在 Android 中更新预填充的数据库

Question

我在过去 3 个小时内试图这样做。我正在制作一个应用程序，该应用程序将附带一个填充了不会在客户端设备上更改的填充表的数据库。 我设法通过将它放在资产文件夹中并将其作为字节流复制到手机上适当的数据文件夹来做到这一点。问题是当我想更新数据库时，我无法让它工作。我删除了手机数据文件夹中的数据库（从代码中），但复制新数据库总是失败，或者复制的数据库具有适当的大小但其中没有表。 这个怎么做？或者有没有更简单的方法？我可以直接从资产打开数据库吗（如果可以的话，这将是最简单的方法，但我找不到如何从代码访问资产的路径）？

Answer 1

这是我正在使用的代码：

public class DataBaseHelper extends SQLiteOpenHelper {

    private static final String DB_PATH = "/data/data/com.project.mydb/databases/";
    private static final String DB_NAME = "mydb.db";
    private static final String DB_TABLE = "words";
    private static final int DB_VERSION = 6;
    private static final String TAG = "DataBaseHelper";
    int id = 0;
    Random random = new Random();
    private SQLiteDatabase myDataBase;
    private final Context myContext;

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

    @Override
    public void onCreate(SQLiteDatabase db){
        createDB();
    }

    @Override
    public void onUpgrade (SQLiteDatabase db, int oldVersion, int newVersion){
        Log.w(TAG, "Upgrading DB from version " + oldVersion + " to " +
                newVersion + ", which will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS " + DB_TABLE);
        onCreate(db);
    }

    public void createDataBase(){
        createDB();
    }

    private void createDB(){
        boolean dbExist = dbExists();
        if(!dbExist){
            copyDataBase();
        }
        else if(dbExist){
            copyDataBase();
        }
    }

    private boolean dbExists(){
        SQLiteDatabase db = null;
        try{
            String dbPath = DB_PATH + DB_NAME;
            db = SQLiteDatabase.openDatabase(dbPath, null, SQLiteDatabase.OPEN_READWRITE);
            db.setLocale(Locale.getDefault());
            db.setLockingEnabled(true);
            db.setVersion(DB_VERSION);
        }
        catch(SQLiteException e){
            Log.e("SQL Helper", "database not found");
        }
        if(db != null){
            db.close();
        }
        return db != null ? true : false;
    }

    private void copyDataBase(){
        InputStream iStream = null;
        OutputStream oStream = null;
        String outFilePath = DB_PATH + DB_NAME;
        try{
            iStream = myContext.getAssets().open(DB_NAME);
            oStream = new FileOutputStream(outFilePath);
            byte[] buffer = new byte[1024];
            int length;
            while((length = iStream.read(buffer))>0){
                oStream.write(buffer,0,length);
            }
            oStream.flush();
            oStream.close();
            iStream.close();
        }
        catch(IOException ioe){
            throw new Error("Problem copying database from resource file.");
        }
    }

    public void openDataBase() throws SQLException {
        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();
    }
}