使用DB帮助程序类使用SQLite数据库中的项填充ExpandableListview

Question

我的数据库中有一个表。这是一个公司目录Android应用程序。我想按类别对公司进行分组。类别是我表格的属性之一。我正在关注这个example。我面临的问题是实现fetchGroup（）方法。 这是因为在该示例中，它们具有用于组的单独表。如果我想按其中一个属性进行分组，如何实现此方法？

这是我的活动课程：

public class CompaniesList extends ListActivity {

    protected SQLiteDatabase db;
    protected Cursor cursor;
    protected ExpandableListAdapter mAdapter;   
    protected ExpandableListView expListView;


    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        expListView = (ExpandableListView) findViewById(R.id.lvExp);
        db = (new DatabaseHelper(this)).getWritableDatabase();
        prepareListData();


        expListView.setOnGroupClickListener(new OnGroupClickListener() {
            // some code, doesn't matter
        });

        expListView.setOnGroupExpandListener(new OnGroupExpandListener() {
            // some code, doesn't matter
        });

        expListView.setOnGroupCollapseListener(new OnGroupCollapseListener() {
           // some code, doesn't matter
        });

        expListView.setOnChildClickListener(new OnChildClickListener() {
           // some code, doesn't matter
        });
    }   

    private void prepareListData() {
       mGroupsCursor = db.fetchGroup();
       getActivity().startManagingCursor(mGroupsCursor);
       mGroupsCursor.moveToFirst();

       ExpandableListView elv = (ExpandableListView)getActivity().findViewById(android.R.id.lvExp);

        mAdapter = new MyExpandableListAdapter(mGroupsCursor, getActivity(),
            R.layout.company_group_item, R.layout.company_list_item,                 
            new String[] { "????" }, new int[] { android.R.id.????? }, 
            new String[] { "name", "address" }, new int[] { R.id.name, R.id.address});              
            lv.setAdapter(mAdapter);              
        }

    }

    class MyAdapter extends SimpleCursorTreeAdapter {

        public MyAdapter(Context context, Cursor cursor, int groupLayout,
            String[] groupFrom, int[] groupTo, int childLayout,
            String[] childFrom, int[] childTo) {
          super(context, cursor, groupLayout, groupFrom, groupTo,
              childLayout, childFrom, childTo);
        }

        protected Cursor getChildrenCursor(Cursor groupCursor) {
         Cursor childCursor =   db.fetchChildren(groupCursor.getString(groupCursor.getColumnIndex("id_category"));            
        getActivity().startManagingCursor(childCursor);
        childCursor.moveToFirst();
        return childCursor;
        }
      }
}   

这是我的db helper类：

public class DatabaseHelper extends SQLiteOpenHelper {

    public static final String DATABASE_NAME = "employee_directory2";
    protected SQLiteDatabase db;

    protected Context context;

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);
        this.context = context;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String s;
        try {
            Toast.makeText(context, "1", 2000).show();
            InputStream in = context.getResources().openRawResource(R.raw.sql);
            DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
            Document doc = builder.parse(in, null);
            NodeList statements = doc.getElementsByTagName("statement");
            for (int i=0; i<statements.getLength(); i++) {
                s = statements.item(i).getChildNodes().item(0).getNodeValue();
                db.execSQL(s);
            }
        } catch (Throwable t) {
            Toast.makeText(context, t.toString(), 50000).show();
        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS employees");
        onCreate(db);
    }

    // THIS IS WRONG. I NEED TO FETCH THE NAME OF CATEGORIES. CATEGORIES - ONE OF THE     // ATTRIBUTES IN MY DB TABLE. 
    public Cursor fetchGroup() {
        String query = "SELECT * FROM employee"; 
        return db.rawQuery(query, null);
    }

    public Cursor fetchChildren(String department) {
        String query = "SELECT * FROM employee WHERE id_department = '" + department + "'";
        return db.rawQuery(query, null);
    }

}