如何将数据库从资产文件夹复制到数据库文件夹

我的代码如下：

dbhelper.java

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    if (oldVersion >= newVersion) return;
    db.execSQL("DROP DATABASE IF EXISTS " + DATABASE_NAME +";");
    onCreate(db);
}
@Override
public void onCreate(SQLiteDatabase db) {

    //here is the database definition
    db.execSQL("CREATE TABLE dhivehienglish " +
            "(mv TEXT, en TEXT);");
    //insert pre-configured records
    db.execSQL("INSERT INTO dhivehienglish (mv, en) VALUES('ކާރު','car');");
    db.execSQL("INSERT INTO dhivehienglish (mv, en) VALUES('ޖަހާ','hit');");
    db.execSQL("INSERT INTO dhivehienglish (mv, en) VALUES('އިނުން','sit');");
    db.execSQL("INSERT INTO dhivehienglish (mv, en) VALUES('ކެއުން','eat');");
}

}

MainActivity.java

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_carian_kamus);

    //listing data processes
    //-initiate the database connector
    db = dbhelper.getReadableDatabase();

    txtmelayu=(EditText)findViewById(R.id.txtmelayu);
    btncari=(Button)findViewById(R.id.btncari);
    btncari.setOnClickListener(this);
    lblmakna=(TextView)findViewById(R.id.lblmakna);

}//end onCreate

public void onClick(View v){
    //fetch kata melayu dr textbox
    String carimelayu=txtmelayu.getText().toString();
    //kena letak dalam onclick
    //-run SELECT command to fetch data from table
    if (v.getId()==R.id.btncari){
        Cursor cmelayu=db.rawQuery("SELECT * FROM dhivehienglish " +
                "WHERE mv='"+carimelayu+"';", null);
        //-fetch record
        if(cmelayu.getCount()!=0){
            cmelayu.moveToFirst();//go to first row
            String en=cmelayu.getString(1).toString();
            lblmakna.setText(en);
        }
        else{
            //display some notice here saying no data found
            lblmakna.setText("Not found!");}}

}//end onCLick

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_carian_kamus, menu);
    return true;
}

//when menu is selected
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    //call about screen, if user hit "Tentang kami" menu
    if (item.getItemId()==R.id.minsert){
        Intent ins= new Intent (this, InsertActivity.class);
        startActivity(ins);
    }
    return true;
}}

如何从资产文件夹中移动现有数据库并将其用作应用程序沙箱中的本机数据库？非常感谢任何帮助。

修改你的createDataBase()方法在你的DatabaseHandler就像下面的代码：

创建数据库（）：

 public void createDataBase() throws IOException
{
    //If database not exists copy it from the assets

    boolean mDataBaseExist = checkDataBase();
    if(!mDataBaseExist)
    {
        this.getReadableDatabase();
        this.close();
        try 
        {
            //Copy the database from assests
            copyDataBase();
            System.out.println("createDatabase database created");
        } 
        catch (IOException mIOException) 
        {
            throw new Error("ErrorCopyingDataBase");
        }
    }
}

检查数据库（）：

private boolean checkDataBase()
{
    File dbFile = new File(DB_PATH + DB_NAME);
    //Log.v("dbFile", dbFile + "   "+ dbFile.exists());
    return dbFile.exists();
}

复制数据库（）：

//Copy the database from assets
private void copyDataBase() throws IOException
{
    InputStream mInput = mContext.getAssets().open(DB_NAME);
    String outFileName = DB_PATH + DB_NAME;

    OutputStream mOutput = new FileOutputStream(outFileName);
    byte[] mBuffer = new byte[1024];
    int mLength;
    while ((mLength = mInput.read(mBuffer))>0)
    {
        mOutput.write(mBuffer, 0, mLength);
    }
    mOutput.flush();
    mOutput.close();
    mInput.close();
}

Where DB_PATH = /data/data/YOUR_PACKAGE_NAME/Databases/，您可以在 DatabseHandler 的构造中初始化它，如下所示：DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
DB_NAME= YOUR_DATABASE_NAME_THAT_IS_STORED_IN_YOUR_ASSETS_FOLDER

我希望这有帮助。

P.S: DB_NAME 和 DB_PATH 都是字符串。

更新 ：
每当您尝试使用您的实例时DatabaseHelper类，调用这个方法就可以了createDatabase()像这样 ：

DatabaseHandler db = new DatabaseHandler(context);
   try 
    {
        db.createDataBase();
    } 
    catch (IOException io) 
    {
        throw new Error("Unable to create database");
    }

如果数据库尚未复制到数据库目录，它将从资产文件夹复制现有数据库。
我希望这有帮助。