Question

这是我在DatabaseHelper.class

中的代码

public class DataBaseHelper extends SQLiteOpenHelper {


    private static final int VERSION = 1;
    private static final String DATABASE_NAME = "database_EN_db";
    private static File DATABASE_FILE;

    // This is an indicator if we need to copy the
    // database file.
    private boolean mInvalidDatabaseFile = false;
    private boolean mIsUpgraded = false;
    private Context mContext;

    /**
     * number of users of the database connection.
     * */
    private int mOpenConnections = 0;

    private static DataBaseHelper mInstance;

    synchronized static public DataBaseHelper getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new DataBaseHelper(context.getApplicationContext());
        }
        return mInstance;
    }

    private DataBaseHelper(Context context) {
        super(context, DATABASE_NAME, null, VERSION);
        this.mContext = context;

        SQLiteDatabase db = null;
        try {
            db = getReadableDatabase();
            if (db != null) {
                db.close();
            }

            DATABASE_FILE = context.getDatabasePath(DATABASE_NAME);

            if (mInvalidDatabaseFile) {
                copyDatabase();
            }
            if (mIsUpgraded) {
                doUpgrade();
            }
        } catch (SQLiteException e) {
        } finally {
            if (db != null && db.isOpen()) {
                db.close();
            }
        }
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        mInvalidDatabaseFile = true;
    }

    @Override
    public void onUpgrade(SQLiteDatabase database,
        int old_version, int new_version) {
        mInvalidDatabaseFile = true;
        mIsUpgraded = true;
    }

    /**
     * called if a database upgrade is needed
     */
    private void doUpgrade() {
        // implement the database upgrade here.
    }

    @Override
    public synchronized void onOpen(SQLiteDatabase db) {
        super.onOpen(db);
        // increment the number of users of the database connection.
        mOpenConnections++;
        if (!db.isReadOnly()) {
            // Enable foreign key constraints
            db.execSQL("PRAGMA foreign_keys=ON;");
        }
    }

    /**
     * implementation to avoid closing the database connection while it is in 
     * use by others.
     */
    @Override
    public synchronized void close() {
        mOpenConnections--;
        if (mOpenConnections == 0) {
            super.close();
        }
    }

    private void copyDatabase() {
        AssetManager assetManager = mContext.getResources().getAssets();
        InputStream in = null;
        OutputStream out = null;
        try {
            in = assetManager.open(DATABASE_NAME);
            out = new FileOutputStream(DATABASE_FILE);
            byte[] buffer = new byte[1024];
            int read = 0;
            while ((read = in.read(buffer)) != -1) {
                out.write(buffer, 0, read);
            }
        } catch (IOException e) {
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {}
            }
            if (out != null) {
                try {
                    out.close();
                } catch (IOException e) {}
            }
        }
        setDatabaseVersion();
        mInvalidDatabaseFile = false;
    }

    private void setDatabaseVersion() {
        SQLiteDatabase db = null;
        try {
            db = SQLiteDatabase.openDatabase(DATABASE_FILE.getAbsolutePath(), null,
                SQLiteDatabase.OPEN_READWRITE);
            db.execSQL("PRAGMA user_version = " + VERSION);
        } catch (SQLiteException e ) {
        } finally {
            if (db != null && db.isOpen()) {
                db.close();
            }
        }
    }
}

这是我的数据库DAO：

public class DBDAO {
    protected SQLiteDatabase database;
    private DataBaseHelper dbHelper;
    private Context mContext;

    public DBDAO(Context context) {
        this.mContext = context;
        dbHelper = DataBaseHelper.getInstance(mContext);
        open();

    }

    public DBDAO() {
        // TODO Auto-generated constructor stub
    }

    public void open() throws SQLException {
        if(MainActivity.lang == "English"){
            if(dbHelper == null)
                dbHelper = DataBaseHelper.getInstance(mContext);
            database = dbHelper.getWritableDatabase();
            }   
    }
}

我创建了一个DAO扩展DBDAO并使用此DAO访问数据库：

public class CauHoiDAO extends DBDAO{
public CauHoiDAO(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }
    }

我需要什么..

首次运行时从资产中复制数据库文件。
如果我升级了数据库，我们需要复制新的数据库文件。
我需要让SQLiteOpenHelper无缝地完成它的工作。

但是，结果是错误，因为没有数据库而无法找到表格; 那么，为什么我无法从资源文件夹中预加载我的数据库？有人可以帮我吗??????

无法使用带有SQLiteOpenHelper的预加载sqlite？

0 个答案: