
Standard way to make database requests (creation, queries, insertion, deletion)
Based on relational algebra and tuple relational calculus
Fairly standardized
SELECT LastName, FirstName FROM GradesDB
WHERE Gnumber = G
In Android, requests formulated as method calls with multiple parameters, but has the notation at the core.

14. Opening a Database
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

15. Opening a 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); …

18. Using a Database
public class DatabaseExampleActivity extends ListActivity { final static String[] columns={“_id”, “name”}; static SQLiteDatabase db = null; public void onCreate(Bundle savedState) { … DatabaseOpenHelper dbHelper = new DatabaseOpenHelper(); 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})); }

20. Insertion
private void insertArtists() { ContentValues values = new ContentValues(); values.put(“name”,”Lady Gaga”); db.insert(“artists”,null,values); values.clear(); values.put(“name”,”Johnny Cash”); values.put(“name”,”Ludwig von Beethoven”); }

22. Deletion & Querying
private int deleteLadyGaga() { return db.delete(“artists”,”name =?”, new String[]{“Lady Gaga”}); } private Cursor readArtists() { // SELECT * from artists // i.e. return all rows that match return db.query(“artists”, new String[]{“_id”,”name”}, null, new String[]{},null,null,null);

23. Querying
public Cursor query(String table,
String columns[],
String selection,
String selectionArgs,
String groupBy,
String having,
String orderBy,
String limit)
The parameters are designed to allow queries with the full power of SQL

24. Query Examples
Return all rows where there value matches a given parameter
String[] COLUMNS = new STRING{“FirstName”,”LastName”};
String selection = “Gnumber = ?”;
String[] args = {“G ”};
Cursor result = db.query(“GradesDB”,COLUMNS, selection,
args,null,null,null,null);
Return rows where some field has a particular range
String selection = “Exam1Grade < ? AND Exam2Grade < ?”;
String[] args = {“70”,”70”};

25. Cursor class
 Provides random read-write access to the result set returned by a database query
moveToFirst(), moveToNext(), moveToPosition(int) – iterate through
getString(int index), getInt(int index) – column value associated with a particular row
CursorAdapter lets you put info into a ListView

26. Upgrading

27. Content Providers

31. Examining Databases Databases stored in
/data/data/<package name>/databases
Can examine database with sqlite3