Can'；t从资产文件夹[Android]打开数据库

很抱歉，这个问题很难解决，但我要4个小时才能解决。我正在尝试从/assets文件夹复制数据库，该文件夹可与SQLiteOpenHelper一起使用，但当我尝试打开InputStream时，会出现错误：

 E/Trace: error opening trace file: No such file or directory (2)

代码：

---

你能试试这个代码，然后告诉我结果吗。 确保检查了所有文件名

@Override
protected void onCreate(Bundle savedInstanceState) {   
    //.......

    DatabaseHelper dbHelper = new DatabaseHelper(this);
    dbHelper.createDatabase();

    dbHelper.openDatabase();
    // do stuff
    Cursor data =dbHelper.Sample_use_of_helper();
    dbHelper.close();
}


class DatabaseHelper extends SQLiteOpenHelper {

    private static String DB_PATH = "/data/data/com.mycomp.myapp/databases/";
    private static String DB_NAME = "database.db";
    private SQLiteDatabase myDataBase;
    private final Context myContext;

        public DatabaseHelper (Context context) {
            super(context, DB_NAME, null, 1);
            this.myContext = context;
        }

        public void crateDatabase() throws IOException {
            boolean vtVarMi = isDatabaseExist();

            if (!vtVarMi) {
                this.getReadableDatabase();

                try {
                    copyDataBase();
                } catch (IOException e) {
                    throw new Error("Error copying database");
                }
            }
        }

        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();
        }

        private boolean isDatabaseExist() {
            SQLiteDatabase kontrol = null;

            try {
                String myPath = DB_PATH + DB_NAME;
                kontrol = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

            } catch (SQLiteException e) {
                kontrol = null;
            }

            if (kontrol != null) {
                kontrol.close();
            }
            return kontrol != null ? true : false;
        }

        public void openDataBase() throws SQLException {

            // Open the database
            String myPath = DB_PATH + DB_NAME;
            myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);

        }

        public Cursor Sample_use_of_helper() {

            return myDataBase.query("TABLE_NAME", null, null, null, null, null, null);
        }

        @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) {
        }
    }

---

从db_NAME和.open（“database.db”）中删除.db扩展名
它看起来很难看，但现在同样的东西对我起作用了……
在安装新的apk之前，请清除早期安装的apk的数据

---

如果它仍然不起作用，请说明您的数据库大小。

我真的建议您使用

SQLiteAssetHelper

而不是滚动您自己的代码：您可以发布“copydatabase”功能的其余部分吗？当然可以。我刚刚编辑了我的帖子。您在哪里尝试从Assets文件夹打开文件？看起来更像是试图从外部存储器上的文件夹打开sqlite db。我用sqlite浏览器创建了一个.db文件，然后导入到AndroidStudio中。程序会自动创建带有该文件的资产文件夹，但在运行程序后，会发生错误。我真的不知道怎么了，谢谢！你的代码工作没有任何问题。我不确定我错过了什么，但我会努力找出答案并与大家分享。@AdamK我只是在猜测。也许你的代码只在第一次工作。之后，系统无法覆盖数据库文件。最终解决了这个问题。问题不在于copyDatabase方法，而在于我对DatabaseHelper类角色和getReadableDatabase（）方法的误解。谢谢你的帮助！

@Override
protected void onCreate(Bundle savedInstanceState) {   
    //.......

    DatabaseHelper dbHelper = new DatabaseHelper(this);
    dbHelper.createDatabase();

    dbHelper.openDatabase();
    // do stuff
    Cursor data =dbHelper.Sample_use_of_helper();
    dbHelper.close();
}


class DatabaseHelper extends SQLiteOpenHelper {

    private static String DB_PATH = "/data/data/com.mycomp.myapp/databases/";
    private static String DB_NAME = "database.db";
    private SQLiteDatabase myDataBase;
    private final Context myContext;

        public DatabaseHelper (Context context) {
            super(context, DB_NAME, null, 1);
            this.myContext = context;
        }

        public void crateDatabase() throws IOException {
            boolean vtVarMi = isDatabaseExist();

            if (!vtVarMi) {
                this.getReadableDatabase();

                try {
                    copyDataBase();
                } catch (IOException e) {
                    throw new Error("Error copying database");
                }
            }
        }

        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();
        }

        private boolean isDatabaseExist() {
            SQLiteDatabase kontrol = null;

            try {
                String myPath = DB_PATH + DB_NAME;
                kontrol = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

            } catch (SQLiteException e) {
                kontrol = null;
            }

            if (kontrol != null) {
                kontrol.close();
            }
            return kontrol != null ? true : false;
        }

        public void openDataBase() throws SQLException {

            // Open the database
            String myPath = DB_PATH + DB_NAME;
            myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);

        }

        public Cursor Sample_use_of_helper() {

            return myDataBase.query("TABLE_NAME", null, null, null, null, null, null);
        }

        @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) {
        }
    }