java - Android CursorWindow 仅返回 1 行、1 列

Question

我正在尝试创建一个应用程序来从预先存在的数据库中提取 sqlite 数据，在应用程序运行之前将其复制到目录中。该数据库包含超过 2000 行和大约 20 列。

DBAdapter 类。

package com.t3hh4xx0r.gmusicsniper;

import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DBAdapter {

    public static final String KEY_ROWID = "Id";
    public static final String KEY_TITLE = "Title";
    private static final String DATABASE_NAME = Constants.gMusicSniperDir + Constants.musicDB;
    private static final String DATABASE_TABLE = "MUSIC";

    private static final int DATABASE_VERSION = 37;


    private final Context context; 

    private DatabaseHelper DBHelper;
    private SQLiteDatabase db;

    public DBAdapter(Context ctx) {
        this.context = ctx;
        DBHelper = new DatabaseHelper(context);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper {
        DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase arg0) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
            // TODO Auto-generated method stub

        }
    }

    //---opens the database---
    public DBAdapter open() throws SQLException {
        db = SQLiteDatabase.openDatabase(DATABASE_NAME, null, SQLiteDatabase.OPEN_READONLY);
        return this;
    }

    //---closes the database---    
    public void close() {
        DBHelper.close();
    }

    //---retrieves a particular title---
    public Cursor getTitle(int songFinalValue) throws SQLException {
        Cursor mCursor =
                db.rawQuery("SELECT Title FROM MUSIC WHERE Id = 5899;", null);
                //db.query(DATABASE_TABLE, new String [] {KEY_TITLE}, KEY_ROWID + " = \'" + songFinalValue + "\'", null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

}

“应该”检索数据的方法。在此测试用例中，songFinalValue 为 5899，尽管我已将该值硬编码到查询语句中，以确保问题不在于任何未初始化的变量。

songFinalValue 引用第一列 Id。我尝试返回的值是相应标题的第 13 列。

    private void getTrackName(String songFinal) {
        int songFinalValue = Integer.parseInt(songFinal);
        DBAdapter db = new DBAdapter(this);

        //---get a title---
        db.open();
        Cursor c = db.getTitle(songFinalValue);
        while (c.isAfterLast() == false && c != null) {
           c.getString(13); // will fetch you the data
           c.moveToNext();
            //DisplayTitle(c);
            String cS = String.valueOf(c);               
Log.d("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!", cS);
            }
        db.close();
        }

运行时出现错误

E/CursorWindow(17998): Failed to read row 0, column 13 from a CursorWindow which has 1 rows, 1 columns.
    E/su      (18033): sudb - Database closed
    W/System.err(17998): java.lang.IllegalStateException: Couldn't read row 0, col 13 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.

我已经为此工作了一段时间，并访问了每个指南、教程，并解决了许多 SOF 问题，但我似乎无法弄清楚这个问题。

这是我第一次涉足 SQLite 数据库，也是我的第一个应用程序。我假设这个错误很容易被任何有经验的人解决，它通常最终会成为我的一些愚蠢的错误，尽管我一生都无法弄清楚它会是什么。

Answer 1

在评论中回复。

Take a look at code - db.rawQuery("SELECT Title FROM MUSIC WHERE Id = 5899;", null); This will return single column if given ID matches. – AVD Dec 27 '11 at 4:04