资产文件夹中的数据库文件。 它会被更新吗?

我是Android SQLite的新手。 这就是我所拥有的:

  • 我的assets文件夹中有db.sqlite
  • db的意图是READ ONLY。 用户不会写信给它。
  • 当应用程序更新时, db.sqlite将被替换为新的数据库(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。 用户在从Play商店更新我的应用程序时是否需要执行相同的操作? 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find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 

Solutions Collecting From Web of "资产文件夹中的数据库文件。 它会被更新吗?"

您无法替换onUpgrade()数据库,因为在此方法中数据库已在使用中。 您必须在数据库打开之前执行此操作,例如在DatabaseHelper的构造函数中。 由于无法使用onUpgrade() ,因此必须自行管理数据库版本控制。 使用SharedPreferences是一种很好的方法。 检查数据库是否存在(如果它已从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assets复制新数据库。 见下面的实施。

要标记更新的应用程序,请在assets使用新数据库发布,只需将DATABASE_VERSION标记为常量。

 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) { } } 

经过很多搜索。 我发现这个资产文件夹数据库是只读的。 您无法更新资产文件夹中的数据库。 假设您的下一个应用版本在google play商店中发布,并在assert文件夹中使用新的更新数据库。 如果断言中两个数据库的名称相同(在以前的应用程序和新应用程序中),则android系统将仅读取旧数据库文件。因为文件系统不能包含两个具有相同名称的文件。 您需要做的只是在dataOpenhelper.class中更改新数据库文件名的名称。 像database_1.db。

 public class DatabaseOpenHelper extends SQLiteAssetHelper { private static final String DATABASE_NAME = "dbbasic_5.db"; private static final int DATABASE_VERSION = 3; private Context contaxtDB; // ********* reminder ********** // only change database_name = like dbbasic_5.6.7.8 . // ******* do not change database_version // public DatabaseOpenHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); contaxtDB = context; } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { super.onUpgrade(db, oldVersion, newVersion); } } 

这个工作正常,试试吧

 public class DatabaseHelper extends SQLiteOpenHelper { private static final int DATABASE_VERSION = 3; private static final String SP_KEY_DB_VER = "db_ver"; private static final String DATABASE_NAME = "db.db"; private static String DB_PATH = "/data/data/APP_PACKAGE/databases/"; static SQLiteDatabase db; public Context context; SessionManager session; public DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); this.context = context; session = SessionManager.getInstance(context);; //initialize(); } public void createDataBase() throws IOException { if (!checkDataBase()) { getWritableDatabase(); copyDataBase(); } } public boolean checkDataBase() { /**/ boolean found = new File(DB_PATH + DATABASE_NAME).exists(); if(found) { int dbVersion = Integer.valueOf(session.getData(SP_KEY_DB_VER, "1")); if (DATABASE_VERSION != dbVersion) { File dbFile = context.getDatabasePath(DATABASE_NAME); if (!dbFile.delete()) { Log.w("Warning: ", "Unable to update database"); } found = false; } } return found; } public void copyDataBase() throws IOException { InputStream myInput = this.context.getAssets().open(DATABASE_NAME); OutputStream myOutput = new FileOutputStream(DB_PATH + DATABASE_NAME); 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(); session.saveData(SP_KEY_DB_VER, String.valueOf(DATABASE_VERSION)); //int dbVersion = prefs.in(SP_KEY_DB_VER, 3); } public void openDataBase() throws SQLException { db = SQLiteDatabase.openDatabase(DB_PATH + DATABASE_NAME, null, 0); } } 

MainActivity – > OnCreate

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