TestDatabase.java (Cont.)
datasource = new CommentsDataSource( this );
datasource.open( );
It calls the SQLiteOpenHelper’s method getWritableDatabase to create and/or open a database that will be used for reading and writing.

List<Comment> values = datasource.getAllComments( );
Retrieve all comments from the database and put them into a list. A List of Comment is written as List<Comment> where List is a generic interface that takes a type parameter—in this case, Comment.

ArrayAdapter<Comment> adapter = new ArrayAdapter(
    this, android.R.layout.simple_list_item_1, values );
setListAdapter( adapter );
To create a visible list there are some specific elements that need to exist in the layout, R.layout.main. One is a ListView node with the attribute: 
     android:id="@android:id/list"
This will be where the list is displayed in the view. A ListView can have its data displayed via an Adapter. An AdapterView (one of its sub-classes is ListView) is a view whose children are determined by an Adapter, which acts as a bridge between an AdapterView and the underlying data for that view. The Adapter provides access to the data items and is also responsible for making a View for each item in the data set. An ArrayAdapter constructor expects three parameters:

  • the current class instance (this),
  • the display layout to use for each list item, and
  • the array of items respectively.

It can be used to populate a list by passing it to setListAdapter( ). Android comes with a few built-in layouts where Android.R.layout.simple_list_item_1 is for a single string.
src/main/java/com/example/wenchen/sqlitedemo/TestDatabase.java 
package com.example.wenchen.sqlitedemo;

import java.util.List;
import java.util.Random;
import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;

public class TestDatabase extends ListActivity {
  private CommentsDataSource datasource;

  @Override
  public void onCreate( Bundle savedInstanceState ) {
    super.onCreate( savedInstanceState );
    setContentView( R.layout.main );

    datasource = new CommentsDataSource( this );
    datasource.open( );

    List<Comment> values = datasource.getAllComments( );

    // Use the SimpleCursorAdapter to show the elements in a ListView.
    ArrayAdapter<Comment> adapter = new ArrayAdapter<Comment>(
      this, android.R.layout.simple_list_item_1, values );
    setListAdapter( adapter );
  }

  // Will be called via the onClick attribute of the buttons in main.xml.
  public void onClick( View view ) {
    @SuppressWarnings( "unchecked" )
    ArrayAdapter<Comment> adapter = ( ArrayAdapter<Comment> ) getListAdapter( );
    Comment comment = null;
    int id = view.getId( );
    if ( id == R.id.add ) {
      String[ ] comments = new String[ ] { "Cool", "Very nice", "Hate it" };
      int nextInt = new Random( ).nextInt( 3 );
      // Save the new comment to the database.
      comment = datasource.createComment( comments[nextInt] );
      adapter.add( comment );
    }
    else if ( id == R.id.delete ) {
      if ( getListAdapter( ).getCount( ) > 0 ) {
        comment = (Comment) getListAdapter( ).getItem( 0 );
        datasource.deleteComment( comment );
        adapter.remove( comment );
      }
    }
    adapter.notifyDataSetChanged( );
  }

  @Override
  protected void onResume( ) {
    datasource.open( );
    super.onResume( );
  }

  @Override
  protected void onPause( ) {
    datasource.close( );
    super.onPause( );
  }
}




      A mother asks her young sons what they want for breakfast.    
      The first little boy says, “I’ll have some @#$%^& pancakes.”    
      The mother angrily sends him to his room for cursing.    
      She glares at the other little boy and asks,    
      “What do you want for breakfast?!”    
      The second boy says, “Well, I sure don’t want the @#$%^& pancakes!”