Question

请不要投票我的qus。我是在Android的nube。我正在开发一个应用程序，我在其中调用Web服务。结果我想存储在android sql数据库中。它显示一条记录被保存但当我试图检索该记录时它没有显示任何值。我无法弄清楚它出了什么问题。

 public class LyricsStore {
    private static LyricsStore sInstance = null;
    private MusicDB mMusicDatabase = null;

    public LyricsStore(final Context context) {
        mMusicDatabase = MusicDB.getInstance(context);
    }

    public static final synchronized LyricsStore getInstance(final Context context) {
        if (sInstance == null) {
            sInstance = new LyricsStore(context.getApplicationContext());
        }
        return sInstance;
    }


    public void onCreate(final SQLiteDatabase db) {
        db.execSQL("CREATE TABLE IF NOT EXISTS " + LyricsColumns.NAME + " ("
                + LyricsColumns.ID + " LONG NOT NULL,"
                + LyricsColumns.Lyrics + " STRING NOT NULL);");
    }

    public void onUpgrade(final SQLiteDatabase db, final int oldVersion, final int newVersion) {
    }

    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + LyricsColumns.NAME);
        onCreate(db);
    }

    int result = 0;

    public boolean AddUpdateLyrics(long SongID, String SongLyrics) {
        final SQLiteDatabase database = mMusicDatabase.getWritableDatabase();
        database.beginTransaction();
        //onCreate(database);
        Cursor c = getData(database, SongID);
        if (c == null)
            return false;

        if (c.getCount() > 0) {
            ContentValues contentValues = new ContentValues();
            //contentValues.put(LyricsColumns.ID, SongID);
            contentValues.put(LyricsColumns.Lyrics, "this is test");
            result = database.update(LyricsColumns.NAME, contentValues, LyricsColumns.ID + "=?", new String[]{Long.toString(SongID)});
        } else {
            ContentValues contentValues = new ContentValues();
            contentValues.put(LyricsColumns.ID, SongID);
            contentValues.put(LyricsColumns.Lyrics, SongLyrics);
            result = (int) database.insert(LyricsColumns.NAME, null, contentValues);
        }
        database.setTransactionSuccessful();
        database.endTransaction();
        return true;
    }

    public String getLyrics(long songid) {
        String lyrics = "";
        Cursor res = null;
        try {
            SQLiteDatabase db = mMusicDatabase.getReadableDatabase();

            res=  db.query(LyricsColumns.NAME,
                    new String[]{LyricsColumns.ID,LyricsColumns.Lyrics}, null, null, null, null,
                    LyricsColumns.ID + " DESC", "10");

            //res = db.rawQuery("select * from " + LyricsColumns.NAME + " where "+ LyricsColumns.ID + "=" + songid + "", null);
            if (res == null)
                return "";
            if (res.getCount() > 0) {
                lyrics = res.getString(res.getColumnIndex(LyricsColumns.Lyrics));
            }
        } catch (Exception ex) {

        }

        return lyrics;
    }

    public Cursor getData(SQLiteDatabase database, long id) {
        Cursor res = null;
        String error = "";
        try {
            SQLiteDatabase db = mMusicDatabase.getReadableDatabase();
            res = database.rawQuery("select * from " + LyricsColumns.NAME + " where songid=" + id + "", null);
        } catch (Exception ex) {
            error = ex.getMessage();

        }

        return res;
    }

    public interface LyricsColumns {

        String NAME = "lyricsstore";

        String ID = "songid";

