错误当我尝试打开资产文件夹中预先创建的SQLite数据库时

Question

我在 SQLite 中有一个数据库预先创建并插入assets文件夹，遗憾的是我无法访问数据库。

当我尝试使用命令访问数据库时，例如

 DataBaseHelper myDbHelper = new DataBaseHelper(this);
         myDbHelper = new DataBaseHelper(this);

         try {

            myDbHelper.openDataBase();

        }catch(SQLException sqle){

            throw sqle;

        }

我收到此错误：

E/AndroidRuntime(5390): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mysoftware.app/com.mysoftware.app.Home}: android.database.sqlite.SQLiteException: unable to open database file

我的DataBaseHelper类是：

public class DataBaseHelper extends SQLiteOpenHelper{

    private static String DB_PATH = "/data/data/com.mysoftware.app/databases/";

    private static String DB_NAME = "DBTestate";

    private SQLiteDatabase myDataBase; 

    private final Context myContext;


    public DataBaseHelper(Context context) {

        super(context, DB_NAME, null, 1);
        this.myContext = context;
    }   

    public void createDataBase() throws IOException{

        boolean dbExist = checkDataBase();
        SQLiteDatabase db_Read = null;

        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();
            db_Read = this.getReadableDatabase(); 
            db_Read.close();

            try {

                copyDataBase();

            } catch (IOException e) {

                throw new Error("Error copying database");

            }
        }

    }


    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;
    }


    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_READONLY);

    }

    @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) {

    }
    ....

}

我的数据库结构：

Answer 1

只是使用它，这是运行代码，并将生成与资产文件夹

类似的数据库

    private static String LOG_TAG = "DATABASE";
private static String DB_PATH = "/data/data/you_package_name/databases/";
private static String DB_NAME = "Your_DB_Name";
private  static String myPath = DB_PATH + DB_NAME; 
private SQLiteDatabase myDataBase;
private final Context myContext;

public DatabaseHelper(Context context) {
     // TODO Auto-generated constructor stub
    super(context, DB_NAME, null, 1);
    this.myContext=context;
}

public void creatDataBase () throws IOException {
    boolean dbExist = checkDataBase();
    if(dbExist){
        Log.d(LOG_TAG,"DATABASE EXIST");
    }else{
        this.getReadableDatabase();
        copyDataBase();
    }
}

private void copyDataBase() throws IOException {
    // TODO Auto-generated method stub
    InputStream myInput = myContext.getAssets().open(DB_NAME);
    String outFileName = DB_PATH + DB_NAME;
    OutputStream myOutput = new FileOutputStream (outFileName);
    byte[] buffer = new byte[1024];
    int length;
    while((length = myInput.read(buffer))>0)
    myOutput.write(buffer,0,length);
    myOutput.flush();
    myOutput.close();
    myInput.close();
}

private boolean checkDataBase() {
    // TODO Auto-generated method stub
    File dbFile = new File(DB_PATH + DB_NAME);
    return dbFile.exists();
}

public void openDataBase() throws SQLiteException {
    myDataBase = SQLiteDatabase.openDatabase(myPath,null, SQLiteDatabase.NO_LOCALIZED_COLLATORS);
}

@Override
public synchronized void close() {
    // TODO Auto-generated method stub
    if(myDataBase != null)
    myDataBase.close();
    super.close();
}

Answer 2

尝试示例代码here。找到完整的工作示例＆amp;跟着它。

代码探索＆amp;可以找到详细信息here。

Answer 3

验证com.mysoftware.app是否是应用程序的实际名称，文件结构和实际数据库在DDMS文件资源管理器中可见。

此外，对于此示例，您必须将预先构建的数据库放入Eclipse项目的“assets”文件夹中。

Answer 4

我为此而打瞌睡 ：

public class DatabaseHelper extends SQLiteOpenHelper{

    //The Android's default system path of your application database.
    String DB_PATH =null;

    private static String DB_NAME = "extenalDB";

    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
     */
    public DatabaseHelper(Context context) {

        super(context, DB_NAME, null, 1);
        this.myContext = context;
        DB_PATH="/data/data/"+context.getPackageName()+"/"+"databases/";
    }   

  /**
     * 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_READONLY);

    }

    @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) {

    }
 //return cursor
    public Cursor query(String table,String[] columns, String selection,String[] selectionArgs,String groupBy,String having,String[] orderBy,String youare,String myname, Object object, Object object2, Object object3, Object object4){
        return myDataBase.query("EMP_TABLE", null, null, null, null, null, null, null);


    }


}