android - sqlite数据库问题android

Question

我在 sqlite 数据库中遇到问题。首先我在外部创建数据库，然后将其放在 Assets 文件夹中。以下代码复制数据库。

public class DbH extends SQLiteOpenHelper{
    private Context mycontext;

    private String DB_PATH = "/data/data/com.android.quotes/databases/";
    private static String ROW_ID="_id";
    private static String DB_NAME = "mdb1.db";
    public SQLiteDatabase myDataBase;
    /*private String DB_PATH = "/data/data/"
        + mycontext.getApplicationContext().getPackageName()
        + "/databases/";
    */

    public DbH(Context context) throws IOException  {
        super(context,DB_NAME,null,1);
        this.mycontext=context;
        boolean dbexist = checkdatabase();
        if(dbexist){
            //System.out.println("Database exists");
            opendatabase(); 
        } else {
            System.out.println("Database doesn't exist");
            createdatabase();
        }
    }

    public void createdatabase() throws IOException{
        boolean dbexist = checkdatabase();
        if(dbexist){
            System.out.println(" Database exists.");
        } else {
            this.getReadableDatabase();
            try{
                copydatabase();
            } catch(IOException e){
            throw new Error("Error copying database");
            }
        }
    }

    private boolean checkdatabase() {
        //SQLiteDatabase checkdb = null;
        boolean checkdb = false;
        try{
            String myPath = DB_PATH + DB_NAME;
            File dbfile = new File(myPath);
            SQLiteDatabase.openDatabase
               (myPath,null,SQLiteDatabase.OPEN_READWRITE);
            checkdb = dbfile.exists();
            } catch(SQLiteException e){
                System.out.println("Database doesn't exist");
            }
            return checkdb;
    }

    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 byte to inputfile to 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
        );
    }

    public synchronized void close(){
        if(myDataBase != null){
            myDataBase.close();
        }
        super.close();
    }

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

    @Override
    public void onCreate(SQLiteDatabase arg0) {
    // TODO Auto-generated method stub
    }

}

在主要 Activity 中，我首先调用 createdatabase，然后调用 opendatabase。现在我在 sqlite 数据库中只创建了两个表，一个是 android_metadata，第二个是 mTab​​le。当我运行程序时，出现以下错误。

1. 虽然数据库已创建并且我可以在 eclipse 中使用文件资源管理器查看它，但只有 android_metadata 表存在而 mTab​​le 不存在。
2. 所以它说从 mTab​​le 中选择 * 时不存在这样的表。

任何我出错的建议。我从一个星期开始拔头发。请帮忙。提前致谢。

Answer 1

首先检查数据库数据库是否存在于内部存储中，如果不存在则复制

private void checkDatabase() {

        StringBuffer dbPath = new StringBuffer();
        File databaseFile;
        // Location of the database file, where it will be stored to access
        // throughout the program.
        dbPath.append("/data/data/");
        dbPath.append(getBaseContext().getPackageName());
        dbPath.append("/databases/");

        // Location of the database file stored in assets folder.
        String storedDatabase = Constants.DATABASE_FILE_NAME;

        // copy the database
        try {

            databaseFile = new File(dbPath.toString(), Constants.DATABASE_FILE_NAME);

            if (databaseFile.exists()) {
                Log.i("database", "database already Exists");

            } else {
                SQLiteDatabase database = openOrCreateDatabase(Constants.DATABASE_FILE_NAME,
                        SQLiteDatabase.OPEN_READONLY, null);
                database.close();
                copyDatasbase(getBaseContext().getAssets(), storedDatabase,
                        dbPath + Constants.DATABASE_FILE_NAME);
            }
        } catch (IOException ioException) {

            ioException.printStackTrace();
        } catch (Exception exception) {

            exception.printStackTrace();
        }

    }

如果数据库不存在则从 Assets 复制到内部存储

private void copyDatasbase(AssetManager manager, String sourceFileName,
            String destinationFileName) throws IOException {

        // Read file from AccessManager
        InputStream inputStream = manager.open(sourceFileName);
        OutputStream outputStream = new FileOutputStream(destinationFileName);
        Log.d("-->", "src: " + sourceFileName);
        Log.d("-->", "Des: " + destinationFileName);
        byte[] buffer = new byte[3072];
        int length;
        while ((length = inputStream.read(buffer)) > 0) {
            // Write the database file to the folder "databases"
            outputStream.write(buffer, 0, length);

        }

        outputStream.flush();
        outputStream.close();
        inputStream.close();

        outputStream = null;
        inputStream = null;
    }