Android Open Source - 2014-Droid-code Database Activity

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License

The source code is released under:

GNU General Public License

Java Source Code

package cs518.sample.dbcursoradapter;
/*from   www . j a  v  a 2s  .  c  o  m*/
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;

/* 
 * DataBaseActivity.class
 * 
 * This is the main Activity , as indicated in the AndroidManifest.xml
 * It is used to populate and display the contents of a simple display
 * It uses a DBHelper class for the sqlite database
 * 
 * Wherever strings constants are used inline "like this" you should use
 * the values directories, the same with any integers, arrays, dimensions or colour constants.
 * 
 * This code uses a ListView with multiple TextViews and a SimpleCursorAdapter 
 * Look at the code SQLite-simple-db to see how to do the same thing
 * but completely programmatically.  
 * This is more efficient and more future proof than implementing it yourself
 * 
 * This code implements an options menu programmatically. 
 * Each menu item click will fire an intent.  
 * 
 * Note this Activity performs queries on the UI thread, this is not a
 * good practice and can lead to ANR, lagging display etc.
 * Soon we will look at ways to avoid long running code on the main UI thread.
 * 
 */
public class DatabaseActivity extends Activity {

  // My DBHelper class
  private static DBHelper dbh;
  public static final int SHOW_AS_ACTION_IF_ROOM = 1;

  private SimpleCursorAdapter sca;
  private Cursor cursor;

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // the projection (fields from the database that we want to use)
    String[] from = { DBHelper.COLUMN_ID, DBHelper.COLUMN_FIRST_NAME,
        DBHelper.COLUMN_LAST_NAME, DBHelper.COLUMN_CLASS,
        DBHelper.COLUMN_GRADE };
    // matching fields on the layout to be used with the adapter
    int[] to = { R.id.tv1, R.id.tv2, R.id.tv3, R.id.tv4, R.id.tv5 };
    setContentView(R.layout.activity_main);
    dbh = DBHelper.getDBHelper(this);
    ListView lv = (ListView) findViewById(R.id.list);
    /*
     * public SimpleCursorAdapter (Context context, int layout, Cursor c,
     * String[] from, int[] to, int flags)
     * 
     * -layout resource identifier of a layout file that defines the views
     * for this list item. The layout file should include at least those
     * named views defined in "to"
     * 
     * -c The database cursor. Can be null if the cursor is not available
     * yet.
     * 
     * -from A list of column names representing the data to bind to the UI.
     * Can be null if the cursor is not available yet.
     * 
     * -to The views that should display column in the "from" parameter.
     * These should all be TextViews. The first N views in this list are
     * given the values of the first N columns in the from parameter. Can be
     * null if the cursor is not available yet.
     * 
     * -flags Flags used to determine the behavior of the adapter, as per
     * CursorAdapter(Context, Cursor, int).
     */
    /*
     * The helper returns a cursor, which is a set of database records.
     */
    cursor = dbh.getGrades();
    sca = new SimpleCursorAdapter(this, R.layout.grade_row, cursor, from,
        to, 0);

    lv.setAdapter(sca);
    lv.setOnItemClickListener(deleteThis);
    // don't close the cursor, it is used by the adapter
    // cursor.close();
  }

  public void onResume() {
    super.onResume();
    logIt("onResume()");
    // we need to get a new cursor and tell the adapter there is new data
    // sca.notifyDataSetChanged(); is not enough if we have added data 
    // to the db it is not in the current cursor
    refreshView();
    /* 
     * NOTE it would be better to not do the refresh here but do it dependent 
     * on the activity result for AddStudent (added or not).  This way the
     * cursor is recreated no matter what happens (data added or not.)
     * I leave it for you to try modifying this code to "fix" this.
     */
  }
  
  public void onPause() {
    super.onPause();
    logIt("onPause()");
    // release resources
    dbh.close();
  }
  public void refreshView() {
    logIt("refreshView()");
    // renew the cursor
    cursor = dbh.getGrades();
    // have the adapter use the new cursor, changeCursor closes old cursor too
    sca.changeCursor(cursor);
    // have the adapter tell the observers
    sca.notifyDataSetChanged();
  }

  /*
   * This is an Item Click Listener, for use with the ListView When an item in
   * the list is clicked, the corresponding database record is deleted.
   */
  public OnItemClickListener deleteThis = new OnItemClickListener() {
    public void onItemClick(AdapterView<?> parent, View view, int position,
        long id) {
      Cursor cursortemp = (Cursor) parent.getItemAtPosition(position);
      for (int i = 0; i < 5; i++)
        logIt(i + "  " + cursortemp.getString(i));
      // CursorAdapter matches id to database record _id
      logIt(" id:" + id);
      // first column is id getInt gets column data as int
      int idDB = cursortemp.getInt(0);
      logIt("_id: " + idDB);
      dbh.deleteStudent((int) id);
      refreshView();
    }
  }; // deleteThis

  @Override
  /*
   * This is an options menu. There are two items programmatically added to
   * the menu: add student fires an intent to invoke AddStudent class show 30%
   * fires an intent to invoke Thirty class
   * 
   * Since we are just firing intents with our menu items there is no need to
   * override onOptionsItemSelected()
   */
  public boolean onCreateOptionsMenu(Menu menu) {
    super.onCreateOptionsMenu(menu);
    // Set up the intents for each button
    Intent add = new Intent(this, AddStudent.class);
    Intent thirty = new Intent(this, Thirty.class);

    // add a menu items with the Intents, should use strings.xml for
    // "Add Student" & "Show 30s"
    /*
     * This could be done through XML but since we are directly firing an
     * intent this is more explicit
     */
    menu.add("Add Student").setIntent(add)
        .setShowAsAction(SHOW_AS_ACTION_IF_ROOM);
    menu.add("Show 30s").setIntent(thirty)
        .setShowAsAction(SHOW_AS_ACTION_IF_ROOM);

    return true;
  }

  // private Context context;
  public void logIt(String msg) {
    final String TAG = "DBCURSOR";
    Log.d(TAG, msg);
  }
}

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