从Android内存中读取SQLITE数据库

Question

我已经在Java应用程序上创建了一个sqlite数据库并将它推送到了我的android。我想读这个数据库（也许以后再写入）。目前为止我发现的大多数教程都是在android中创建数据库...

我不认为我需要重写SQLiteOpenHelper类的onCreate（）和onUpdate（）方法吗？另外，在下面的教程中，他创建了表的部分，因为我已经有了我的数据库

任何教程，你可能知道的示例代码？

public class DatabaseHandler extends SQLiteOpenHelper { 

    // All Static variables 
    // Database Version 
    private static final int DATABASE_VERSION = 1; 

    // Database Name 
    private static final String DATABASE_NAME = "contactsManager"; 

    // Contacts table name 
    private static final String TABLE_CONTACTS = "contacts"; 

    // Contacts Table Columns names 
    private static final String KEY_ID = "id"; 
    private static final String KEY_NAME = "name"; 
    private static final String KEY_PH_NO = "phone_number"; 

    public DatabaseHandler(Context context) { 
     super(context, DATABASE_NAME, null, DATABASE_VERSION); 
    } 

    // Creating Tables 
    @Override 
    public void onCreate(SQLiteDatabase db) { 
     String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "(" 
       + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT," 
       + KEY_PH_NO + " TEXT" + ")"; 
     db.execSQL(CREATE_CONTACTS_TABLE); 
    } 

    // Upgrading database 
    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     // Drop older table if existed 
     db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS); 

     // Create tables again 
     onCreate(db); 
    } 

我只需要打开我在内存中的数据库，对我的数据库执行sql查询并获得结果。

Answer 1

您必须先将设备中的数据库复制到设备上的应用程序存储区（或其他可访问位置），然后才能使用它。您不能直接从.apk文件中使用它。

如何去做一个例子：

public class DBAdapter { 

// DB info 
public static final String MAIN_DATABASE_NAME = "yourDB"; 
public static String MAIN_DB_PATH = "/data/data/your.package.name/databases/"; 
public static final int MAIN_DATABASE_VERSION = 1; 

// database control 
private DatabaseHelper mDbHelper; 
private static SQLiteDatabase mDb; 
private static Context mCtx; 

private static class DatabaseHelper extends SQLiteOpenHelper { 
    DatabaseHelper(Context context, String dbname, int dbversion) { 
     super(context, dbname, null, dbversion); 
     if (checkDataBase(dbname)) { 
      openDataBase(dbname); 
     } else { 
      try { 
       this.getReadableDatabase(); 
       copyDataBase(dbname); 
       this.close(); 
       openDataBase(dbname); 
      } catch (IOException e) { 
       throw new Error("Error copying database"); 
      } 
      Toast.makeText(context, 
        "Initial " + dbname + " database has been created", 
        Toast.LENGTH_LONG).show(); 
     } 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) { 
    } 

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

public DBAdapter(Context ctx) { 
    DBAdapter.mCtx = ctx; 
} 

public DBAdapter open(String dbname, int dbversion) throws SQLException { 
    mDbHelper = new DatabaseHelper(mCtx, dbname, dbversion); 
    mDb = mDbHelper.getWritableDatabase(); 
    return this; 
} 

public void close() { 
    mDbHelper.close(); 
} 

private static void copyDataBase(String dbname) throws IOException { 
    InputStream myInput = mCtx.getAssets().open(dbname); 
    String outFileName = MAIN_DB_PATH + dbname; 
    OutputStream myOutput = new FileOutputStream(outFileName); 
    byte[] buffer = new byte[1024]; 
    int length; 
    while ((length = myInput.read(buffer)) > 0) { 
     myOutput.write(buffer, 0, length); 
    } 
    myOutput.flush(); 
    myOutput.close(); 
    myInput.close(); 
} 

private static boolean checkDataBase(String dbname) { 
    SQLiteDatabase checkDB = null; 
    boolean exist = false; 
    try { 
     String db = MAIN_DB_PATH + dbname; 
     checkDB = SQLiteDatabase.openDatabase(db, null, 
       SQLiteDatabase.OPEN_READONLY); 
    } catch (SQLiteException e) { 
     Log.v("db log", "database does't exist"); 
    } 
    if (checkDB != null) { 
     exist = true; 
     checkDB.close(); 
    } 
    return exist; 
} 

private static void openDataBase(String dbname) throws SQLException { 
    String dbPath = MAIN_DB_PATH + dbname; 
    mDb = SQLiteDatabase.openDatabase(dbPath, null, 
      SQLiteDatabase.OPEN_READWRITE); 
} 
}