资产文件夹中的数据库文件.它会被更新吗？

Question

我是Android SQLite的新手.这就是我所拥有的:

• 我db.sqlite在我的assets文件夹中.
• db的意图是READ ONLY.用户不会写入它.
• 当应用程序更新时,db.sqlite将替换为新的数据库(我将从项目中删除旧文件并添加新文件).

我关心的是:

• 旧的db文件会被删除吗？(这就是我想要的;用新的替换旧的)
  • 为什么这么问？因为当我调试我的应用程序时,每次更新db文件时,我都需要从设备上卸载应用程序以强制进行更新.当用户从Play商店更新我的应用程序时,用户是否需要这样做？我很害怕.
• 这会受到我实现onCreate(SQLiteDatabase)和onUpgrade(SQLiteDatabase,int,int)的影响吗？
  • 如果是,那么实施它们以满足我的要求的正确方法是什么？

这是我扩展SQLiteOpenHelper类的方法.我按照我在互联网上找到的教程:

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;    
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DataBaseHelper extends SQLiteOpenHelper{

    //The Android's default system path of your application database.
    private static String DB_PATH = "/data/data/com.mydomain.myapp/databases/";
    private static String DB_NAME = "db.sqlite";
    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;
    }   

  /**
     * 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
            Log.i("myapp", "database already exist");
        }else{
            Log.i("myapp", "database NOT exist");

            //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_READWRITE);

    }

    @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) {

    }

  // My public helper methods to access and get content from the database go here

Answer 1

您无法替换数据库,onUpgrade()因为在此方法中数据库已在使用中.你必须在数据库打开之前这样做,就像在你的构造函数中一样DatabaseHelper.由于您无法使用onUpgrade(),您必须自己管理数据库版本控制.使用SharedPreferences是一种很好的方式.检查数据库是否存在(如果已从assets目录复制)并检查数据库是否存在.现在您可以删除旧数据库并从中复制新数据库assets.见下面的实施.

要标记更新的应用程序,assets只需使用新的数据库就可以使用新的数据库DATABASE_VERSION.

private static class DatabaseHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "database.db";
    private static final int DATABASE_VERSION = 1;
    private static final String SP_KEY_DB_VER = "db_ver";
    private final Context mContext;

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        mContext = context;
        initialize();
    }

    /**
     * Initializes database. Creates database if doesn't exist.
     */
    private void initialize() {
        if (databaseExists()) {
            SharedPreferences prefs = PreferenceManager
                    .getDefaultSharedPreferences(mContext);
            int dbVersion = prefs.getInt(SP_KEY_DB_VER, 1);
            if (DATABASE_VERSION != dbVersion) {
                File dbFile = mContext.getDatabasePath(DATABASE_NAME);
                if (!dbFile.delete()) {
                    Log.w(TAG, "Unable to update database");
                }
            }
        }
        if (!databaseExists()) {
            createDatabase();
        }
    }

    /**
     * Returns true if database file exists, false otherwise.
     * @return
     */
    private boolean databaseExists() {
        File dbFile = mContext.getDatabasePath(DATABASE_NAME);
        return dbFile.exists();
    }

    /**
     * Creates database by copying it from assets directory.
     */
    private void createDatabase() {
        String parentPath = mContext.getDatabasePath(DATABASE_NAME).getParent();
        String path = mContext.getDatabasePath(DATABASE_NAME).getPath();

        File file = new File(parentPath);
        if (!file.exists()) {
            if (!file.mkdir()) {
                Log.w(TAG, "Unable to create database directory");
                return;
            }
        }

        InputStream is = null;
        OutputStream os = null;
        try {
            is = mContext.getAssets().open(DATABASE_NAME);
            os = new FileOutputStream(path);

            byte[] buffer = new byte[1024];
            int length;
            while ((length = is.read(buffer)) > 0) {
                os.write(buffer, 0, length);
            }
            os.flush();
            SharedPreferences prefs = PreferenceManager
                    .getDefaultSharedPreferences(mContext);
            SharedPreferences.Editor editor = prefs.edit();
            editor.putInt(SP_KEY_DB_VER, DATABASE_VERSION);
            editor.commit();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (os != null) {
                try {
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
    }

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