Write steps for Linking activities using intents.d) Write the use of onCreate( ), onUpgrade ( ) and getWritable Database( ) methods. With example.e) Write an application to send Email(Using - To, Subject and Message) Intent.f) Explain List View using adapter with the help of example.

d) The onCreate(), onUpgrade() and getWritableDatabase() methods are used in Android SQLite Database.

• onCreate(SQLiteDatabase db): This method is called when the database is created for the first time. This is where the creation of tables and the initial population of the tables should happen. For example:

@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
            + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
            + KEY_PH_NO + " TEXT" + ")";
    db.execSQL(CREATE_CONTACTS_TABLE);
}

• onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion): This method is called when the database needs to be upgraded. It is used to drop tables, add tables, or do anything else it needs to upgrade to the new schema version.

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // Drop older table if existed
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);

    // Create tables again
    onCreate(db);
}

• getWritableDatabase(): Create and/or open a database that will be used for reading and writing.

SQLiteDatabase db = this.getWritableDatabase();

e) To send an email from an Android application, the Intent.ACTION_SEND action is used to launch the email client installed on your Android device.

Intent email = new Intent(Intent.ACTION_SEND);
email.putExtra(Intent.EXTRA_EMAIL, new String[]{ "[email protected]"}); 
email.putExtra(Intent.EXTRA_SUBJECT, "Subject");
email.putExtra(Intent.EXTRA_TEXT, "Message");
email.setType("message/rfc822");
startActivity(Intent.createChooser(email, "Choose an Email client :"));

f) ListView is a view group that displays a list of scrollable items. The list items are automatically inserted to the list using an Adapter that pulls content from a source such as an array or database query and converts each item result into a view that's placed into the list.

public class MainActivity extends Activity {
    ListView listView ;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Get ListView object from xml
        listView = (ListView) findViewById(R.id.list);

        // Defined Array values to show in ListView
        String[] values = new String[] { "Android List View", 
                                         "Adapter implementation",
                                         "Simple List View In Android",
                                         "Create List View Android", 
                                         "Android Example", 
                                         "List View Source Code", 
                                         "List View Array Adapter", 
                                         "Android Example List View" 
                                        };

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
          android.R.layout.simple_list_item_1, android.R.id.text1, values);

        // Assign adapter to ListView
        listView.setAdapter(adapter); 
    }
}