        String Lyrics = "lyrics";
    }
}

Answer 1

试试这个，

  public void onUpgrade(final SQLiteDatabase db, final int oldVersion, final int newVersion) {

    db.execSQL("DROP TABLE IF EXISTS " + LyricsColumns.NAME);
    onCreate(db);
 }

Answer 2

您的代码问题：

无需为MusicDB类创建静态实例。

使用onCreate, onUpgrade and default callback类本身中的MusicDb。

从光标读取值时，需要迭代。检查getLyrics类中的代码LyricsStore方法。

改变档案。

MusicDb文件

public class MusicDB extends SQLiteOpenHelper {
    private static final String DB_NAME = "MusicDb";
    private static int mDbVersion = 1;

    public MusicDB(Context context) {
        super(context, DB_NAME, null, mDbVersion);
        Log.v(MusicDB.class.getSimpleName(), "Called music db constructor");
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE IF NOT EXISTS " + DbColumns.MusicDb.NAME + " ("
                + DbColumns.MusicDb.ID + " LONG NOT NULL,"
                + DbColumns.MusicDb.Lyrics + " STRING NOT NULL);");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + DbColumns.MusicDb.NAME);
        onCreate(db);
    }
}

LyricsStore文件

public class LyricsStore {
    private static LyricsStore sInstance = null;
    private MusicDB mMusicDatabase = null;

    private LyricsStore(final Context context) {
        mMusicDatabase = new MusicDB(context);
    }

    public static final synchronized LyricsStore getInstance(final Context context) {
        if (sInstance == null) {
            sInstance = new LyricsStore(context.getApplicationContext());
        }
        return sInstance;
    }

    int result = 0;

    public boolean AddUpdateLyrics(long SongID, String SongLyrics) {
        final SQLiteDatabase database = mMusicDatabase.getWritableDatabase();
        database.beginTransaction();
        Cursor c = getData(database, SongID);
        if (c == null) {
            database.endTransaction();
            return false;
        }

        if (c.getCount() > 0) {
            ContentValues contentValues = new ContentValues();
            contentValues.put(DbColumns.MusicDb.ID, SongID);
            contentValues.put(DbColumns.MusicDb.Lyrics, SongLyrics);
            result = database.update(DbColumns.MusicDb.NAME, contentValues, DbColumns.MusicDb.ID + "=?", new String[]{Long.toString(SongID)});
        } else {
            ContentValues contentValues = new ContentValues();
            contentValues.put(DbColumns.MusicDb.ID, SongID);
            contentValues.put(DbColumns.MusicDb.Lyrics, SongLyrics);
            result = (int) database.insert(DbColumns.MusicDb.NAME, null, contentValues);
        }
        database.setTransactionSuccessful();
        database.endTransaction();
        return true;
    }

    public String getLyrics(long songid) {
        String lyrics = "";
        Cursor res = null;
        try {
            SQLiteDatabase db = mMusicDatabase.getReadableDatabase();

            res=  db.query(DbColumns.MusicDb.NAME,
                    new String[]{DbColumns.MusicDb.ID,DbColumns.MusicDb.Lyrics}, DbColumns.MusicDb.ID + "=?", new String[]{String.valueOf(songid)}, null, null, null);
            if (res == null)
                return "";
            if (res.getCount() > 0) {
                // This is the place you made the mistake. you need to iterate and then try to get the value.
                while (res.moveToNext()) {
                    lyrics = res.getString(res.getColumnIndex(DbColumns.MusicDb.Lyrics));
                }
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }

        return lyrics;
    }

    public Cursor getData(SQLiteDatabase database, long id) {
        Cursor res = null;
        String error = "";
        try {
            res = database.query(DbColumns.MusicDb.NAME, new String[]{DbColumns.MusicDb.ID, DbColumns.MusicDb.Lyrics}, DbColumns.MusicDb.ID + "=?", new String[]{String.valueOf(id)}, null, null, null);
        } catch (Exception ex) {
            error = ex.getMessage();
        }

        return res;
    }
}

DbColumns文件

public class DbColumns {
    public abstract class MusicDb implements BaseColumns {
        public static final String NAME = "lyricsstore";
        public static final String ID = "songid";
        public static final String Lyrics = "lyrics";
    }
}

供参考在github中查看此project。

android数据库更新无法正常工作

2 个答案: