从数据库显示数据的问题

Question

数据库：

我试图从数据库中获取数据以在Listview中显示但它不会显示出来。它强制关闭，所以我抬头看着Logcat，它说我的populateFrom()和bindView()是零点异常，但我不认为这是问题所在。然后我尝试调试它们，我注意到它来自query()我认为。因为它与查询有链接，这就是为什么方法无法工作从而显示错误？也许。

我尝试搜索有用的资源，但他们的查询与我的几乎相同。我现在失去了。谁能帮我。？这只是显示数据库中所有data(food)的名称。我检查并没有任何错误拼写。 ;（

TestDatabaseMain.java：

public class TestDatabaseMain extends Activity 
{

    private ListViewHelperTest dbListFoodHelper = null;
    private Cursor OurCursor = null;
    private ListFoodAdapter adapter=null;

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

        ListView myListView = (ListView)findViewById(R.id.listfood);

        //create the database helper
        dbListFoodHelper=new ListViewHelperTest(this);    
        //create the database if user runs the first time
        dbListFoodHelper.createDataBase();

        dbListFoodHelper.openDataBase();

        OurCursor=dbListFoodHelper.getCursor();

        startManagingCursor(OurCursor);

        adapter = new ListFoodAdapter(OurCursor);

        myListView.setAdapter(adapter);

        }
        catch(Exception e)
        {
            Log.e ("ERROR","ERROR IN CODE:  " + e.toString());

            e.printStackTrace();
        }
    }

    class ListFoodAdapter extends CursorAdapter
    {
        ListFoodAdapter(Cursor c) 
        {
            super(TestDatabaseMain.this, c);
        }

        @Override
        public void bindView(View row, Context ctxt, Cursor c) 
        {
            ListFoodHolder holder = (ListFoodHolder)row.getTag();
             holder.populateFrom(c, dbListFoodHelper);
        }

        @Override
        public View newView(Context ctxt, Cursor c, ViewGroup parent) 
        {
            LayoutInflater inflater =getLayoutInflater();
            View row = inflater.inflate(R.layout.row, parent, false);
            ListFoodHolder holder = new ListFoodHolder(row);
            row.setTag(holder);
            return(row);
        }
    }

    static class ListFoodHolder
    {
        private TextView name = null;

        ListFoodHolder(View displayfood)
        {
            name = (TextView)displayfood.findViewById(R.id.listfood);
        }

        public void populateFrom(Cursor c, ListViewHelperTest r) 
        {       
            //to list out the data from the database
            name.setText(r.getName(c));
        }
    }

ListViewHelperTest.java：

public class ListViewHelperTest extends SQLiteOpenHelper
{


    //declare constants of the paths
    private static String DB_PATH = "/data/data/sg.edu.tp.iit.mns/databases/";
    private static String DB_NAME = "ListFoodItem";
    private static int SCHEMA_VERSION=1;

    private static final String TABLE_NAME = "listfooditem"; 
    private static final String FOOD_TITLE = "FoodItem";
    private static final String FOOD_ID = "_id";


    private SQLiteDatabase myDataBase; 
    private final Context myContext;

    public ListViewHelperTest(Context context) 
    {
        super(context, DB_NAME, null, SCHEMA_VERSION);
        this.myContext = context;
        // TODO Auto-generated constructor stub
    }

    @Override
    public void onCreate(SQLiteDatabase db) 
    {
        // TODO Auto-generated method stub
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
    {
        // TODO Auto-generated method stub
    }

    public void createDataBase()
    {
        createDB();
    }

    public void createDB()
    {
        boolean dbExist = DBExists();


        if (!dbExist)
        {
            //overwrite the database with the previous database
            this.getReadableDatabase();

            //copy the overwrite
            copyDBFromRecource();

        }
    }

    private boolean DBExists()
    {

        SQLiteDatabase checkDB = null;

        try
        {
            String myPath = DB_PATH + DB_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null, 
                    SQLiteDatabase.OPEN_READWRITE);
            checkDB.setLocale(Locale.getDefault());
            checkDB.setLockingEnabled(true);
            checkDB.setVersion(1);
        }

        catch(SQLiteException e)
        {
            Log.e("SqlHelper","database not found");
        }


        if(checkDB != null)
        {
            checkDB.close();
        }

        return checkDB != null ? true : false;
    }

    private void copyDBFromRecource()
    {
        InputStream myInput=null;

        // Path to the just created empty db

        try
        {
            //Open your local db as the input stream
            myInput = myContext.getAssets().open(DB_NAME);

            OutputStream myOutput=null;
            // Path to the just created empty db
            String outFileName = DB_PATH + DB_NAME;

            //Open the empty db as the output stream
            myOutput = new FileOutputStream(outFileName);

            //transfer bytes from the inputfile to the outputfile
            byte[] buffer = new byte[1024];
            int length;
            while ((length = myInput.read(buffer))>0)
            {
                myOutput.write(buffer, 0, length);
            }

            //Close the streams
            myOutput.flush();
            myOutput.close();
            myInput.close();
        }
        catch (Exception e)
        {
            throw new Error("Problem coping folders");
        }   

    }
    public void openDataBase() throws SQLException
    {
        String MyPath = DB_PATH + DB_NAME ;
        myDataBase = SQLiteDatabase.openDatabase(MyPath, null, 
                SQLiteDatabase.OPEN_READWRITE);
    }

    @Override
    public synchronized void close()
    {
        if (myDataBase != null)
        {
            myDataBase.close();
        }
        super.close();
    }
    //important!
    public Cursor getCursor()
    {
        SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();

        queryBuilder.setTables(TABLE_NAME);

        String[] ColumnReturn = new String[] {FOOD_ID, FOOD_TITLE};

        //search by string pass(*important*)
        Cursor MYCursor = queryBuilder.query(myDataBase, ColumnReturn, null,
                null, null, null, "FoodItem ASC");      
        return MYCursor;
    }

    public String getName(Cursor c)
    {
        return(c.getString(1));
    }
}

Answer 1

尝试调用Cursor.moveToFirst（）;在做任何事情之前你的光标。