使用Sqlite数据库时出错

Question

复制数据库文件时出错

错误是

java.io.FileNotFoundException：/data/data/com.clppl.project/database/clppl.sqlite：open failed：ENOENT（没有这样的文件或目录）

这是我的 DatabaseHandler 类

  public class DatabaseHelper extends SQLiteOpenHelper{

    //The Androids default system path of your application database.
    String DB_PATH =null;
    private static String DB_NAME = "clppl.sqlite";
    private SQLiteDatabase myDataBase; 
    private final Context myContext;

    /**
     * Constructor
     * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
     * @param context
     */
    @SuppressLint("SdCardPath")
    public DatabaseHelper(Context context) {

        super(context, DB_NAME, null, 1);
        this.myContext = context;
        DB_PATH="/data/data/com.clppl.project/assets/"; 
    }   

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

        boolean dbExist = checkDataBase();

        if(dbExist){
            //do nothing - database already exist
        }else{

            //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.
            this.getReadableDatabase();

            try {

                copyDataBase();

            } catch (IOException e) {

                throw new Error("Error copying database");

            }
        }

    }

    /**
     * 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_READONLY);

        }catch(SQLiteException e){

            //database does't exist yet.

        }

        if(checkDB != null){

            checkDB.close();

        }

        return checkDB != null ? true : false;
    }

    /**
     * Copies your database from your local assets-folder to the just created empty database in the
     * system folder, from where it can be accessed and handled.
     * This is done by transfering bytestream.
     * */
    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();

    }

    public void openDataBase() throws SQLException{

        //Open the database
        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();

    }



    @Override
    public void onCreate(SQLiteDatabase db) {

    }

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

    }

我打算打开数据库

的Java代码

 myDbHelper= new DatabaseHelper(context);

         try {

          myDbHelper.createDataBase();

        } catch (IOException ioe) {

            throw new Error("Unable to create database");

        }
         try {

            myDbHelper.openDataBase();


            }catch(SQLException sqle){

                throw sqle;

            }

Answer 1

您错误地定义了DB_PATH。您的数据库将驻留在应用程序包目录中不在databases文件夹内的assets文件夹中。不会创建任何assets文件夹。

更改您的路径如下：

      DB_PATH="/data/data/com.clppl.project/databases/";

而不是

       DB_PATH="/data/data/com.clppl.project/assets/";