android sqlite数据库有时在sdcard中创建为空

Question

我在我的应用程序中使用sqlite db它几乎每次运行但有时它会给我错误nosuchtablefoundexception，当我从sdcard拉出数据库时它只显示我带有android_metadeta表的空数据库。如果没有复制错误或任何其他异常，它是如何可能的。 我将我的数据库存储在sdcard位置而不是/ data / data文件夹中。 在哪里我可能会弄错，如果有人可以找到。

这是我的dbhelper代码

public static String DB_PATH =Environment.getExternalStorageDirectory()+Constants.DB_PATH;  
public static String DB_NAME = "local_db.sqlite";

public static SQLiteDatabase _database; 

private final Context myContext;
public static String apstorphe = "'";
public static String sep = ","; 

private static final int DB_VERSION_BUILD_1 = 1;
private static final int DB_VERSION_BUILD_2 = 2;

public DatabaseHelper(Context context) 
{    
    super(context, DB_NAME, null, DB_VERSION_BUILD_2);
    this.myContext = context;
    DB_PATH = Environment.getExternalStorageDirectory()+Constants.DB_PATH;
    File fDbDir = new File(DB_PATH);
    if(!fDbDir.exists())
        fDbDir.mkdirs();
}


/**
 * Creates a empty database on the system and rewrites it with your own database.
 * */
public void createDataBase() throws IOException
{
    boolean dbExist = checkDataBase();

    /*SQLiteDatabase db_Read = null;*/

    if(!dbExist)
    {
        //By calling this method and empty database will be created into the default system path
        //of your application so we are gonna be able to overwrite that database with our database.
        /*db_Read = this.getReadableDatabase(); 
        db_Read.close();*/
        try
        {
            copyDataBase();
        } 
        catch (IOException e) 
        {    
            //throw new Error("Error copying database");
            e.printStackTrace();

        }
    } 
}


/**
 * Check if the database already exist to avoid re-copying the file each time you open the application.
 * @return true if it exists, false if it doesn't
 */
private boolean checkDataBase()
{    
    SQLiteDatabase checkDB = null;

    try
    {
        String myPath = DB_PATH + DB_NAME;
        checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE); 
    }
    catch(SQLiteException e)
    {
        //database does't exist yet.     
    }

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

    return checkDB != null ? true : false;
}

/**
 * copy database file from assets to the application directory
 * @throws IOException
 */
private void copyDataBase() throws IOException
{

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

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

    //Open the empty db as the output stream
    OutputStream 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();

}

/**
 * open the connection to database
 * @return
 * @throws SQLException
 */
public SQLiteDatabase openDataBase() throws SQLException
{    
    //Open the database
    if(_database == null)    
    {
    _database = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.OPEN_READWRITE
            | SQLiteDatabase.CREATE_IF_NECESSARY);
    this.getWritableDatabase();
    }
    else if(!_database.isOpen())
    {
        _database = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.OPEN_READWRITE
                | SQLiteDatabase.CREATE_IF_NECESSARY);
    }
    return _database;
}


/**
 * close connection to database
 */
public static void closedatabase() 
{ 
    if(_database != null)
        _database.close(); 
}

@Override
public void onCreate(SQLiteDatabase db) 
{
    Log.e("DB onCreate","db :"+db.getVersion());
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{       
    Log.e("DB Version Upgraded","From old version : "+oldVersion+" to : "+newVersion);

    String upgradeQueryTblOne = "ALTER TABLE "+DbTbls.TBL_ONE+" ADD COLUMN m_type VARCHAR DEFAULT '0'";
    String upgradeQueryTblTwo = "ALTER TABLE "+DbTbls.TBL_TWO+" ADD COLUMN f_type VARCHAR DEFAULT '0'";
    if (oldVersion == DB_VERSION_BUILD_1_34 && newVersion == DB_VERSION_BUILD_1_35)
    {
         if(_database != null)
         {
             _database.execSQL(upgradeQueryTblOne);
             _database.execSQL(upgradeQueryTblTwo);
         }
    }
}





public static boolean deleteDir(File dir) 
{ 
    if (dir.isDirectory()) 
    { 
        String[] children = dir.list(); 
        for (int i=0; i<children.length; i++) 
        { 
            boolean success = deleteDir(new File(dir, children[i])); 
            if (!success) 
            { 
                return false; 
                } 
            } 
        } 
    // The directory is now empty so delete it return dir.delete(); } 
    return dir.delete();
}